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Biochemistry | Define Biochemistry at Dictionary.com

Historical Examples

Manure spreaders and tree sprayers, reflective of advances in biochemistry, also survived.

"You know what you can do with your physiology and biochemistry," Bowman said succinctly.

From odorless garlic to tofu smelling of pork chops, everything is within the possibility of biochemistry.

biochemistry came into being and, with Liebig as foster-parent, grew into modern Physiology.

But about Bruckian anatomy, physiology or biochemistry, the little emissary would tell them nothing.

Several calves were born, and seemed to be doing well; the biochemistry of Tanith and Khepera were safely alike.

Completing work on his Master's in biochemistry at Cambridge when the Spanish show started.

They actually did have a remarkable grasp of physiology and biochemistry, and constantly sought to learn more.

But, as I've said, with no false modesty, I'm no slouch in my field of biochemistry.

British Dictionary definitions for biochemistry Expand

/bakmstr/

the study of the chemical compounds, reactions, etc, occurring in living organisms

Derived Forms

biochemical, adjectivebiochemically, adverbbiochemist, noun

Word Origin and History for biochemistry Expand

biochemistry in Medicine Expand

biochemistry biochemistry (b'-km'-str) n.

The study of the chemical substances and vital processes occurring in living organisms.

The chemical composition of a particular living system or biological substance.

biochemistry in Science Expand

biochemistry in Culture Expand

The study of the structure and interactions of the complex organic molecules found in living systems.

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Biochemistry | Define Biochemistry at Dictionary.com

Department of Biochemistry | UW-Madison

Congenital sideroblastic anemia due to mutations in the mitochondrial HSP70 homologue HSPA9.

Schmitz-Abe K, Ciesielski SJ, Schmidt PJ, Campagna DR, Rahimov F, Schilke BA, Cuijpers M, Rieneck K, Lausen B, Linenberger ML, Sendamarai AK, Guo C, Hofmann I, Newburger PE, Matthews D, Shimamura A, Snijders PJ, Towne MC, Niemeyer CM, Dziegiel MH,...

Merchant S, Bednarek SY, Birchler JA, Coupland G, Eckardt NA, Genschik P, Greenberg J, Kieber JJ, Kliebenstein DJ, Pogson BJ, Smyth D

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Department of Biochemistry | UW-Madison

Physiology – definition of physiology by The Free Dictionary

physiology - the branch of the biological sciences dealing with the functioning of organisms accommodation - (physiology) the automatic adjustment in focal length of the natural lens of the eye adaptation - (physiology) the responsive adjustment of a sense organ (as the eye) to varying conditions (as of light) abduction - (physiology) moving of a body part away from the central axis of the body adduction - (physiology) moving of a body part toward the central axis of the body control - (physiology) regulation or maintenance of a function or action or reflex etc; "the timing and control of his movements were unimpaired"; "he had lost control of his sphincters" antagonistic muscle - (physiology) a muscle that opposes the action of another; "the biceps and triceps are antagonistic muscles" humour, humor - (Middle Ages) one of the four fluids in the body whose balance was believed to determine your emotional and physical state; "the humors are blood and phlegm and yellow and black bile" neurophysiology - the branch of neuroscience that studies the physiology of the nervous system hemodynamics - the branch of physiology that studies the circulation of the blood and the forces involved kinesiology - the branch of physiology that studies the mechanics and anatomy in relation to human movement myology - the branch of physiology that studies muscles irradiation - (physiology) the spread of sensory neural impulses in the cortex cell death, necrobiosis - (physiology) the normal degeneration and death of living cells (as in various epithelial cells) acid-base balance, acid-base equilibrium - (physiology) the normal equilibrium between acids and alkalis in the body; "with a normal acid-base balance in the body the blood is slightly alkaline" autoregulation - (physiology) processes that maintain a generally constant physiological state in a cell or organism inhibition - (physiology) the process whereby nerves can retard or prevent the functioning of an organ or part; "the inhibition of the heart by the vagus nerve" nutrition - (physiology) the organic process of nourishing or being nourished; the processes by which an organism assimilates food and uses it for growth and maintenance relaxation - (physiology) the gradual lengthening of inactive muscle or muscle fibers stimulation - (physiology) the effect of a stimulus (on nerves or organs etc.) summation - (physiology) the process whereby multiple stimuli can produce a response (in a muscle or nerve or other part) that one stimulus alone does not produce homeostasis - (physiology) metabolic equilibrium actively maintained by several complex biological mechanisms that operate via the autonomic nervous system to offset disrupting changes innervate - stimulate to action; "innervate a muscle or a nerve" irritate - excite to some characteristic action or condition, such as motion, contraction, or nervous impulse, by the application of a stimulus; "irritate the glands of a leaf" abducent, abducting - especially of muscles; drawing away from the midline of the body or from an adjacent part adducent, adducting, adductive - especially of muscles; bringing together or drawing toward the midline of the body or toward an adjacent part afferent - of nerves and nerve impulses; conveying sensory information from the sense organs to the CNS; "afferent nerves"; "afferent impulses" efferent, motorial - of nerves and nerve impulses; conveying information away from the CNS; "efferent nerves and impulses" isometric - of or involving muscular contraction in which tension increases while length remains constant isotonic - of or involving muscular contraction in which tension is constant while length changes voluntary - controlled by individual volition; "voluntary motions"; "voluntary muscles" involuntary - controlled by the autonomic nervous system; without conscious control; "involuntary muscles"; "gave an involuntary start" pressor - increasing (or tending to increase) blood pressure; "pressor reflexes" tonic - of or relating to or producing normal tone or tonus in muscles or tissue; "a tonic reflex"; "tonic muscle contraction" sympathetic - of or relating to the sympathetic nervous system; "sympathetic neurons"; "sympathetic stimulation"

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Physiology - definition of physiology by The Free Dictionary

Human sexuality – Wikipedia, the free encyclopedia

This article is about human sexual anatomy, sexuality and perceptions. For information specifically about sexual activities, see Human sexual activity.

Human sexuality is the capacity of humans to have erotic experiences and responses. A person's sexual orientation can influence their sexual interest and attraction for another person.[1] Sexuality may be experienced and expressed in a variety of ways; including thoughts, fantasies, desires, beliefs, attitudes, values, behaviors, practices, roles, and relationships.[2] These may manifest themselves in biological, physical, emotional, social, or spiritual aspects. The biological and physical aspects of sexuality largely concern the human reproductive functions, including the human sexual response cycle and the basic biological drive that exists in all species.[3] Physical and emotional aspects of sexuality include bonds between individuals that is expressed through profound feelings or physical manifestations of love, trust, and care. Social aspects deal with the effects of human society on one's sexuality, while spirituality concerns an individual's spiritual connection with others. Sexuality also impacts and is impacted upon by cultural, political, legal, philosophical, moral, ethical, and religious aspects of life.

Sexual activity is a vital principle of human living that connects the desires, pleasures, and energy of the body with a knowledge of human intimacy. This results in erotic love, intimate friendship, human mating, and procreation. Interest in sexual activity typically increases when an individual reaches puberty.[4] Opinions differ on the origins of an individual's sexual orientation and sexual behavior. Some argue that sexuality is determined by genetics; some believe it is molded by the environment, and others argue that both of these factors interact to form the individual's sexual orientation.[1] This pertains to the nature versus nurture debate. In the former, one assumes that the features of a person innately correspond to their natural inheritance, exemplified by drives and instincts; the latter refers to the assumption that the features of a person continue to change throughout their development and nurturing, exemplified by ego ideals and formative identifications.

Genetic studies work on the premise that a difference in alleles corresponds to a variation in traits among people.[5] In the study of human chromosomes in human sexuality, research has shown that "ten percent of the population has chromosomal variations that do not fit neatly into the XX-female and XY-male set of categories".[6]

Evolutionary perspectives on human coupling, reproduction and reproduction strategies, and social learning theory provide further views of sexuality.[7] Socio-cultural aspects of sexuality include historical developments and religious beliefs. Examples include Jewish views on sexual pleasure within marriage and some views of other religions on avoidance of sexual pleasures.[3] Some cultures have been described as sexually repressive. The study of sexuality also includes human identity within social groups, sexually transmitted infections (STIs/STDs), and birth control methods.

Certain characteristics are believed to be innate in humans; these characteristics may be modified by the physical and social environment in which people interact.[8] Human sexuality is driven by genetics and mental activity. The sexual drive affects the development of personal identity and social activities.[9][10] An individual's normative, social, cultural, educational, and environmental characteristics moderate the sexual drive.[9] Two well-known theorists have taken opposing positions in the nature-versus-nurture debate. Sigmund Freud believed sexual drives are instinctive. Freud was a firm supporter of the nature argument; he viewed sexuality as the central source of human personality. John Locke believed in the nurture argument. Locke used his theory of the mind as a "tabula rasa" or blank slate: the environment is where one develops one's sexual drives.[11]

Freud's theory assumed that behavior is rooted in biology. He proposed that instincts are the principal motivating forces in the mental realm. He said there are a large number of instincts but they are reduced into two broad groups; Eros (the life instinct), which comprises the self-preserving and erotic instincts, and Thanatos (the death instinct), which comprises instincts invoking aggression, self-destruction, and cruelty.[12] Freud gave sexual drives a centrality in human life, actions, and behaviors that had not been accepted before his proposal. His instinct theory said humans are driven from birth by the desire to acquire and enhance bodily pleasures, thus supporting the nature debate. Freud redefined the term "sexuality" to make it cover any form of pleasure that can be derived from the human body,[12] and said the pre-genital zones are primitive areas of preliminary enjoyment preceding sexual intercourse and orgasm.[13] He also said pleasure lowers tension while displeasure raises it, influencing the sexual drive in humans. His developmentalist perspective was governed by inner forces, especially biological drives and maturation, and his view that humans are biologically inclined to seek sexual gratification demonstrates the nature side of the debate.[11]

Locke (16321704) rejected the assumption that there are innate differences among people and said people are strongly influenced by their social environments, especially by education.[11] He believed it is accurate to view a child's mind as a tabula rasa or blank slate; whatever goes into the mind originates in the surrounding environment.[11] As the person develops, they discover their identities. Locke proposed following a child from its birth and observing the changes that time makes; he said one will find that as the mind, through sensory information, becomes furnished with ideas, it becomes more awake and aware. He said that after some time, the child's mind begins to know the most familiar objects. As the child's brain develops, he or she begins to know the people and social surroundings of daily life, and can then distinguish the known from the unknown. This view supports the nurture side of the debate.[14]

Human sexual behavior is different from that of most other animal species; it seems to be affected by several factors. For example, while most non-human species are driven to partake in sexual behavior when reproduction is possible, humans are not sexually active only to reproduce.[15] The environment, culture, and social setting play major roles in the perception, attitudes, and behaviors of sexuality. Sexual behavior is also affected by the inability to detect sexual stimuli, incorrect labeling, or misattribution. This may in turn impede an individual's sexual performance.[15]

Like other mammals, humans are dioecious, primarily composed of male or female sexes,[16] with a small proportion (around 1%) of intersex individuals, for whom sexual classification may not be as clear.[17] The biological aspects of humans' sexuality deal with the reproductive system, the sexual response cycle, and the factors that affect these aspects. They also deal with the influence of biological factors on other aspects of sexuality, such as organic and neurological responses,[18] heredity, hormonal issues, gender issues, and sexual dysfunction.[19]

Males and females are anatomically similar; this extends to some degree to the development of the reproductive system. As adults, they have different reproductive mechanisms that enable them to perform sexual acts and to reproduce. Men and women react to sexual stimuli in a similar fashion with minor differences. Women have a monthly reproductive cycle, whereas the male sperm production cycle is more continuous.[3]

The hypothalamus is the most important part of the brain for sexual functioning. This is a small area at the base of the brain consisting of several groups of nerve cell bodies that receives input from the limbic system. Studies have shown that within lab animals, destruction of certain areas of the hypothalamus causes the elimination of sexual behavior.[citation needed] The hypothalamus is important because of its relationship to the pituitary gland, which lies beneath it. The pituitary gland secretes hormones that are produced in the hypothalamus and itself. The four important sexual hormones are oxytocin, prolactin, follicle-stimulating hormone, and luteinizing hormone.[3] Oxytocin is also known as the "love hormone"; it is released in both sexes during sexual intercourse when an orgasm is achieved. It is believed that oxytocin is involved with maintaining close relationships.[20][21] The hormone is also released in women when they give birth or are breastfeeding.[22] Both prolactic and oxytocin stimulate milk production in women. Follicle-stimulating hormone (FHS) is responsible for ovulation in women by triggering egg maturity; in men it stimulates sperm production.[23] Luteinizing hormone (LH) triggers ovulation, which is the release of a mature egg.[3]

The mons veneris, also known as the Mound of Venus, is a soft layer of fatty tissue overlaying the pubic bone.[24] Following puberty, this area grows in size. It has many nerve endings and is sensitive to stimulation.[3]

The labia minora and labia majora are collectively known as the lips. The labia majora are two elongated folds of skin extending from the mons to the perineum. Its outer surface becomes covered with hair after puberty. In between the labia majora are the labia minora, two hairless folds of skin that meet above the clitoris to form the clitoral hood, which is highly sensitive to touch. The labia minora become engorged with blood during sexual stimulation, causing them to swell and turn red.[3] The labia minora are composed of connective tissues that are richly supplied with blood vessels which cause the pinkish appearance. Near the anus, the labia minora merge with the labia majora.[25] In a sexually unstimulated state, the labia minora protects the vaginal and urethral opening by covering them.[26] At the base of the labia minora are the Bartholin's glands, which add a few drops of an alkaline fluid to the vagina via ducts; this fluid helps to counteract the acidity of the outer vagina since sperm cannot live in an acidic environment.[3]

The clitoris is developed from the same embryonic tissue as the penis; it or its glans alone consists of as many (or more in some cases) nerve endings as the human penis or glans penis, making it extremely sensitive to touch.[27][28][29] The clitoral glans, which is a small, elongated erectile structure, has only one known functionsexual sensations. It is the main source of orgasm in women.[30][31][32][33] Thick secretions called smegma collect in the clitoris.[3]

The vaginal opening and the urethral opening are only visible when the labia minora are parted. These opening have many nerve endings that make them sensitive to touch. They are surrounded by a ring of sphincter muscles called the bulbocavernosus muscle. Underneath this muscle and on opposite sides of the vaginal opening are the vestibular bulbs, which help the vagina grip the penis by swelling with blood during arousal. Within the vaginal opening is the hymen, a thin membrane that partially covers the opening in many virgins. Rupture of the hymen has been historically considered the loss of one's virginity, though by modern standards, loss of virginity is considered to be the first sexual intercourse. The hymen can be ruptured by activities other than sexual intercourse. The urethral opening connects to the bladder with the urethra; it expels urine from the bladder. This is located below the clitoris and above the vaginal opening.[3]

The breasts are external organs used for sexual pleasure in some cultures. Western culture is one of the few in which they are considered erotic.[3] The breasts are the subcutaneous tissues on the front thorax of the female body.[25] Breasts are modified sweat glands made up of fibrous tissues and fat that provide support and contain nerves, blood vessels and lymphatic vessels.[25] Their purpose is to provide milk to a developing infant. Breasts develop during puberty in response to an increase in estrogen. Each adult breast consists of 15 to 20 milk-producing mammary glands, irregularly shaped lobes that include alveolar glands and a lactiferous duct leading to the nipple. The lobes are separated by dense connective tissues that support the glands and attach them to the tissues on the underlying pectoral muscles.[25] Other connective tissue, which forms dense strands called suspensory ligaments, extends inward from the skin of the breast to the pectoral tissue to support the weight of the breast.[25] Heredity and the quantity of fatty tissue determine the size of the breasts.[3]

The female internal reproductive organs are the vagina, uterus, Fallopian tubes, and ovaries. The vagina is a sheath-like canal that extends from the vulva to the cervix. It receives the penis during intercourse and serves as a depository for sperm. The vagina is also the birth canal; it can expand to 10 centimetres (3.9in) during labor and delivery. The vagina is located between the bladder and the rectum. The vagina is normally collapsed, but during sexual arousal it opens, lengthens, and produces lubrication to allow the insertion of the penis. The vagina has three layered walls; it is a self-cleaning organ with natural bacteria that suppress the production of yeast.[3] The G-spot, named after the Ernst Grfenberg who first reported it in 1950, may be located in the front wall of the vagina and may cause orgasms. This area may vary in size and location between women; in some it may be absent. Various researchers dispute its structure or existence, or regard it as an extension of the clitoris.[34][35][36]

The uterus or womb is a hollow, muscular organ where a fertilized egg (ovum) will implant itself and grow into a fetus.[3] The uterus lies in the pelvic cavity between the bladder and the bowel, and above the vagina. It is usually positioned in a 90-degree angle tilting forward, although in about 20% of women it tilts backwards.[25] The uterus has three layers; the innermost layer is the endometrium, where the egg is implanted. During ovulation, this thickens for implantation. If implantation does not occur, it is sloughed off during menstruation. The cervix is the narrow end of the uterus. The broad part of the uterus is the fundus.[3]

During ovulation, the ovum travels down the Fallopian tubes to the uterus. These extend about four inches (10cm) from both sides of the uterus. Finger-like projections at the ends of the tubes brush the ovaries and receive the ovum once it is released. The ovum then travels for three to four days to the uterus.[3] After sexual intercourse, sperm swim up this funnel from the uterus. The lining of the tube and its secretions sustain the egg and the sperm, encouraging fertilization and nourishing the ovum until it reaches the uterus. If the ovum divides after fertilization, identical twins are produced. If separate eggs are fertilized by different sperm, the mother gives birth to non-identical or fraternal twins.[25]

The ovaries are the female gonads; they develop from the same embryonic tissue as the testicles. The ovaries are suspended by ligaments and are the source where ova are stored and developed before ovulation. The ovaries also produce female hormones progesterone and estrogen. Within the ovaries, each ovum is surrounded by other cells and contained within a capsule called a primary follicle. At puberty, one or more of these follicles are stimulated to mature on a monthly basis. Once matured, these are called Graafian follicles.[3] The female reproductive system does not produce the ova; about 60,000 ova are present at birth, only 400 of which will mature during the woman's lifetime.[25]

Ovulation is based on a monthly cycle; the 14th day is the most fertile. On days one to four, menstruation and production of estrogen and progesterone decreases, and the endometrium starts thinning. The endometrium is sloughed off for the next three to six days. Once menstruation ends, the cycle begins again with an FSH surge from the pituitary gland. Days five to thirteen are known as the pre-ovulatory stage. During this stage, the pituitary gland secretes follicle-stimulating hormone (FSH). A negative feedback loop is enacted when estrogen is secreted to inhibit the release of FSH. Estrogen thickens the endometrium of the uterus. A surge of Luteinizing Hormone (LH) triggers ovulation. On day 14, the LH surge causes a Graafian follicle to surface the ovary. The follicle ruptures and the ripe ovum is expelled into the abdominal cavity. The fallopian tubes pick up the ovum with the fimbria. The cervical mucus changes to aid the movement of sperm. On days 15 to 28the post-ovulatory stage, the Graafian folliclenow called the corpus luteumsecretes estrogen. Production of progesterone increases, inhibiting LH release. The endometrium thickens to prepare for implantation, and the ovum travels down the Fallopian tubes to the uterus. If the ovum is not fertilized and does not implant, menstruation begins.[3]

Males also have both internal and external genitalia that are responsible for procreation and sexual intercourse. Production of spermatozoa (sperm) is also cyclic, but unlike the female ovulation cycle, the sperm production cycle is constantly producing millions of sperm daily.[3]

The male genitalia are the penis and the scrotum. The penis provides a passageway for sperm and urine. An average-sized flaccid penis is about 334 inches (9.5cm) in length and 115 inches (3.0cm) in diameter. When erect, the average penis is between 412 inches (11cm) to 6 inches (15cm) in length and 112 inches (3.8cm) in diameter. The penis's internal structures consist of the shaft, glans, and the root.[3]

The shaft of the penis consists of three cylindrical bodies of spongy tissue filled with blood vessels along its length. Two of these bodies lie side-by-side in the upper portion of the penis called corpora cavernosa. The third, called the corpus spongiosum, is a tube that lies centrally beneath the others and expands at the end to form the tip of the penis (glans).[37]

The raised rim at the border of the shaft and glans is called the corona. The urethra runs through the shaft, providing an exit for sperm and urine. The root consists of the expanded ends of the cavernous bodies, which fan out to form the crura and attach to the pubic bone and the expanded end of the spongy body (bulb). The root is surrounded by two muscles; the bulbocavernosus muscle and the ischiocavernosus muscle, which aid urination and ejaculation. The penis has a foreskin that usually covers the glans; in many cultures, this is removed at birth in a procedure called circumcision.[3] In the scrotum, the testicles are held away from the body, one possible reason for this is so sperm can be produced in an environment slightly lower than normal body temperature.[38][39]

Male internal reproductive structures are the testicles, the duct system, the prostate and seminal vesicles, and the Cowper's gland.[3]

The testicles are the male gonads where sperm and male hormones are produced. Millions of sperm are produced daily in several hundred seminiferous tubules. Cells called the Leydig cells lie between the tubules; these produce hormones called androgens; these consist of testosterone and inhibin. The testicles are held by the spermatic cord, which is a tubelike structure containing blood vessels, nerves, the vas deferens, and a muscle that helps to raise and lower the testicles in response to temperature changes and sexual arousal, in which the testicles are drawn closer to the body.[3]

Sperm are transported through a four-part duct system. The first part of this system is the epididymis. The testicles converge to form the seminiferous tubules, coiled tubes at the top and back of each testicle. The second part of the duct system is the vas deferens, a muscular tube that begins at the lower end of the epididymis.[3] The vas deferens passes upward along the side of the testicles to become part of the spermatic cord.[37] The expanded end is the ampulla, which stores sperm before ejaculation. The third part of the duct system is the ejaculatory ducts, which are 1-inch (2.5cm)-long paired tubes that pass through the prostate gland, where semen is produced.[3] The prostate gland is a solid, chestnut-shaped organ that surrounds the first part of the urethra, which carries urine and semen.[3][37]

The prostate gland and the seminal vesicles produce seminal fluid that is mixed with sperm to create semen.[3] The prostate gland lies under the bladder and in front of the rectum. It consists of two main zones: the inner zone that produces secretions to keep the lining of the male urethra moist and the outer zone that produces seminal fluids to facilitate the passage of semen.[37] The seminal vesicles secrete fructose for sperm activation and mobilization, prostaglandins to cause uterine contractions that aid movement through the uterus, and bases that help neutralize the acidity of the vagina. The Cowper's glands, or bulbourethral glands, are two pea sized structures beneath the prostate.

The sexual response cycle is a model that describes the physiological responses that occur during sexual activity. This model was created by William Masters and Virginia Johnson. According to Masters and Johnson, the human sexual response cycle consists of four phases; excitement, plateau, orgasm, and resolution. During the excitement phase, one attains the intrinsic motivation to have sex. The plateau phase is the precursor to orgasm, which may be mostly biological for men and mostly psychological for women. Orgasm is the release of tension, and the resolution period is the unaroused state before the cycle begins again.[3]

The male sexual response cycle starts in the excitement phase; two centers in the spine are responsible for erections. Vasoconstriction in the penis begins, the heart rate increases, the scrotum thickens, the spermatic cord shortens, and the testicles become engorged with blood. In the plateau phase, the penis increases in diameter, the testicles become more engorged, and the Cowper's glands secrete pre-seminal fluid. The orgasm phase, during which rhythmic contractions occur every 0.8 seconds[verification needed], consists of two phases; the emission phase, in which contractions of the vas deferens, prostate, and seminal vesicles encourage ejaculation, which is the second phase of orgasm. Ejaculation is called the expulsion phase; it cannot be reached without an orgasm. In the resolution phase, the male is now in an unaroused state consisting of a refactory (rest) period before the cycle can begin. This rest period may increase with age.[3]

The female sexual response begins with the excitement phase, which can last from several minutes to several hours. Characteristics of this phase include increased heart and respiratory rate, and an elevation of blood pressure. Flushed skin or blotches of redness may occur on the chest and back; breasts increase slightly in size and nipples may become hardened and erect. The onset of vasocongestion results in swelling of the clitoris, labia minora, and vagina. The muscle that surrounds the vaginal opening tightens and the uterus elevates and grows in size. The vaginal walls begin to produce a lubricating liquid. The second phase, called the plateau phase, is characterized primarily by the intensification of the changes begun during the excitement phase. The plateau phase extends to the brink of orgasm, which initiates the resolution stage; the reversal of the changes begun during the excitement phase. During the orgasm stage the heart rate, blood pressure, muscle tension, and breathing rates peak. The pelvic muscle near the vagina, the anal sphincter, and the uterus contract. Muscle contractions in the vaginal area create a high level of pleasure, though all orgasms are centered in the clitoris.[3][40][41][42]

Sexual disorders, according to the DSM-IV-TR, are disturbances in sexual desire and psycho-physiological changes that characterize the sexual response cycle and cause marked distress, and interpersonal difficulty. There are four major categories of sexual problems: desire disorders, arousal disorders, orgasmic disorders, and sexual pain disorders.[3]

Sexuality in humans generates profound emotional and psychological responses. Some theorists identify sexuality as the central source of human personality.[43] Psychological studies of sexuality focus on psychological influences that affect sexual behavior and experiences.[19] Early psychological analyses were carried out by Sigmund Freud, who believed in a psychoanalytic approach. He also proposed the concepts of psychosexual development and the Oedipus complex, among other theories.[44]

Gender identity is a person's sense of self-identification as female, male, both, neither, or somewhere in between. The social construction of gender has been discussed by many scholars, including Judith Butler. More recent research has focused upon the influence of feminist theory and courtship.[45][46]

Sexual behavior and intimate relationships are strongly influenced by a person's sexual orientation.[47] Sexual orientation refers to the degree of emotional and physical attraction to members of the opposite sex, same sex, or both sexes.[47] Heterosexual people are attracted to the members of the opposite sex. Homosexual people are attracted to people of the same sex. Those who are bisexual are attracted to both men and women.

Before the High Middle Ages, homosexual acts appear to have been ignored or tolerated by the Christian church.[48] During the 12th century, hostility toward homosexuality began to spread throughout religious and secular institutions. By the end of the 19th century, it was viewed as a pathology.[48]Havelock Ellis and Sigmund Freud adopted more accepting stances; Ellis said homosexuality was inborn and therefore not immoral, not a disease, and that many homosexuals made significant contributions to society.[48] Freud wrote that all human beings as capable of becoming either heterosexual or homosexual; neither orientation was assumed to be innate.[49] According to Freud, a person's orientation depended on the resolution of the Oedipus complex. He said male homosexuality resulted when a young boy had an authoritarian, rejecting mother and turned to his father for love and affection, and later to men in general. He said female homosexuality developed when a girl loved her mother and identified with her father, and became fixated at that stage.[49]

Freud and Ellis said homosexuality resulted from reversed gender roles. In the early 21st century, this view is reinforced by the media's portrayal of male homosexuals as effeminate and female homosexuals as masculine.[49] A person's conformity or non-conformity to gender stereotypes does not always predict sexual orientation. Society believes that if a man is masculine he is heterosexual, and if a man is feminine he is homosexual. There is no strong evidence that a homosexual or bisexual orientation must be associated with atypical gender roles. By the early 21st century, homosexuality was no longer considered to be a pathology. Many factors, including: genetic factors, anatomical factors, birth order, and hormones in the prenatal environment, have been linked to homosexuality.[49]

Other than the need to procreate, there are many other reasons people have sex. According to one study conducted on college students (Meston & Buss, 2007), the four main reasons for sexual activities are; physical attraction, as a means to an end, to increase emotional connection, and to alleviate insecurity.[50]

In the past[when?], children were often assumed not to have sexuality until later development. Sigmund Freud was one of the first researchers to take child sexuality seriously. His ideas, such as psychosexual development and the Oedipus conflict, have been much debated but acknowledging the existence of child sexuality was an important development.[51] Freud gave sexual drives an importance and centrality in human life, actions, and behavior; he said sexual drives exist and can be discerned in children from birth. He explains this in his theory of infantile sexuality, and says sexual energy (libido) is the most important motivating force in adult life. Freud wrote about the importance of interpersonal relationships to one's sexual and emotional development. From birth, the mother's connection to the infant affects the infant's later capacity for pleasure and attachment.[52] Freud described two currents of emotional life; an affectionate current, including our bonds with the important people in our lives; and a sensual current, including our wish to gratify sexual impulses. During adolescence, a young person tries to integrate these two emotional currents.[53]

Alfred Kinsey also examined child sexuality in his Kinsey Reports. Children are naturally curious about their bodies and sexual functions. For example, they wonder where babies come from, they notice the differences between males and females, and many engage in genital play, which is often mistaken for masturbation. Child sex play, also known as playing doctor, includes exhibiting or inspecting the genitals. Many children take part in some sex play, typically with siblings or friends.[51] Sex play with others usually decreases as children grow, but they may later possess romantic interest in their peers. Curiosity levels remain high during these years, but the main surge in sexual interest occurs in adolescence.[51]

Adult sexuality originates in childhood. However, like many other human capacities, sexuality is not fixed, but matures and develops. A common stereotype suggests that people tend to lose interest in and ability to engage in sexual acts once they reach late adulthood. This stereotype is reinforced by Western pop culture, which often ridicules older adults who try to engage in sexual activities. Men are shown suffering heart attacks from over-excitement, and women are depicted as grateful if anyone shows an interest in them. The term "dirty old man" is applied to older men who show an interest in sex beyond a level the speaker considered appropriate . The language for older women, by contrast, is sexless, and older women are portrayed as sexually unattractive and undesirable. Sexuality, however, is similar to most other aspects of aging. Age does not necessarily change the need or desire to be sexually expressive or active. If a couple has been in a long-term relationship, the frequency of sexual activity may decrease, but not necessarily their satisfaction with each other. Many couples find that the type of sexual expression may change, and that with age and the term of relationship there is increased intimacy and love. If sex and sexual intimacy are important aspects in one's life during young and middle adulthood, they will continue to be factors in older adulthood.

Human sexuality can be understood as part of the social life of humans, which is governed by implied rules of behavior and the status quo. This narrows the view to groups within a society.[19] The socio-cultural context of society, including the effects of politics and the mass media, influences and forms social norms. Before the early 21st century, people fought for their civil rights. The civil rights movements helped to bring about massive changes in social norms; examples include the sexual revolution and the rise of feminism.[54][55]

The link between constructed sexual meanings and racial ideologies has been studied. Sexual meanings are constructed to maintain racial-ethnic-national boundaries by denigration of "others" and regulation of sexual behavior within the group. According to Joane Nagel, "Both adherence to and deviation from such approved behaviors, define and reinforce racial, ethnic, and nationalist regimes".[56][57]

The age and manner in which children are informed of issues of sexuality is a matter of sex education. The school systems in almost all developed countries have some form of sex education, but the nature of the issues covered varies widely. In some countries, such as Australia and much of Europe, age-appropriate sex education often begins in pre-school, whereas other countries leave sex education to the pre-teenage and teenage years.[58] Sex education covers a range of topics, including the physical, mental, and social aspects of sexual behavior. Geographic location also plays a role in society's opinion of the appropriate age for children to learn about sexuality. According to TIME magazine and CNN, 74% of teenagers in the United States reported that their major sources of sexual information were their peers and the media, compared to 10% who named their parents or a sex education course.[3]

In some religions, sexual behavior is regarded as primarily spiritual. In others it is treated as primarily physical. Some hold that sexual behavior is only spiritual within certain kinds of relationships, when used for specific purposes, or when incorporated into religious ritual. In some religions there are no distinctions between the physical and the spiritual, whereas some religions view human sexuality as a way of completing the gap that exists between the spiritual and the physical.[59]

Many religious conservatives, especially those of Abrahamic religions and Christianity in particular, tend to view sexuality in terms of behavior (i.e. homosexuality or heterosexuality is what someone does) and certain sexualities such as bisexuality tend to be ignored as a result of this. These conservatives tend to promote celibacy for gay people and may also tend to believe that sexuality can be changed through conversion therapy[60] or prayer to become an ex-gay. They may also see homosexuality as a form of mental illness, something that ought to be criminalised, an immoral abomination, caused by ineffective parenting, and view same-sex marriage as a threat to society.[61]

On the other hand, most religious liberals define sexuality-related labels in terms of sexual attraction and self-identification.[60] They may also view same-sex activity as morally neutral and legally acceptable as opposite-sex activity, unrelated to mental illness, genetically or environmentally caused (but not as the result of bad parenting), and fixed. They also tend to be more in favor of same-sex marriage.[61]

According to Judaism, sex between man and woman within marriage is sacred and should be enjoyed; celibacy is considered sinful.[3]

The Roman Catholic Church teaches that sexuality is "noble and worthy"[62] but that it must be used in accordance with natural law. For this reason, all sexual activity must occur in the context of a marriage between a man and a woman, and must not be divorced from the possibility of conception. All forms of sex without the possibility of conception are considered intrinsically disordered and sinful, such as the use of contraceptives, masturbation, and homosexual acts.[63]

In Islam, sexual desire is considered to be a natural urge that should not be suppressed, although the concept of free sex is not accepted; these urges should be fulfilled responsibly. Marriage is considered to be a good deed; it does not hinder spiritual wayfaring. The term used for marriage within the Quran is nikah, which literally means sexual intercourse. Although Islamic sexuality is restrained via Islamic sexual jurisprudence, it emphasizes sexual pleasure within marriage. It is acceptable for a man to have more than one wife, but he must take care of those wives physically, mentally, emotionally, financially, and spiritually.[64] Muslims believe that sexual intercourse is an act of worship that fulfils emotional and physical needs, and that producing children is one way in which humans can contribute to God's creation, and Islam discourages celibacy once an individual is married. However, homosexuality is strictly forbidden in Islam, and some Muslim lawyers have suggested that gay people should be put to death.[65]

Hinduism emphasizes that sex is only appropriate between husband and wife, in which satisfying sexual urges through sexual pleasure is an important duty of marriage. Any sex before marriage is considered to interfere with intellectual development, especially between birth and the age of 25, which is said to be brahmacharya and this should be avoided. Kama (sensual pleasures) is one of the four purusharthas or aims of life (dharma, artha, kama, and moksha).[66] The Hindu Kama Sutra deals partially with sexual intercourse; it is not exclusively a sexual or religious work.[67][68][69]

Sikhism views chastity as important, as Sikhs believe that the divine spark of Waheguru is present inside every individual's body, therefore it is important for one to keep clean and pure. Sexual activity is limited to married couples, and extramarital sex is forbidden. Marriage is seen as a commitment to Waheguru and should be viewed as part of spiritual companionship, rather than just sexual intercourse, and monogamy is deeply emphasised in Sikhism. Any other way of living is discouraged, including celibacy and homosexuality. However, in comparison to other religions, the issue of sexuality in Sikhism is not considered one of paramount importance.[70]

Sexuality has been an important vital part of human existence throughout history.[72] All civilizations have managed sexuality through sexual standards, representations, and behavior.[72]

Before the rise of agriculture, groups of hunter/gatherers (H/G) and nomads inhabited the world. Within these groups, some implications of male dominance existed, but there were signs that women were active participants in sexuality, with bargaining power of their own. These hunter/gatherers had less restrictive sexual standards that emphasized sexual pleasure and enjoyment, but with definite rules and constraints. Some underlying continuities or key regulatory standards contended with the tension between recognition of pleasure, interest, and the need to procreate for the sake of social order and economic survival. H/G groups also placed high value on certain types of sexual symbolism. Two common tensions in H/G societies are expressed in their art, which emphasizes male sexuality and prowess, with equally common tendencies to blur gender lines in sexual matters. One example of these male-dominated portrayals is the Egyptian creation myth, in which the sun god Atum masturbates in the water, creating the Nile River. In Sumerian myth, the Gods' semen filled the Tigris.[72]

Once agricultural societies emerged, the sexual framework shifted in ways that persisted for many millennia in much of Asia, Africa, Europe, and parts of the Americas. One common characteristic new to these societies was the collective supervision of sexual behavior due to urbanization, and the growth of population and population density. Children would commonly witness parents having sex because many families shared the same sleeping quarters. Due to landownership, determination of children's paternity became important, and society and family life became patriarchal. These changes in sexual ideology were used to control female sexuality and to differentiate standards by gender. With these ideologies, sexual possessiveness and increases in jealousy emerged. With the domestication of animals, new opportunities for bestiality arose. Males mostly performed these types of sexual acts and many societies acquired firm rules against it. These acts also explain the many depictions of half-human, half-animal mythical creatures, and the sports of gods and goddesses with animals.[72] While retaining the precedents of earlier civilizations, each classical civilization established a somewhat distinctive approach to gender, artistic expression of sexual beauty, and to behaviors such as homosexuality. Some of these distinctions are portrayed in sex manuals, which were also common among civilizations in China, Greece, Rome, Persia, and India; each has its own sexual history.[72]

During the beginning of the industrial revolution of the 18th and 19th centuries, many changes in sexual standards occurred. New, dramatic, artificial birth control devices such as the condom and diaphragm were introduced. Doctors started claiming a new role in sexual matters, urging that their advice was crucial to sexual morality and health. New pornographic industries grew and Japan adopted its first laws against homosexuality. In western societies, the definition of homosexuality was constantly changing; western influence on other cultures became more prevalent. New contacts created serious issues around sexuality and sexual traditions. There were also major shifts in sexual behavior. During this period, puberty began occurring at younger ages, so a new focus on adolescence as a time of sexual confusion and danger emerged. There was a new focus on the purpose of marriage; it was increasing regarded as being for love rather than only for economics and reproduction.[72]

Alfred Kinsey initiated the modern era of sex research. He collected data from questionnaires given to his students at Indiana University, but then switched to personal interviews about sexual behaviors. Kinsey and his colleagues sampled 5,300 men and 5,940 women. He found that most people masturbated, that many engaged in oral sex, that women are capable of having multiple orgasms, and that many men had had some type of homosexual experience in their lifetimes. Many[who?] believe he was the major influence in changing 20th century attitudes about sex. Kinsey Institute for Research in Sex, Gender, and Reproduction at Indiana University continues to be a major center for the study of human sexuality.[3] Before William Masters, a physician, and Virginia Johnson, a behavioral scientist, the study of anatomy and physiological studies of sex was still limited to experiments with laboratory animals. Masters and Johnson started to directly observe and record the physical responses in humans that are engaged in sexual activity under laboratory settings. They observed 10,000 episodes of sexual acts between 312 men and 382 women. This led to methods of treating clinical problems and abnormalities. Masters and Johnson opened the first sex therapy clinic in 1965. In 1970, they described their therapeutic techniques in their book, Human Sexual Inadequacy.[3]

Reproductive and sexual rights encompass the concept of applying human rights to issues related to reproduction and sexuality.[73] This concept is a modern one, and remains controversial, especially outside the West, since it deals, directly and indirectly, with issues such as contraception, LGBT rights, abortion, sex education, freedom to choose a partner, freedom to decide whether to be sexually active or not, right to bodily integrity, freedom to decide whether or not, and when, to have children.[74][75][76] According to the Swedish government, "sexual rights include the right of all people to decide over their own bodies and sexuality" and "reproductive rights comprise the right of individuals to decide on the number of children they have and the intervals at which they are born."[77] Such rights are not accepted in all cultures, with practices such criminalization of consensual sexual activities (such as those related to homosexual acts and sexual acts outside marriage), acceptance of forced marriage and child marriage, failure to criminalize all non-consensual sexual encounters (such as marital rape), female genital mutilation, or restricted availability of contraception, being common around the world.[78][79]

In humans, sexual intercourse and sexual activity in general have been shown to have health benefits, such as an improved sense of smell,[80]stress and blood pressure reduction,[81][82] increased immunity,[83] and decreased risk of prostate cancer.[84][85][86] Sexual intimacy and orgasms increase levels of oxytocin, which helps people bond and build trust.[87][88][89] A long-term study of 3,500 people between ages 30 and 101 by clinical neuropsychologist David Weeks, MD, head of old-age psychology at the Royal Edinburgh Hospital in Scotland, said he found that "sex helps you look between four and seven years younger", according to impartial ratings of the subjects' photographs. Exclusive causation, however, is unclear, and the benefits may be indirectly related to sex and directly related to significant reductions in stress, greater contentment, and better sleep that sex promotes.[90][91][92]

Sexual intercourse can also be a disease vector.[93] There are 19 million new cases of sexually transmitted diseases (STD) every year in the U.S.,[94] and worldwide there are over 340 million STD infections each year.[95] More than half of these occur in adolescents and young adults aged 1524 years.[96] At least one in four U.S. teenage girls has a sexually transmitted disease.[94][97] In the U.S., about 30% of 1517-year olds have had sexual intercourse, but only about 80% of 1519-year olds report using condoms for their first sexual intercourse.[98] In one study, more than 75% of young women age 1825 years felt they were at low risk of acquiring an STD.[99]

People both consciously and subconsciously seek to attract others with whom they can form deep relationships. This may be for companionship, procreation, or an intimate relationship. This involves interactive processes whereby people find and attract potential partners and maintain a relationship. These processes, which involve attracting one or more partners and maintaining sexual interest, can include:

The law regulates human sexuality in several ways, including: the criminal status of certain sexual behaviors; granting individuals the privacy or autonomy of individuals to make their own sexual decisions; protections regarding equality and non-discrimination; the recognition and protection of certain individuals' rights; legislation regarding marriage and the family; the status of laws protecting individuals from violence, harassment and persecution.[102]

Issues regarding human sexuality and human sexual orientation became entrenched in law in the Western world by the latter half of the twentieth century, as part of the gay liberation movement encouraging LGBT individuals to "come out of the closet" and engaging with the legal system, primarily through courts. Therefore, many issues regarding human sexuality and the law are found in the opinions of the courts.[103]

While the issue of privacy has been useful to sexual rights claims, some scholars have criticized its usefulness, saying that this perspective is too narrow and restrictive. The law is often slow to intervene in certain forms of coercive behavior that can limit individuals' control over their own sexuality (such as female genital mutilation, forced marriages or lack of access to reproductive health care). Many of these injustices are often perpetuated wholly or in part by private individuals rather than state agents, and as a result, there is an ongoing debate about the extent of state responsibility to prevent harmful practices and to investigate such practices when they do occur.[102]

State intervention with regards to sexuality also occurs, and is considered acceptable by some, in certain instances (e.g. same-sex sexual activity or prostitution).[102]

Niall Richardson, Clarissa Smith and Angela Werndly (2013) Studying Sexualities: Theories, Representations, Cultures (London: Palgrave MacMillan)

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Behavior – Wikipedia, the free encyclopedia

Behavior or behaviour (see spelling differences) is the range of actions and mannerisms made by individuals, organisms, systems, or artificial entities in conjunction with themselves or their environment, which includes the other systems or organisms around as well as the (inanimate) physical environment. It is the response of the system or organism to various stimuli or inputs, whether internal or external, conscious or subconscious, overt or covert, and voluntary or involuntary.[1]

Although there is some disagreement as to how to precisely define behavior in a biological context, one common interpretation based on a meta-analysis of scientific literature states that "behavior is the internally coordinated responses (actions or inactions) of whole living organisms (individuals or groups) to internal and/or external stimuli"[2]

A broader definition of behavior, applicable to plants and other organisms, is similar to the concept of phenotypic plasticity. It describes behavior as a response to an event or environment change during the course of the lifetime of an individual, differing from other physiological or biochemical changes that occurs much rapidly, and excluding changes that are result of development (ontogeny).[3][4]

Behaviors can be either innate or learned.

Behavior can be regarded as any action of an organism that changes its relationship to its environment. Behavior provides outputs from the organism to the environment.[5]

Human behavior is believed to be influenced by the endocrine system and the nervous system. It is most commonly believed that complexity in the behavior of an organism is correlated to the complexity of its nervous system. Generally, organisms with more complex nervous systems have a greater capacity to learn new responses and thus adjust their behavior.[citation needed]

Behavior outside of psychology includes physical property and chemical reactions.

In environmental modeling and especially in hydrology, a "behavioral model" means a model that is acceptably consistent with observed natural processes, i.e., that simulates well, for example, observed river discharge. It is a key concept of the so-called Generalized Likelihood Uncertainty Estimation (GLUE) methodology to quantify how uncertain environmental predictions are.

In management, behaviors are associated with desired or undesired focuses. Managers generally note what the desired outcome is, but behavioral patterns can take over. These patterns are the reference to how often the desired behavior actually occurs. Before a behavior actually occurs, antecedents focus on the stimuli that influence the behavior that is about to happen. After the behavior occurs, consequences fall into place. They can come in the form of rewards or punishments.

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Langman’s Medical Embryology: 9781451191646: Medicine …

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Muscular System – Muscles of the Human Body

[Continued from above] . . . Muscular System Anatomy

Muscle Types There are three types of muscle tissue:Visceral, cardiac, and skeletal.

The cells of cardiac muscle tissue are striatedthat is, they appear to have light and dark stripes when viewed under a light microscope. The arrangement of protein fibers inside of the cells causes these light and dark bands. Striations indicate that a muscle cell is very strong, unlike visceral muscles.

The cells of cardiac muscle are branched X or Y shaped cells tightly connected together by special junctions called intercalated disks. Intercalated disks are made up of fingerlike projections from two neighboring cells that interlock and provide a strong bond between the cells. The branched structure and intercalated disks allow the muscle cells to resist high blood pressures and the strain of pumping blood throughout a lifetime. These features also help to spread electrochemical signals quickly from cell to cell so that the heart can beat as a unit.

Skeletal muscle cells form when many smaller progenitor cells lump themselves together to form long, straight, multinucleated fibers. Striated just like cardiac muscle, these skeletal muscle fibers are very strong. Skeletal muscle derives its name from the fact that these muscles always connect to the skeleton in at least one place.

Gross Anatomy of a Skeletal Muscle Most skeletal muscles are attached to two bones through tendons. Tendons are tough bands of dense regular connective tissue whose strong collagen fibers firmly attach muscles to bones. Tendons are under extreme stress when muscles pull on them, so they are very strong and are woven into the coverings of both muscles and bones.

Muscles move by shortening their length, pulling on tendons, and moving bones closer to each other. One of the bones is pulled towards the other bone, which remains stationary. The place on the stationary bone that is connected via tendons to the muscle is called the origin. The place on the moving bone that is connected to the muscle via tendons is called the insertion. The belly of the muscle is the fleshy part of the muscle in between the tendons that does the actual contraction.

Names of Skeletal Muscles Skeletal muscles are named based on many different factors, including their location, origin and insertion, number of origins, shape, size, direction, and function.

Groups Action in Skeletal Muscle Skeletal muscles rarely work by themselves to achieve movements in the body. More often they work in groups to produce precise movements. The muscle that produces any particular movement of the body is known as an agonist or prime mover. The agonist always pairs with an antagonist muscle that produces the opposite effect on the same bones. For example, the biceps brachii muscle flexes the arm at the elbow. As the antagonist for this motion, the triceps brachii muscle extends the arm at the elbow. When the triceps is extending the arm, the biceps would be considered the antagonist.

In addition to the agonist/antagonist pairing, other muscles work to support the movements of the agonist. Synergists are muscles that help to stabilize a movement and reduce extraneous movements. They are usually found in regions near the agonist and often connect to the same bones. Because skeletal muscles move the insertion closer to the immobile origin, fixator muscles assist in movement by holding the origin stable. If you lift something heavy with your arms, fixators in the trunk region hold your body upright and immobile so that you maintain your balance while lifting.

Skeletal Muscle Histology Skeletal muscle fibers differ dramatically from other tissues of the body due to their highly specialized functions. Many of the organelles that make up muscle fibers are unique to this type of cell.

The sarcolemma is the cell membrane of muscle fibers. The sarcolemma acts as a conductor for electrochemical signals that stimulate muscle cells. Connected to the sarcolemma are transverse tubules (T-tubules) that help carry these electrochemical signals into the middle of the muscle fiber. The sarcoplasmic reticulum serves as a storage facility for calcium ions (Ca2+) that are vital to muscle contraction. Mitochondria, the power houses of the cell, are abundant in muscle cells to break down sugars and provide energy in the form of ATP to active muscles. Most of the muscle fibers structure is made up of myofibrils, which are the contractile structures of the cell. Myofibrils are made up of many proteins fibers arranged into repeating subunits called sarcomeres. The sarcomere is the functional unit of muscle fibers. (See Macronutrients for more information about the roles of sugars and proteins.)

Sarcomere Structure Sarcomeres are made of two types of protein fibers: thick filaments and thin filaments.

Function of Muscle Tissue The main function of the muscular system is movement. Muscles are the only tissue in the body that has the ability to contract and therefore move the other parts of the body.

Related to the function of movement is the muscular systems second function: the maintenance of posture and body position. Muscles often contract to hold the body still or in a particular position rather than to cause movement. The muscles responsible for the bodys posture have the greatest endurance of all muscles in the bodythey hold up the body throughout the day without becoming tired.

Another function related to movement is the movement of substances inside the body. The cardiac and visceral muscles are primarily responsible for transporting substances like blood or food from one part of the body to another.

The final function of muscle tissue is the generation of body heat. As a result of the high metabolic rate of contracting muscle, our muscular system produces a great deal of waste heat. Many small muscle contractions within the body produce our natural body heat. When we exert ourselves more than normal, the extra muscle contractions lead to a rise in body temperature and eventually to sweating.

Skeletal Muscles as Levers Skeletal muscles work together with bones and joints to form lever systems. The muscle acts as the effort force; the joint acts as the fulcrum; the bone that the muscle moves acts as the lever; and the object being moved acts as the load.

There are three classes of levers, but the vast majority of the levers in the body are third class levers. A third class lever is a system in which the fulcrum is at the end of the lever and the effort is between the fulcrum and the load at the other end of the lever. The third class levers in the body serve to increase the distance moved by the load compared to the distance that the muscle contracts.

The tradeoff for this increase in distance is that the force required to move the load must be greater than the mass of the load. For example, the biceps brachia of the arm pulls on the radius of the forearm, causing flexion at the elbow joint in a third class lever system. A very slight change in the length of the biceps causes a much larger movement of the forearm and hand, but the force applied by the biceps must be higher than the load moved by the muscle.

Motor Units Nerve cells called motor neurons control the skeletal muscles. Each motor neuron controls several muscle cells in a group known as a motor unit. When a motor neuron receives a signal from the brain, it stimulates all of the muscles cells in its motor unit at the same time.

The size of motor units varies throughout the body, depending on the function of a muscle. Muscles that perform fine movementslike those of theeyes or fingershave very few muscle fibers in each motor unit to improve the precision of the brains control over these structures. Muscles that need a lot of strength to perform their functionlike leg or arm muscleshave many muscle cells in each motor unit. One of the ways that the body can control the strength of each muscle is by determining how many motor units to activate for a given function. This explains why the same muscles that are used to pick up a pencil are also used to pick up a bowling ball.

Contraction Cycle Muscles contract when stimulated by signals from their motor neurons. Motor neurons contact muscle cells at a point called the Neuromuscular Junction (NMJ). Motor neurons release neurotransmitter chemicals at the NMJ that bond to a special part of the sarcolemma known as the motor end plate. The motor end plate contains many ion channels that open in response to neurotransmitters and allow positive ions to enter the muscle fiber. The positive ions form an electrochemical gradient to form inside of the cell, which spreads throughout the sarcolemma and the T-tubules by opening even more ion channels.

When the positive ions reach the sarcoplasmic reticulum, Ca2+ ions are released and allowed to flow into the myofibrils. Ca2+ ions bind to troponin, which causes the troponin molecule to change shape and move nearby molecules of tropomyosin. Tropomyosin is moved away from myosin binding sites on actin molecules, allowing actin and myosin to bind together.

ATP molecules power myosin proteins in the thick filaments to bend and pull on actin molecules in the thin filaments. Myosin proteins act like oars on a boat, pulling the thin filaments closer to the center of a sarcomere. As the thin filaments are pulled together, the sarcomere shortens and contracts. Myofibrils of muscle fibers are made of many sarcomeres in a row, so that when all of the sarcomeres contract, the muscle cells shortens with a great force relative to its size.

Muscles continue contraction as long as they are stimulated by a neurotransmitter. When a motor neuron stops the release of the neurotransmitter, the process of contraction reverses itself. Calcium returns to the sarcoplasmic reticulum; troponin and tropomyosin return to their resting positions; and actin and myosin are prevented from binding. Sarcomeres return to their elongated resting state once the force of myosin pulling on actin has stopped.

Types of Muscle Contraction The strength of a muscles contraction can be controlled by two factors: the number of motor units involved in contraction and the amount of stimulus from the nervous system. A single nerve impulse of a motor neuron will cause a motor unit to contract briefly before relaxing. This small contraction is known as a twitch contraction. If the motor neuron provides several signals within a short period of time, the strength and duration of the muscle contraction increases. This phenomenon is known as temporal summation. If the motor neuron provides many nerve impulses in rapid succession, the muscle may enter the state of tetanus, or complete and lasting contraction. A muscle will remain in tetanus until the nerve signal rate slows or until the muscle becomes too fatigued to maintain the tetanus.

Not all muscle contractions produce movement. Isometric contractions are light contractions that increase the tension in the muscle without exerting enough force to move a body part. When people tense their bodies due to stress, they are performing an isometric contraction. Holding an object still and maintaining posture are also the result of isometric contractions. A contraction that does produce movement is an isotonic contraction. Isotonic contractions are required to develop muscle mass through weight lifting.

Muscle tone is a natural condition in which a skeletal muscle stays partially contracted at all times. Muscle tone provides a slight tension on the muscle to prevent damage to the muscle and joints from sudden movements, and also helps to maintain the bodys posture. All muscles maintain some amount of muscle tone at all times, unless the muscle has been disconnected from the central nervous system due to nerve damage.

Functional Types of Skeletal Muscle Fibers Skeletal muscle fibers can be divided into two types based on how they produce and use energy: Type I and Type II.

Muscle Metabolism and Fatigue Muscles get their energy from different sources depending on the situation that the muscle is working in. Muscles use aerobic respiration when we call on them to produce a low to moderate level of force. Aerobic respiration requires oxygen to produce about 36-38 ATP molecules from a molecule of glucose. Aerobic respiration is very efficient, and can continue as long as a muscle receives adequate amounts of oxygen and glucose to keep contracting. When we use muscles to produce a high level of force, they become so tightly contracted that oxygen carrying blood cannot enter the muscle. This condition causes the muscle to create energy using lactic acid fermentation, a form of anaerobic respiration. Anaerobic respiration is much less efficient than aerobic respirationonly 2 ATP are produced for each molecule of glucose. Muscles quickly tire as they burn through their energy reserves under anaerobic respiration.

To keep muscles working for a longer period of time, muscle fibers contain several important energy molecules. Myoglobin, a red pigment found in muscles, contains iron and stores oxygen in a manner similar to hemoglobin in the blood. The oxygen from myoglobin allows muscles to continue aerobic respiration in the absence of oxygen. Another chemical that helps to keep muscles working is creatine phosphate. Muscles use energy in the form of ATP, converting ATP to ADP to release its energy. Creatine phosphate donates its phosphate group to ADP to turn it back into ATP in order to provide extra energy to the muscle. Finally, muscle fibers contain energy-storing glycogen, a large macromolecule made of many linked glucoses. Active muscles break glucoses off of glycogen molecules to provide an internal fuel supply.

When muscles run out of energy during either aerobic or anaerobic respiration, the muscle quickly tires and loses its ability to contract. This condition is known as muscle fatigue. A fatigued muscle contains very little or no oxygen, glucose or ATP, but instead has many waste products from respiration, like lactic acid and ADP. The body must take in extra oxygen after exertion to replace the oxygen that was stored in myoglobin in the muscle fiber as well as to power the aerobic respiration that will rebuild the energy supplies inside of the cell. Oxygen debt (or recovery oxygen uptake) is the name for the extra oxygen that the body must take in to restore the muscle cells to their resting state. This explains why you feel out of breath for a few minutes after a strenuous activityyour body is trying to restore itself to its normal state.

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Should I stay or should I go? On the importance of aversive memories and the endogenous cannabinoid system

Memory is not a simple box of souvenirs; it is also, and most importantly, a safety system for organisms. With the help of negative memories, known as aversive memories, we can avoid a threat that we have already confronted. Researchers from Inserm and University of Bordeaux have just discovered that the cannabinoid receptors of the brain control these memories that are crucial for survival. This study is published in Neuron.

When confronted by danger, every individual has to make a crucial choice. This type of simple decision may determine his/her destiny: if the fire alarm goes off, we have learned to heed it and flee, and not to ignore it. In the same way, we avoid food and drinks that might have made us sick in the past.

The body is thus equipped with neurological mechanisms that help it to adjust its behaviour in response to a stimulus. Such is the case with aversive memories, a key survival process, which prepares the body to avoid these potential dangers effectively. These memories are accompanied by physiological responses (fright and flight) that enable one to get away from a dangerous situation.

Although the role of the habenula, a central region of the brain, in this phenomenon has received a great deal of attention in recent years, the same is not true of the endogenous cannabinoid system of the habenular neurons, on which Giovanni Marsicano and his team (particularly Edgar Soria-Gomez) have focused. This system involves the type 1 cannabinoid receptors. These receptors, the activity of which is normally regulated by endocannabinoids the bodys own molecules are the target of the main psychoactive components of cannabis.

The researchers conditioned mice so that they reacted to certain danger signals (sounds or smells). When they exposed them to these signals, mice that were deficient in cannabinoid receptors in the habenula expressed neither the fear nor the repulsion observed in normal mice. Interestingly, this impaired reaction did not apply to neutral or positive memories, which remained unchanged in these mice.

At molecular level, the scientists observed that, although the functioning of the habenula normally involves two molecules (acetylcholine and glutamate), the defect observed in these mice is caused by an imbalance in neurotransmission involving only acetylcholine.

These results demonstrate that the endogenous cannabinoid system in the habenula exclusively controls the expression of aversive memories, without influencing neutral or positive memories, and does so by selectively modulating acetylcholine in the neural circuits involved, explains Giovanni Marsicano, Inserm Research Director.

The control of these particular memories is an integral part of diseases associated with the emotional process, such as depression, anxiety or drug addiction. As a consequence, the endogenous cannabinoid system of the habenula might represent a new therapeutic target in the management of these conditions.

Filed under memory habenula endocannabinoids cannabinoid system acetylcholine neuroscience science

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Stem Cell Research Hints at Evolution of Human Brain

The human cerebral cortex contains 16 billion neurons, wired together into arcane, layered circuits responsible for everything from our ability to walk and talk to our sense of nostalgia and drive to dream of the future. In the course of human evolution, the cortex has expanded as much as 1,000-fold, but how this occurred is still a mystery to scientists.

Now, researchers at UC San Francisco have succeeded in mapping the genetic signature of a unique group of stem cells in the human brain that seem to generate most of the neurons in our massive cerebral cortex.

The new findings, published Sept. 24 in the journal Cell, support the notion that these unusual stem cells may have played an important role in the remarkable evolutionary expansion of the primate brain.

We want to know what it is about our genetic heritage that makes us unique, said Arnold Kriegstein, MD, PhD, professor of developmental and stem cell biology and director of the Eli and Edyth Broad Center of Regeneration Medicine and Stem Cell Research at UCSF. Looking at these early stages in development is the best opportunity to understand our brains evolution.

Building a Brain from the Inside Out

The grand architecture of the human cortex, with its hundreds of distinct cell types, begins as a uniform layer of neural stem cells and builds itself from the inside out during several months of embryonic development.

Until recently, most of what scientists knew about this process came from studies of model organisms such as mice, where nearly all neurons are produced by stem cells called ventricular radial glia (vRGs) that inhabit a fertile layer of tissue deep in the brain called the ventricular zone (VZ). But recent insights suggested that the development of the human cortex might have some additional wrinkles.

In 2010, Kriegsteins lab discovered a new type of neural stem cell in the human brain, which they dubbed outer radial glia (oRGs) because these cells reside farther away from the nurturing ventricles, in an outer layer of the subventricular zone (oSVZ). To the researchers surprise, further investigations revealed that during the peak of cortical development in humans, most of the neuron production was happening in the oSVZ rather than the familiar VZ.

oRG stem cells are extremely rare in mice, but common in primates, and look and behave quite differently from familiar ventricular radial glia. Their discovery immediately made Kriegstein and colleagues wonder whether this unusual group of stem cells could be a key to understanding what allowed primate brains to grow to their immense size and complexity.

We wanted to know more about the differences between these two different stem cell populations, said Alex Pollen, PhD, a postdoctoral researcher in Kriegsteins lab and co-lead author of the new study. We predicted oRGs could be a major contributor to the development of the human cortex, but at first we only had circumstantial evidence that these cells even made neurons.

Outsider Stem Cells Make Their Own Niche

In the new research, Pollen and co-first author Tomasz Nowakowski, PhD, also a postdoctoral researcher in the Kriegstein lab, partnered with Fluidigm Corp. to develop a microfluidic approach to map out the transcriptional profile the set of genes that are actively producing RNA of cells collected from the VZ and SVZ during embryonic development.

They identified gene expression profiles typical of different types of neurons, newborn neural progenitors and radial glia, as well as molecular markers differentiating oRGs and vRGs, which allowed the researchers to isolate these cells for further study.

The gene activity profiles also provided several novel insights into the biology of outer radial glia. For example, researchers had previously been puzzled as to how oRG cells could maintain their generative vitality so far away from the nurturing VZ. In the mouse, as cells move away from the ventricles, they lose their ability to differentiate into neurons, Kriegstein explained.

But the new data reveals that oRGs bring a support group with them: The cells express genes for surface markers and molecular signals that enhance their own ability to proliferate, the researchers found.

This is a surprising new feature of their biology, Pollen said. They generate their own stem cell niche.

The researchers used their new molecular insights to isolate oRGs in culture for the first time, and showed that these cells are prolific neuron factories. In contrast to mouse vRGs, which produce 10 to 100 daughter cells during brain development, a single human oRG can produce thousands of daughter neurons, as well as glial cellsnon-neuronal brain cells increasingly recognized as being responsible for a broad array of maintenance functions in the brain.

New Insights into Brain Evolution, Development and Disease

The discovery of human oRGs self-renewing niche and remarkable generative capacity reinforces the idea that these cells may have been responsible for the expansion of the cerebral cortex in our primate ancestors, the researchers said.

The research also presents an opportunity to greatly improve techniques for growing brain circuits in a dish that reflect the true diversity of the human brain, they said. Such techniques have the potential to enhance research into the origins of neurodevelopmental and neuropsychiatric disorders such as microcephaly, lissencephaly, autism and schizophrenia, which are thought to affect cell types not found in the mouse models that are often used to study such diseases.

The findings may even have implications for studying glioblastoma, a common brain cancer whose ability to grow, migrate and hack into the brains blood supply appears to rely on a pattern of gene activity similar to that now identified in these neural stem cells.

The cerebral cortex is so different in humans than in mice, Kriegstein said. If youre interested in how our brains evolved or in diseases of the cerebral cortex, this is a really exciting discovery.

The study represents the first salvo of a larger BRAIN Initiative-funded project in Kriegsteins lab to understand the thousands of different cell types that occupy the developing human brain

At the moment, we simply dont have a good understanding of the brains parts list, Kriegstein said, but studies like this are beginning to give us a real blueprint of how our brains are built.

Filed under stem cells radial glia glial cells cerebral cortex evolution gene expression neuroscience science

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Reproducible neuroscience with real tango Consonant results resonate in the brain

Most neuroscientific studies rely on a single experiment and assume their findings to be reliable. However, the validity of this assumption needs to be tested before accepting the findings as the ground truth. Indeed, the lack of replication studies in addition to the inconsistency of neuroimaging findings severely limits the advancement of knowledge in the field of neuroscience, all of which has recently become a hot topic within the neuroscientific community.

Concerned about this state of affairs, researchers at the Finnish Centre for Interdisciplinary Music Research (CIMR), University of Jyvskyl, in Finland, and from Aarhus University, in Denmark, aimed to replicate previous findings on how the brain processes music using a novel, naturalistic free listening context. Their results, published in Neuroimage, demonstrate that laboratory conditions resembling real-life contexts can yield reliable results, making findings more ecologically valid. The more we can simulate reality in a lab in a reliable way, the more truetolife the findings will be, and this is critical to modelling the way the brain actually understands the world, sums up Doctoral Student Iballa Burunat, the lead author of the study.

The research team employed an identical methodology as in the original study, but using a new group of participants. As in the original study, participants had to just listen to the musical piece Adis Nonino by A. Piazzolla. Researchers assessed how similar the observed brain activity was between the original and the new study. Replicating the experiment allowed the researchers to fine-tune the findings of the previous study, concluding what brain areas are involved in the processing of different musical elements, like tonality, timbre, and rhythm, and how accurately the neural correlates could be replicated for each of these musical elements. For instance, they observed that highlevel musical features, such as tonality and rhythm, were less replicable than lowlevel (timbral) ones. One reason for this may be that the neural processing of highlevel musical features is more sensitive to state and traits of the listeners compared to the processing of lowlevel features, which may hinder the replication of previous findings, says Academy Professor Petri Toiviainen, from the University of Jyvskyl, a co-author of the study.

When listening to a piece of music, we cant separate its auditory characteristics from its affective, cognitive, and contextual dimensions. It is precisely the integration of all these aspects that gives coherence to our listening experience. This is why taking a more naturalistic approach makes neuroscience more faithful to reality, a goal that a fully controlled setting that uses very simple and artificially created sounds falls short of. The success in replicating these findings should encourage scientists to move towards more reallife paradigms that capture the complexity of the real world.

The neuroscientific community needs to challenge the current scientific model driven by dysfunctional research practices tacitly encouraged by the publish or perish doctrine, which is precisely leading to the low reliability and the high discrepancy of results, states Iballa Burunat. The authors stress that more incentives are needed for replicating experiments, and agree that scientific journals should more often than not welcome replication studies to ensure that published research is robust and reliable.

Filed under brain activity neuroimaging music neuroscience science

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(Image caption: Lateral view of the Paranthropus robustus skull SK 46 from the site of Swartkrans, South Africa showing the 3D virtual reconstruction of the ear and the hearing results for the early hominins. Credit: Rolf Quam)

2-Million-Year-Old Fossils Reveal Hearing Abilities of Early Humans

Research into human fossils dating back to approximately two million years ago reveals that the hearing pattern resembles chimpanzees, but with some slight differences in the direction of humans.

Rolf Quam, assistant professor of anthropology at Binghamton University, led an international research team in reconstructing an aspect of sensory perception in several fossil hominin individuals from the sites of Sterkfontein and Swartkrans in South Africa. The study relied on the use of CT scans and virtual computer reconstructions to study the internal anatomy of the ear. The results suggest that the early hominin species Australopithecus africanus and Paranthropus robustus, both of which lived around 2 million years ago, had hearing abilities similar to a chimpanzee, but with some slight differences in the direction of humans.

Humans are distinct from most other primates, including chimpanzees, in having better hearing across a wider range of frequencies, generally between 1.0-6.0 kHz. Within this same frequency range, which encompasses many of the sounds emitted during spoken language, chimpanzees and most other primates lose sensitivity compared to humans.

We know that the hearing patterns, or audiograms, in chimpanzees and humans are distinct because their hearing abilities have been measured in the laboratory in living subjects, said Quam. So we were interested in finding out when this human-like hearing pattern first emerged during our evolutionary history.

Previously, Quam and colleagues studied the hearing abilities in several fossil hominin individuals from the site of the Sima de los Huesos (Pit of the Bones) in northern Spain. These fossils are about 430,000 years old and are considered to represent ancestors of the later Neandertals. The hearing abilities in the Sima hominins were nearly identical to living humans. In contrast, the much earlier South African specimens had a hearing pattern that was much more similar to a chimpanzee.

In the South African fossils, the region of maximum hearing sensitivity was shifted towards slightly higher frequencies compared with chimpanzees, and the early hominins showed better hearing than either chimpanzees or humans from about 1.0-3.0 kHz. It turns out that this auditory pattern may have been particularly favorable for living on the savanna. In more open environments, sound waves dont travel as far as in the rainforest canopy, so short range communication is favored on the savanna.

We know these species regularly occupied the savanna since their diet included up to 50 percent of resources found in open environments said Quam. The researchers argue that this combination of auditory features may have favored short-range communication in open environments.

That sounds a lot like language. Does this mean these early hominins had language? No, said Quam. Were not arguing that. They certainly could communicate vocally. All primates do, but were not saying they had fully developed human language, which implies a symbolic content.

The emergence of language is one of the most hotly debated questions in paleoanthropology, the branch of anthropology that studies human origins, since the capacity for spoken language is often held to be a defining human feature. There is a general consensus among anthropologists that the small brain size and ape-like cranial anatomy and vocal tract in these early hominins indicates they likely did not have the capacity for language.

We feel our research line does have considerable potential to provide new insights into when the human hearing pattern emerged and, by extension, when we developed language, said Quam.

Ignacio Martinez, a collaborator on the study, said, Were pretty confident about our results and our interpretation. In particular, its very gratifying when several independent lines of evidence converge on a consistent interpretation.

How do these results compare with the discovery of a new hominin species, Homo naledi, announced just two weeks ago from a different site in South Africa?

It would be really interesting to study the hearing pattern in this new species, said Quam. Stay tuned.

The study was published on Sept. 25 in the journal Science Advances.

Filed under hearing evolution australopithecus paranthropus communication neuroscience science

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Of brains and bones: How hunger neurons control bone mass

In an advance that helps clarify the role of a cluster of neurons in the brain, Yale School of Medicine researchers have found that these neurons not only control hunger and appetite, but also regulate bone mass.

The study is published Sept. 24 online ahead of print in the journal Cell Reports.

We have found that the level of your hunger could determine your bone structure, said one of the senior authors, Tamas L. Horvath, the Jean and David W. Wallace Professor of Comparative Medicine, and professor of neurobiology and obstetrics, gynecology, and reproductive sciences. Horvath is also director of the Yale Program in Integrative Cell Signaling and Neurobiology of Metabolism.

The less hungry you are, the lower your bone density, and surprisingly, the effects of these neurons on bone mass are independent of the effect of the hormone leptin on these same cells.

Horvath and his team focused on agouti-related peptide (AgRP) neurons in the hypothalamus, which control feeding and compulsive behaviors. Using mice that were genetically-engineered so their cells selectively interfere with the AgRP neurons, the team found that these same cells are also involved in determining bone mass.

The team further found that when the AgRP circuits were impaired, this resulted in bone loss and osteopenia in mice the equivalent of osteoporosis in women. But when the team enhanced AgRP neuronal activity in mice, this actually promoted increased bone mass.

Taken together, these observations establish a significant regulatory role for AgRP neurons in skeletal bone metabolism independent of leptins action, said co-senior author Dr. Karl Insogna, professor of medicine, and director of the Yale Bone Center. Based on our findings, it seems that the effect of AgRP neurons on bone metabolism in adults is mediated at least in part by the sympathetic nervous system, but more than one pathway is likely involved.

There are other mechanisms by which the AgRP system can affect bone mass, including actions on the thyroid, adrenal and gonad systems, Insogna added. Further studies are needed to assess the hormonal control of bone metabolism as a pathway modulated by AgRP neurons.

Filed under AgRP neurons hypothalamus leptin neural circuits bone mass neuroscience science

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From brain, to fat, to weight loss

Weight is controlled by the hormone leptin, which acts in the brain to regulate food intake and metabolism. However, it was largely unknown until now, how the brain signals back to the fat tissue to induce fat breakdown. Now, a breakthrough study led by Ana Domingos at Instituto Gulbenkian de Cincia (IGC; Portugal), in collaboration with Jeffrey Friedmans group at Rockefeller University (USA), has shown that fat tissue is innervated and that direct stimulation of neurons in fat is sufficient to induce fat breakdown. These results, published in the latest issue of the prestigious journal Cell, set up the stage for developing novel anti-obesity therapies.

Fat tissue constitutes 20 to 25% of human body weight being an energy storage container, in the form of triglycerides. Twenty years ago Jeffrey Friedman and colleagues identified the hormone leptin, which is produced by fat cells in amounts that are proportional to the amount of fat, and informs the brain about how much fat is available in the body. Leptin functions as an adipostat neuro-endocrine signal that preserves bodys fat mass in a relatively narrow range of variation. Low leptin levels increase appetite and lower basal metabolism, whereas high leptin levels blunt appetite and promote fat breakdown. However, until now it was largely unknown what circuits close the neuroendocrine loop, such that leptin action in the brain signals back to the fat.

Now, the research team led by Ana Domingos, combined a variety of techniques to functionally establish, for the first time, that white fat tissue is innervated. We dissected these nerve fibers from mouse fat, and using molecular markers identified these as sympathetic neurons, explains Ana Domingos. But most remarkable, when we used an ultra sensitive imaging technique, on the intact white fat tissue of a living mouse, we observed that fat cells can be encapsulated by these sympathetic neural terminals.

Next, researchers used genetic engineered mice, whose sympathetic neurons could be activated by blue light, to assess the functional relevance of these fat projecting neurons. Roksana Pirzgalska, a doctorate student in Domingos laboratory and co-first author of the study explains: We used a powerful technique called optogenetics, to locally activate these sympathetic neurons in fat pads of mice, and observed fat breakdown and fat mass reduction. Ana Domingos adds: The local activation of these neurons, leads to the release of norepinephrine, a neurotransmitter, that triggers a cascade of signals in fat cells leading to fat hydrolysis. Without these neurons, leptin is unable to drive fat-breakdown. The conclusions and future directions are clear according to Ana Domingos: This result provides new hopes for treating central leptin resistance, a condition in which the brains of obese people are insensitive to leptin. Senior co-author Jeffrey Friedman adds: These studies add an important new piece to the puzzle that enables leptin to induce fat loss.

Filed under leptin fat tissue weight loss neurons lipolysis neuroscience science

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Liquid crystals are familiar to most of us as the somewhat humdrum stuff used to make computer displays and TVs. Even for scientists, it has not been easy to find other uses.

(Image caption: These magnified images show how untreated liquid crystals (top) respond to the human islet amyloid peptide (lower right), which forms aggregates and is involved in diabetes; and rat islet amyloid (lower left), which does not aggregate. The actual width of these panels is 280 microns, approximately the diameter of several human hairs lying side by side. Credit: Courtesy of Advanced Functional Materials, Sadati and others)

Now a group of researchers at the University of Chicagos Institute for Molecular Engineering is putting liquid crystals to work in a completely unexpected realm: as detectors for the protein fibers implicated in the development of neuro-degenerative diseases such as Alzheimers. Their novel approach promises an easier, less costly way to detect these fibers and to do so at a much earlier stage of their formation than has been possible beforethe stage when they are thought to be the most toxic.

It is extremely important to develop techniques that allow us to detect the formation of these so-called amyloid fibrils when theyre first starting to grow, said Juan de Pablo, whose group did the new work. We have developed a system that allows us to detect them in a simple and inexpensive manner. And the sensitivity appears to be extremely high.

Amyloid fibrils are protein aggregates that are associated with the development of neuro-degenerative diseases, including Huntingtons, Parkinsons, Alzheimers and mad cow disease, as well as in Type 2 diabetes, where they damage the pancreatic islets. Scientists would like to be able to study their formation both for therapeutic reasons and so they can test the effect of new drugs on inhibiting their growth. But the fibrils that are believed to be most harmful are too tiny to be seen using an optical microscope. So scientists have relied on elaborate and expensive fluorescence- or neutron scattering-based techniques to study them.

A different approach

The de Pablo group took a completely different approach. They exploited the way a liquid crystal responds to a disturbance on its surface. The scientists made a film of a liquid crystal molecule called 5CB, which de Pablo calls the fruit fly of liquid crystal research because it is so well studied. Then they applied chemicals to the 5CB film that caused the molecules to align in such a way as to block the passage of light. Floating on top of the film was a membrane made of molecules resembling those found in the membranes of biological cells. And on top of that was water, into which the scientists injected the molecules that spontaneously form the toxic aggregates.

As aggregates grow on the membrane, they imprint their shape into the liquid crystal underneath, said de Pablo, the Liew Family Professor in Molecular Engineering. The liquid crystal molecules that are at the interface become distorted: they adopt a different orientation, so that light can now go through.

This disturbance on the membranethe imprint of the protein fibersis transmitted down through the liquid crystal film, in effect amplifying it.

The fibers might be tens of nanometers in diameter and a hundred nanometers long, far smaller than a red blood cell. But the disturbance they create is magnified by the liquid crystal so that it is large enough to be seen in polarized light with a simple optical microscope.

Microscopic bright spots

Seen through the microscope, the aggregates appear as tiny bright spots in a sea of black: bright where the liquid crystal has been disturbed to let light pass. The liquid crystal is actually reporting whats happening to the aggregates at the interface, de Pablo said. And these bright spots become bigger and adopt the shape of the actual fibers that the protein is forming. Except youre not seeing the fibers, youre seeing the liquid crystals response to the fibers.

The work of de Pablos team was published online Sept. 9, 2015, by the journal Advanced Functional Materials. Co-authoring the article were IME scientists Monirosadat Sadati, Julio Armas-Perez, Jose Martinez-Gonzalez, and Juan Hernandez-Ortiz, as well as Aslin Izmitli-Apik and Nicholas Abbott of the University of Wisconsin at Madison.

They relied crucially on theoretical molecular models, both to help guide them through the real system and to help them understand what they were seeing. They are now developing sensors for the amyloid fibrils that may allow experimenters to use droplets of liquid crystals in emulsion rather than the flat surfaces used in the proof-of-concept experiments.

That, said de Pablo, would be a lot easier for people to use. He envisions scientists eventually being able to test small samples of blood or other body fluid using the new detectors, or for drug researchers to put the amyloid proteins in water, inject their drug, and study how the drug influences the growth of the aggregates over time.

For research in Type 2 diabetes, or Alzheimers or Parkinsons, having this simple platform to perform these tests at a fraction of the cost of whats required for fluorescence or neutron scattering would be very useful.

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Neuroscience

Affective neuroscience – Wikipedia, the free encyclopedia

Affective neuroscience is the study of the neural mechanisms of emotion. This interdisciplinary field combines neuroscience with the psychological study of personality, emotion, and mood.[1]

Emotions are thought to be related to activity in brain areas that direct our attention, motivate our behavior, and determine the significance of what is going on around us. Pioneering work by Paul Broca (1878),[2]James Papez (1937),[3] and Paul D. MacLean (1952)[4] suggested that emotion is related to a group of structures in the center of the brain called the limbic system, which includes the hypothalamus, cingulate cortex, hippocampi, and other structures. Research has shown that limbic structures are directly related to emotion, but non-limbic structures have been found to be of greater emotional relevance. The following brain structures are currently thought to be involved in emotion:[5]

The Right Hemisphere has been proposed over time as being directly involved in the processing of emotion. Scientific theory regarding the role of the right hemisphere has developed over time and resulted in several models of emotional functioning. C.K. Mills was one of the first researchers to propose a direct link between the right hemisphere and emotional processing, having observed decreased emotional processing in patients with lesions to the right hemisphere.[26][27] Emotion was originally thought to be processed in the limbic system structures such as the hypothalamus and amygdala.[28] As of the late 1980s to early 1990s however, neocortical structures were shown to have an involvement in emotion.[29] These findings led to the development of the Right Hemisphere Hypothesis and the Valence Hypothesis.

The Right Hemisphere Hypothesis asserts that the right hemisphere of the neocortical structures is specialized for the expression and perception of emotion.[30] The Right hemisphere has been linked with mental strategies that are nonverbal, synthetic, integrative, holistic, and Gestalt which makes it ideal for processing emotion.[29] The right hemisphere is more in touch with subcortical systems of autonomic arousal and attention as demonstrated in patients that have increased spatial neglect when damage is associated to the right brain as opposed to the left brain.[31] Right hemisphere pathologies have also been linked with abnormal patterns of autonomic nervous system responses.[32] These findings would help signify the relationship of the subcortical brain regions to the right hemisphere as having a strong connection.

The Valence Hypothesis acknowledges the right hemisphere's role in emotion, but asserts that it is mainly focused on the processing of negative emotions whereas the left hemisphere processes positive emotions. The mode of processing of the two hemispheres has been the discussion of much debate. One version suggests the lack of a specific mode of processes, stating that the right hemisphere is solely negative emotion and the left brain is solely positive emotion.[33] A second version suggests that there is a complex mode of processing that occurs, specifically that there is a hemispheric specialization for the expressing and experiencing of emotion, with the right hemisphere predominating in the experiencing of both positive and negative emotion.[34][35] More recently, the frontal lobe has been the focus of a large amount of research, stating that the frontal lobes of both hemispheres are involved in the emotional state, while the right posterior hemisphere, the parietal and temporal lobes, is involved in the processing of emotion.[36] Decreased right parietal lobe activity has been associated with depression[37] and increased right parietal lobe activity with anxiety arousal.[38] The increasing understanding of the role the different hemispheres play has led to increasingly complicated models, all based some way on the original valence model.[39]

In its broadest sense, cognition refers to all mental processes. However, the study of cognition has historically excluded emotion and focused on non-emotional processes (e.g., memory, attention, perception, action, problem solving and mental imagery).[40] As a result, the study of the neural basis of non-emotional and emotional processes emerged as two separate fields: cognitive neuroscience and affective neuroscience. The distinction between non-emotional and emotional processes is now thought to be largely artificial, as the two types of processes often involve overlapping neural and mental mechanisms.[41] Thus, when cognition is taken at its broadest definition, affective neuroscience could also be called the cognitive neuroscience of emotion.

The emotion go/no-go task has been frequently used to study behavioral inhibition, particularly emotional modulation of this inhibition.[42] A derivation of the original go/no-go paradigm, this task involves a combination of affective go cues, where the participant must make a motor response as quickly as possible, and affective no-go cues, where a response must be withheld. Because go cues are more common, the task is able to measure ones ability to inhibit a response under different emotional conditions.[43]

The task is common in tests of emotion regulation, and is often paired with neuroimaging measures to localize relevant brain function in both healthy individuals and those with affective disorders.[42][44][45] For example, go/no-go studies converge with other methodology to implicate areas of the prefrontal cortex during inhibition of emotionally valenced stimuli.[46]

The emotional Stroop task, an adaptation to the original Stroop, measures attentional bias to emotional stimuli.[47][48] Participants must name the ink color of presented words while ignoring the words themselves.[49] In general, participants have more difficulty detaching attention from affectively valenced words, than neutral words.[50][51] This interference from valenced words is measured by the response latency in naming the color of neutral words as compared with emotional words.[48]

This task has been often used to test selective attention to threatening and other negatively valenced stimuli, most often in relation to psychopathology.[52] Disorder specific attentional biases have been found for a variety of mental disorders.[52][53] For example, participants with spider phobia show a bias to spider-related words but not other negatively valenced words.[54] Similar findings have been attributed to threat words related to other anxiety disorders.[52] However, other studies have questioned these findings. In fact, anxious participants in some studies show the Stroop interference effect for both negative and positive words, when the words are matched for emotionality.[55][56] This means that the specificity effects for various disorders may be largely attributable to the semantic relation of the words to the concerns of the disorder, rather than simply the emotionality of the words.[52]

The Ekman faces task is used to measure emotion recognition of six basic emotions.[57][58] Black and white photographs of 10 actors (6 male, 4 female) are presented, with each actor displaying each basic emotion. Participants are usually asked to respond quickly with the name of the displayed emotion. The task is a common tool to study deficits in emotion regulation in patients with dementia, Parkinson's, and other cognitively degenerative disorders.[59] However, the task has also been used to analyze recognition errors in disorders such as borderline personality disorder, schizophrenia, and bipolar disorder.[60][61][62]

The emotional dot-probe paradigm is a task used to assess selective visual attention to and failure to detach attention from affective stimuli.[63][64] The paradigm begins with a fixation cross at the center of a screen. An emotional stimulus and a neutral stimulus appear side by side, after which a dot appears behind either the neutral stimulus (incongruent condition) or the affective stimulus (congruent condition). Participants asked to indicate when they see this dot, and response latency is measured. Dots that appear on the same side of the screen as the image the participant was looking at will be identified more quickly. Thus, it is possible to discern which object the participant was attending to by subtracting the reaction time to respond to congruent versus incongruent trials.[63]

The best documented research with the dot probe paradigm involves attention to threat related stimuli, such as fearful faces, in individuals with anxiety disorders. Anxious individuals tend to respond more quickly to congruent trials, which may indicate vigilance to threat and/or failure to detach attention from threatening stimuli.[63][65] A specificity effect of attention has also been noted, with individuals attending selectively to threats related to their particular disorder. For example, those with social phobia selectively attend to social threats but not physical threats.[66] However, this specificity may be even more nuanced. Participants with obsessive-compulsive disorder symptoms initially show attentional bias to compulsive threat, but this bias is attenuated in later trials due to habituation to the threat stimuli.[67]

Fear-potentiated startle (FPS) has been utilized as a psychophysiological index of fear reaction in both animals and humans.[68] FPS is most often assessed through the magnitude of the eyeblink startle reflex, which can be measured by electromyography.[69] This eyeblink reflex is an automatic defensive reaction to an abrupt elicitor, making it an objective indicator of fear.[70] Typical FPS paradigms involve bursts of noise or abrupt flashes of light transmitted while an individual attends to a set of stimuli.[70] Startle reflexes have been shown to be modulated by emotion. For example, healthy participants tend to show enhanced startle responses while viewing negatively valenced images and attenuated startle while viewing positively valenced images, as compared with neutral images.[71][72]

The startle response to a particular stimulus is greater under conditions of threat.[73] A common example given to indicate this phenomenon is that ones startle response to a flash of light will be greater when walking in a dangerous neighborhood at night than it would under safer conditions. In laboratory studies, the threat of receiving shock is enough to potentiate startle, even without any actual shock.[74]

Fear potentiated startle paradigms are often used to study fear learning and extinction in individuals with posttraumatic stress disorder and other anxiety disorders.[75][76][77] In fear conditioning studies, an initially neutral stimulus is repeatedly paired with an aversive one, borrowing from classical conditioning.[78] FPS studies have demonstrated that PTSD patients have enhanced startle responses during both danger cues and neutral/safety cues as compared with healthy participants.[78][79]

There are many ways affect plays a role during learning. Recently, affective neuroscience has done much to discover this role. Deep, emotional attachment to a subject area allows a deeper understanding of the material and therefore, learning occurs and lasts.[80] When reading, the emotions one is feeling in comparison to the emotions being portrayed in the content affects ones comprehension. Someone who is feeling sad will understand a sad passage better than someone feeling happy.[81] Therefore, a students emotion plays a big role during the learning process.

Emotion can also be embodied or perceived from words read on a page or a persons facial expression. Neuroimaging studies using fMRI have demonstrated that the same area of the brain being activated when one is feeling disgust is also activated when one observes another person feeling disgust.[82] In a traditional learning environment, the teacher's facial expression can play a critical role in students' language acquisition. Showing a fearful facial expression when reading passages that contain fearful tones facilitates students learning of the meaning of certain vocabulary words and comprehension of the passage.[83]

A meta-analysis is a statistical approach to synthesizing results across multiple studies. Several meta-analyses examining the brain basis of emotion have been conducted. In each meta-analysis, studies were included that investigate healthy, unmedicated adults and that used subtraction analysis to examine the areas of the brain that were more active during emotional processing that during a neutral control condition. The meta-analyses to date predominantly focus on two theoretical approaches, locationist approaches and psychological construction approaches.

These approaches to emotion hypothesize that several emotion categories (including happiness, sadness, fear, anger, and disgust) are biologically basic.[84][85] In this view, emotions are inherited biologically based modules that cannot be broken down into more basic psychological components.[84][85][86] Models following a locationist approach to emotion hypothesize that all mental states belonging to a single emotional category can be consistently and specifically localized to either a distinct brain region or a defined networks of brain regions.[85][87] Each basic emotion category also shares other universal characteristics: distinct facial behavior, physiology, subjective experience and accompanying thoughts and memories.[84]

This approach to emotion hypothesizes that emotions like happiness, sadness, fear, anger and disgust (and many others) are constructed mental states that occur when many different systems in the brain work together.[88] In this view, networks of brain regions underlie psychological operations (e.g., language, attention, etc.) that interact to produce many different kinds of emotion, perception, and cognition.[89] One psychological operation critical for emotion is the network of brain regions that underlie valence (feeling pleasant/unpleasant) and arousal (feeling activated and energized).[88] Emotions emerge when neural systems underlying different psychological operations interact (not just those involved in valence and arousal), producing distributed patterns of activation across the brain. Because emotions emerge from more basic components, there is heterogeneity within each emotion category; for example, a person can experience many different kinds of fear, which feel differently, and which correspond to different neural patterns in the brain. Thus, this view presents a different approach to understanding the neural bases of emotion than locationist approaches.

In the first neuroimaging meta-analysis of emotion, Phan et al. (2002) analyzed the results of 55 studies published in peer reviewed journal articles between January 1990 and December 2000 to determine if the emotions of fear, sadness, disgust, anger, and happiness were consistently associated with activity in specific brain regions. All studies used fMRI or PET techniques to investigate higher-order mental processing of emotion (studies of low-order sensory or motor processes were excluded). The authors analysis approach was to tabulate the number of studies that reported activation in specific brain regions during tasks inducing fear, sadness, disgust, anger, and happiness. For each brain region, statistical chi-squared analysis was conducted to determine if the proportion of studies reporting activation during one emotion was significantly higher than the proportion of studies reporting activation during the other emotions. Two regions showed this statistically significant pattern across studies. In the amygdala, 66% of studies inducing fear reported activity in this region, as compared to ~20% of studies inducing happiness, ~15% of studies inducing sadness (with no reported activations for anger or disgust). In the subcallosal cingulate, 46% of studies inducing sadness reported activity in this region, as compared to ~20% inducing happiness and ~20% inducing anger. This pattern of clear discriminability between emotion categories was in fact rare, with a number of other patterns occurring in limbic regions (including amydala, hippocampus, hypothalamus, and orbitofrontal cortex), paralimbic regions (including subcallosal cingulate, medial prefrontal cortex, anterior cingulate cortex, posterior cingulate cortex, insula, and temporal pole), and uni/heteromodal regions (including lateral prefrontal cortex, primary sensorimotor cortex, temporal cortex, cerebellum, and brainstem). Brain regions implicated across discrete emotion included the basal ganglia (~60% of studies inducing happiness and ~60% of studies inducing disgust reported activity in this region) and medial prefrontal cortex (happiness ~60%, anger ~55%, sadness ~40%, disgust ~40%, and fear ~30%).[90]

Murphy, et al. 2003 analyzed 106 peer reviewed journals published between January 1994 and December 2001 to examine the evidence for regional specialization of discrete emotions (fear, disgust, anger, happiness and sadness) across a larger set of studies that Phan et al. Studies included in the meta-analysis measured activity in the whole brain and regions of interest (activity in individual regions of particular interest to the study). 3-D Kolmogorov-Smirnov (KS3) statistics were used to compare rough spatial distributions of 3-D activation patterns to determine if statistically significant activations (consistently activated across studies) were specific to particular brain regions for all emotional categories. This pattern of consistently activated, regionally specific activations was identified in four brain regions: amygdala with fear, insula with disgust, globus pallidus with disgust, and lateral orbitofrontal cortex with anger. The amygdala was consistently activated in ~40% of studies inducing fear, as compared to less than 20% studies inducing happiness, sadness, or anger. The insula was consistently activated in ~ 70% of studies inducing disgust, as compared to sadness (~40%), anger (~20%), fear (~20%), and happiness (~10%). Similar to the insula, the globus pallidus was consistently activated in ~70% of studies inducing disgust, as compared to less than 25% of studies inducing sadness, fear, anger or happiness. The lateral orbitofrontal cortex was consistently activated in over 80% of studies inducing anger, as compared to fear (~30%), sadness (~20%), happiness (< 20%) and disgust (< 20%). Other regions showed different patterns of activation across categories. For example, both the dorsal medial prefrontal cortex and the rostral anterior cingulate cortex showed consistent activity across emotions (happiness ~50%, sadness ~50%, anger ~ 40%, fear ~30%, and disgust ~ 20%).[91]

Barrett, et al. 2006 examined 161 studies published between 1990-2001, subsets of which were analyzed in previous meta-analyses (Phan, et al. 2002 and Murphy et al. 2003). In this review, the authors examined the locationist hypothesis by comparing the consistency and specificity of prior meta-analytic findings specific to each hypothesized basic emotion (fear, anger, sadness, disgust, and happiness). Consistent neural patterns were defined by brain regions showing increased activity for a specific emotion (relative to a neutral control condition), regardless of the method of induction used (for example, visual vs. auditory cue). Specific neural patterns were defined as architecturally separate circuits for one emotion vs. the other emotions (for example, the fear circuit must be discriminable from the anger circuit, although both circuits may include common brain regions). In general, the results supported consistency among the findings of Phan et al. and Murphy et al., but not specificity. Consistency was determined through the comparison of chi-squared analyses that revealed whether the proportion of studies reporting activation during one emotion was significantly higher than the proportion of studies reporting activation during the other emotions. Specificity was determined through the comparison of emotion-category brain-localizations by contrasting activations in key regions that were specific to particular emotions. Increased amygdala activation during fear was the most consistently reported across induction methods (but not specific). Both meta-analyses also reported increased activations in regions of the anterior cingulate cortex during sadness, although this finding was less consistent (across induction methods) and was not specific to sadness. Both meta-analyses also found that disgust was associated with increased activity in the basal ganglia, but these findings were neither consistent nor specific. Neither consistent nor specific activity was observed across the meta-analyses for anger or for happiness. This meta-analysis additionally introduced the concept of the basic, irreducible elements of emotional life as dimensions such as approach and avoidance. This dimensional approach involved in psychological constructionist approaches is further examined in later meta-analyses of Kober et al. 2008 and Lindquist et al. 2012.[88]

Instead of investigating specific emotions, Kober, et al. 2008 reviewed 162 neuroimaging studies published between 1990-2005 to determine if groups of brain regions show consistent patterns of activation during emotional experience (that is, actively experiencing an emotion first-hand) and during emotion perception (that is, perceiving a given emotion as experienced by another). This meta-analysis used multilevel kernal density analysis (MKDA) to examine fMRI and PET studies, a technique that prevents single studies from dominating the results (particularly if they report multiple nearby peaks) and that enables studies with large sample sizes (those involving more participants) to exert more influence upon the results. MKDA was used to establish a neural reference space that includes the set of regions showing consistent increases across all studies (for further discussion of MDKA see Wager et al. 2007).[92] Next, this neural reference space was partitioned into functional groups of brain regions showing similar activation patterns across studies by first using multivariate techniques to determine co-activation patterns and then using data-reduction techniques to define the functional groupings (resulting in six groups). Consistent with a psychological construction approach to emotion, the authors discuss each functional group in terms more basic psychological operations. The first Core Limbic group included the left amygdala, hypothalamus, periaqueductal gray/thalamus regions, and amygdala/ventral striatum/ventral globus pallidus/thalamus regions, which the authors discuss as an integrative emotional center that plays a general role in evaluating affective significance. The second Lateral Paralimbic group included the ventral anterior insula/frontal operculum/right temporal pole/ posterior orbitofrontal cortex, the anterior insula/ posterior orbitofrontal cortex, the ventral anterior insula/ temporal cortex/ orbitofrontal cortex junction, the midinsula/ dorsal putamen, and the ventral striatum /mid insula/ left hippocampus, which the authors suggest plays a role in motivation, contributing to the general valuation of stimuli and particularly in reward. The third Medial Prefrontal Cortex group included the dorsal medial prefrontal cortex, pregenual anterior cingulate cortex, and rostral dorsal anterior cingulate cortex, which the authors discuss as playing a role in both the generation and regulation of emotion. The fourth Cognitive/ Motor Network group included right frontal operculum, the right interior frontal gyrus, and the pre-supplementray motor area/ left interior frontal gyrus, regions that are not specific to emotion, but instead appear to play a more general role in information processing and cognitive control. The fifth Occipital/ Visual Association group included areas V8 and V4 of the primary visual cortex, the medial temporal lobe, and the lateral occipital cortex, and the sixth Medial Posterior group included posterior cingulate cortex and area V1 of the primary visual cortex. The authors suggest that these regions play a joint role in visual processing and attention to emotional stimuli.[93]

Vytal, et al. 2010 examined 83 neuroimaging studies published between 1993-2008 to examine whether neuroimaging evidence supports the idea of biologically discrete, basic emotions (i.e. fear, anger, disgust, happiness, and sadness). Consistency analyses identified brain regions that were associated with a given emotion. Discriminability analyses identified brain regions that were significantly, differentially active when contrasting pairs of discrete emotions. This meta-analysis examined PET or fMRI studies that reported whole brain analyses identifying significant activations for at least one of the five emotions relative to a neutral or control condition. The authors used activation likelihood estimation (ALE) to perform spatially sensitive, voxel-wise (sensitive to the spatial properties of voxels) statistical comparisons across studies. This technique allows for direct statistical comparison between activation maps associated with each discrete emotion. Thus, discriminability between the five discrete emotion categories was assessed on a more precise spatial scale than what had been accomplished in prior meta-analyses. Consistency was first assessed by comparing the ALE map generated across studies for each emotion (for example, the ALE map identifying regions consistently activated by studies inducing fear) to ALE map generated by random permutations. Discriminability was then assessed by pair-wise contrasts of individual emotion ALE maps (for example, fear ALE map vs. anger ALE map; fear ALE map vs. disgust map) across all basic emotions pairings. Consistent and discriminable patterns of neural activation were observed for the five emotional categories. Happiness was consistently associated with activity in 9 regional brain clusters, the largest located in the right superior temporal gyrus. For the first time, happiness was discriminated from the other emotional categories, with the largest clusters of activity specific to happiness (vs. the other emotion categories) located in right superior temporal gyrus and left rostral anterior cingulate cortex. Sadness was consistently associated with 35 clusters (the largest activation cluster located in the left medial frontal gyrus) and was discriminated from the other emotion categories by significantly greater activity in left medial frontal gyrus, right middle temporal gyrus, and right inferior frontal gyrus. Anger was consistently associated with activity in 13 clusters (the largest of which was located in the left inferior frontal gyrus), and was discriminated from the other emotion categories by significantly greater activity in bilateral inferior frontal gyrus, and in right parahippocampal gyrus. Fear was consistently associated with 11 clusters (the largest activation cluster in the left amygdala) and was discriminated from the other emotion categories by significantly greater activity in the left amygdala and left putamen. Disgust was consistently activated with 16 clusters (the largest activation cluster in the right insula/ right inferior frontal gyrus) and was discriminated from the other emotion categories by significantly greater activity in the right putamen and the left insula.[94]

Lindquist, et al. 2012 reviewed 91 PET and fMRI studies published between January 1990 and December 2007. The studies included in this meta-analysis used induction methods that elicit emotion experience or emotion perception of fear, sadness, disgust, anger, and happiness. The goal was to compare locationist approaches with psychological constructionist approaches to emotion. Similar to Kober et al. described above, a Multilevel Peak Kernel Density Analysis[92] transformed the individual peak activations reported across study contrasts into a neural reference space (in other words, the set of brain regions consistently active across all study contrasts assessing emotion experience or perception). The density analysis was then used to identify regions (or voxels) within the neural reference space with more consistent activations for a specific emotion category (anger, fear, happiness, sadness, and disgust) than all other emotions. Chi-squared analysis was used to create statistical maps that indicated if each previously identified and consistently active regions (those identified during density analysis) were more frequently activated in studies of each emotion category versus the average of all other emotions, regardless of activations elsewhere in the brain. Chi-squared analysis and density analysis both defined functionally consistent and selective regions, or regions which showed a relatively more consistent increase in activity for the experience or perception of one emotion category across studies in the literature. Thus, a selective region could present increased activations relatively more so to one emotion category while also having a response to multiple other emotional categories. A series of logistic regressions were then performed to identify if any of the regions that were identified as consistent and selective to an emotion category were additionally specific to a given category. Regions were defined as specific to a given emotion if they showed increased activations for only one emotional category, and never showed increased activity during instances of the other emotional categories. In other words, a region could be defined as consistent, selective and specific for e.g. fear perception if it only showed significantly greater increases in activation during the perception of fear and did not show increased activity during any other emotion categories. However, the same region would be defined as only consistent and selective (and not specific) to fear perception if it additionally displayed increased activations during anger perception. Strong support for the locationist approach was defined as evidence that basic emotion categories (anger, disgust, fear, happiness and sadness) consistently map onto areas of the brain that specifically activate in response to instances of only one emotional category. Strong support for the constructionist approach was defined as evidence that multiple psychological operations (some of which are not specific or selective to emotion) consistently occur across many brain regions and multiple emotional categories.

The results indicated that many brain regions demonstrated consistent and selective activations in the experience or perception of an emotion category (versus all the other emotion categories). Consistent with constructionist models, however, no region demonstrated functional specificity for the emotions of fear, disgust, happiness, sadness or anger. Based on the existing scientific literature, the authors proposed different roles for the brain regions that have traditionally been associated with only one emotion category. The authors propose that the amygdala, anterior insula, orbitofrontal cortex each contribute to core affect, which are basic feelings that are pleasant or unpleasant with some level of arousal. The amygdala, for example, appears to play a more general role in indicating if external sensory information is motivationally salient, and is particularly active when a stimulus is novel or evokes uncertainty. The anterior insula may represent core affective feelings in awareness across a number of emotion categories, driven largely by sensations originating in the body. The orbitofrontal cortex appears to function as a site for integrating sensory information from the body and sensory information from the world to guide behavior. Closely related to core affect, the authors propose that anterior cingulate and dorsolateral prefrontal cortex play vital roles in attention, with anterior cingulate supporting the use of sensory information for directing attention and motor responses during response selection and with dorsolateral prefrontal cortex supporting executive attention. In many psychological construction approaches, emotions also involve the act of interpreting ones situation in the world relative to the internal state of the body, or what is referred to as conceptualization. In support of this idea, the dorsomedial prefrontal cortex and hippocampus were consistently active in this meta-analysis, regions that appear to play an important role conceptualizing during emotion, which are also involved in simulating previous experience (e.g. knowledge, memory). Language is also central to conceptualizing, and regions that support language, including ventrolateral prefrontal cortex, were also consistently active across studies of emotion experience and perception.[89]

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