[Continued from above] . . . Anatomy of the Stomach, Gallbladder, and Pancreas

Stomach A hollow muscular organ about the size of 2 closed fists, the stomach is located inferior to the diaphragm and lateral to the liver on the left side of the abdominal cavity. The stomach forms part of the gastrointestinal tract between the esophagus and the duodenum (the first section of the small intestine).

The wall of the stomach contains several layers of epithelium, smooth muscle, nerves, and blood vessels. The innermost layer of the stomach is made of epithelium containing many invaginations known as gastric pits. The cells of the gastric pits produce gastric juice - an acidic mixture of mucus, enzymes and hydrochloric acid.

The hollow portion of the stomach serves as the storage vessel for food before it moves on to the intestines to be further digested and absorbed. At the inferior end of the stomach is a band of smooth muscle called the pyloric sphincter. The pyloric sphincter opens and closes to regulate the flow of food into the duodenum.

Gallbladder The gallbladder is a 3-inch long pear-shaped sac located on the posterior border of the liver. Connected to the bile ducts of the liver through the cystic duct, the gallbladder receives bile transported from the liver for storage on a regular basis to prepare for the digestion of future meals. During digestion of a meal, smooth muscles in the walls of the gallbladder contract to push bile into the bile ducts that lead to the duodenum. Once in the duodenum, bile helps with the digestion of fats.

Pancreas The pancreas is a 6-inch long heterocrine gland located inferior to the stomach and surrounded by the duodenum on its medial end. This organ extends laterally from the duodenum toward the left side of the abdominal cavity, where it tapers to a point.

The pancreas is considered a heterocrine gland because it has both endocrine and exocrine gland functions. Small masses of endocrine cells known as pancreatic islets make up around 1% of the pancreas and produce the hormones insulin and glucagon to regulate glucose homeostasis in the blood stream. The other 99% of the pancreas contains exocrine cells that produce powerful enzymes that are excreted into the duodenum during digestion. These enzymes together with water and sodium bicarbonate secreted from the pancreas are known as pancreatic juice.

Digestion The stomach, gallbladder, and pancreas work together as a team to perform the majority of the digestion of food.

Storage The stomach, gallbladder, and pancreas all function together as storage organs of the digestive system. The stomach stores food that has been ingested and releases it in small masses to the duodenum. The release of small masses of food at a time improves the digestive efficiency of the intestines, liver, gallbladder, and pancreas and prevents undigested food from making its way into feces.

As they are accessory organs of the digestive system, the gallbladder and pancreas have no food passing through them. They do, however, act as storage organs by storing the chemicals necessary for the chemical digestion of foods. The gallbladder stores bile produced by the liver so that there is a sufficient supply of bile on hand to digest fats at any given time. The pancreas stores the pancreatic juice produced by its own exocrine glands so that it is prepared to digest foods at all times.

Secretion The stomach, gallbladder, and pancreas all share the common function of secretion of substances from exocrine glands. The stomach contains 3 different exocrine cells inside of its gastric pits: mucous cells, parietal cells, and chief cells.

The mixture of mucus, hydrochloric acid, and pepsin is known as gastric juice. Gastric juice mixes with food to produce chyme, which the stomach releases into the duodenum for further digestion.

The gallbladder stores and secretes bile into the duodenum to aid in the digestion of chyme. A mixture of water, bile salts, cholesterol, and bilirubin, bile emulsifies large masses of fats into smaller masses. These smaller masses have a higher ratio of surface area to volume when compared to large masses, making it easier for them to be digested.

The pancreas stores and secretes pancreatic juice into the duodenum to complete the chemical digestion of food that began in the mouth and stomach. Pancreatic juice contains a mixture of enzymes including amylases, proteases, lipases, and nucleases.

Hormones Several hormones are used to regulate the functions of the stomach, gallbladder, and pancreas. The hormones gastrin, cholecystokinin, and secretin are secreted by organs of the digestive system in response to the presence of food and change the function of the stomach, gallbladder, and pancreas. Our pancreas produces the hormones insulin and glucagon to affect the behavior of cells throughout the body.

Prepared by Tim Taylor, Anatomy and Physiology Instructor

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Stomach, Gallbladder and Pancreas | Interactive Anatomy Guide

WHAT'S THIS

Anatomy Arcade makes basic human anatomy come ALIVE through awesome free flash games, interactives and videos.

Anatomy Arcade is perfect for the novice teenager in the classroom, right through to students and professionals of health care looking for a fun way to revise.

With the help of Media Saints, we plan on making many more iPad apps. Poke-A-Muscle is next followed by a digestive game called Eat Me and eventually a very exciting, whole body system game called Machine Man!

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Anatomy Arcade

What is basic anatomy?

Basic anatomy is one of the three major subdivisions of human anatomy (with Gross Anatomy and Histology). It is actually a code to understand the terminology and concepts of anatomy. Basic anatomy introduces the students to the definitions, terminology and basic theme of anatomy. Without knowing the very basic concepts, it is very difficult to understand the complex structural details of human body and that is why, basic anatomy must be learned completely before learning human anatomy. In the gross anatomy, you will study the general and special features of Humerus (arm bone) however, you first need to know what is a bone and what are its characteristics. This part of anatomical study is covered in Basic Anatomy and from this illustration, you can easily imagine the importance of it.

MANanatomy.com explains basic anatomy in a taxonomic way. The complete description is made in 9 sections, which are all listed below. All the necessary details are explained, however we have tried to keep things as brief as possible because you should only be getting basic knowledge in basic anatomy. When you complete the course of Basic anatomy at MANanatomy.com, you will find yourself at significant benefit in the process of learning the complete anatomy of human body. The explanation of basic anatomy is divided into the following sections;

All the links above explain only the basic anatomy of various systems of human body. To learn the detailed gross anatomy, visit the links below;

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Basic Anatomy

Male and female 3D gross human anatomy models

Each model includes 4,600+ structures. All body systems covered: nervous (brain, nerves, sensory organs), skeletal (ligaments and bursae), circulatory, muscular, digestive, urinary, lymphatic, endocrine, and reproductive. Additional microanatomy models detail structures of sensory organs (skin, ear, eye, tongue).

Each body system includes a series of quick-to-get-to preset views that showcase key organs and surrounding anatomy. Use them to study, teach, or learn. Rotate around a 2D model of the heart. Dissect away arteries that supply blood to the cerebrum. Zoom in and study the ducts of the liver, gall bladder, and pancreas. Edit any view and save to view again.

Read detailed definitions, Latin names, and descriptions of injuries, diseases, and pathologies. Listen to pronunciations. Test your knowledge with over 1,000 quiz questions.

"It's a beautiful tool to work with. It helps me to explain certain problems of the human body to students and patients."

"It makes it so much easier for my patients to see and understand where and why they experience pain. Just a wonderful app!"

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Note: Check your device type for specifics and additional costs. Additional content includes pins and pain that detail muscle attachments, 3D rotatable models that show common muscle movements, bony landmarks, and patient education physiology and pathology animations. Watch a demo: An emergency room doctor explains gallstones.

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Human Anatomy Atlas by Visible Body

America's Funniest Home Videos

Actor and Dancing with the Stars Season 19 Champion, Alfonso Ribeiro, is named new host of ABCs Americas Funniest Home Videos, as announced by Tom Bergeron during the season finale of DWTS.

After receiving hundreds of inquiries, stacks of video submissions and a very close audition race, one smile, one funny and sincere delivery became our standout favorite -- Alfonso Ribeiro, said Vin Di Bona, executive producer. We look forward to Alfonso leading AFV into the next generation of family friendly viewership.

ABCs longest-running primetime entertainment show, Americas Funniest Home Videos, returns for season 26 this fall with the same mission -- giving families something genuinely funny to enjoy together on Sunday nights. Along with a new host, the upcoming season will welcome an abundant supply of fresh clips to keep families laughing from coast to coast.

In its 25 seasons to date, Americas Funniest Home Videoshas given away over $14 million in prize money and evaluated more than a million video clips from home viewers. AFV has become an iconic part of American pop culture, as evidenced by its entry into the Smithsonians permanent entertainment collection. Today, AFV is seen in 193 territories around the world, spreading American humor and clumsiness across the globe! Vin Di Bona is Executive Producer.

Viewers wishing to submit home videos to Americas Funniest Home Videosshould visit AFV.comfor details.

Following the home invasion murder of Matt Skokie a war vet and an assault on his wife Gwen, four suspects are brought into custody: Tony Gutirrez, an impressionable teen who got in way over his head even under the watchful eye of his dedicated and hard-working father, Alonzo Gutirrez. Hector Tontz, a young man who has lived life on the fringes of society and has made bad decisions just to survive. Carter Nix and Aubry Taylor, two incredibly lost souls whose addiction to drugs and to one another has become destructive and paralyzing.

Though the suspects fit a profile, they and their situations are far more complicated than anyone would have initially believed... As is true for the victims themselves. As RussSkokieand Barb Hanlon divorced and estranged arrive to both bury their son Matt, and seek a measure of justice for his killing, they discover their son may have been far from an innocent bystander in his own murder.

Told from the points of view of all those involved, this new drama examines preconceptions on faith, family, gender, race, class and other aspects of our social experience with an approach and perspectives historically underserved in media.

American Crimestars Felicity Huffman as Barb Hanlon, Timothy Hutton as Russ Skokie, W. Earl Brown as Tom Carlin, Richard Cabral as Hector Tontz, Caitlin Gerard as Aubry Taylor, Benito Martinez as Alonzo Gutirrez, Penelope Ann Miller as Eve Carlin, Elvis Nolasco as Carter Nix, Johnny Ortiz as Tony Gutirrez and guest starring Regina King as Aliyah Shadeed.

American Crimeis created and executive produced by Oscar winner John Ridley (12 Years a Slave). Michael J. McDonald also serves as executive producer. American Crime is produced by ABC Studios.

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Bachelor Nation was heartbroken when fan-favorite Ben Higgins, the charming software salesman, was sent home by Kaitlyn Bristowe onThe Bachelorette. Ben saw a great life with Kaitlyn, only to have it disappear before him when he was left without a rose. It wasnt easy for Ben to open himself up to love onThe Bachelorettebecause hes been hurt in past relationships. However, now knowing he is capable of being in love and being loved, he is ready to put the heartbreak behind him as he searches for his one true love when he stars in the milestone 20thseason of ABCs hit romance reality series,The Bachelor, returning to ABC in January 2016.

The long awaited second season of last summers #1 new unscripted hit series, Bachelor in Paradisereturns to ABC.The cast of contestants is comprised of former fan favorites and controversial characters from the Bachelorfranchise are back looking for a second chance at love.

They all left The Bacheloror The Bachelorettewith broken hearts, but now theyll travel to a romantic paradise hoping to turn a potential summer fling into the real thing. Over the course of the season, well follow cast members as they explore new relationships and viewers at home will watch as they fall in love or go through renewed heartbreak.

If last season was any indication, Bachelor in Paradisewill feature shocking twists, surprises, unexpected guests and some of the most unlikely relationships in Bachelorhistory. In true Bachelorfashion, its sure to be an amazing journey.

Hosted by Chris Harrison, Bachelor in Paradiseis produced by Next Entertainment in association with Warner Horizon Television. Mike Fleiss, Martin Hilton and Alycia Rossiter are executive producers.

Bachelor in Paradise: After Paradise a live one-hour weekly after-show, will debut onMONDAY, AUGUST 3at 9:00 p.m., ET/PT, immediately following the two-night premiere of Bachelor in Paradise. The second season of last summers #1 new unscripted series, Bachelor in Paradise, kicks off onSUNDAY, AUGUST 2(8:0010:00 p.m., ET/PT) andMONDAY, AUGUST 3(8:009:00 p.m., ET/PT).

New episodes of Bachelor in Paradisewill continue to air on Sundays (8:0010:00 p.m., ET/PT) and Mondays (8:009:00 p.m., ET/PT), with Bachelor in Paradise:After Paradiseairing afterward on Mondays (9:0010:00 p.m. ET/PT.) The after-show episodes are hosted by Chris Harrison and co-host Jenny Mollen, and produced by Embassy Row, the company behind Watch What Happens Live and the Emmy-nominated Talking Dead.

Bachelor in Paradise:After Paradisewill feature host Harrison and co-host Mollen discussing and dissecting the most recent episodes of Bachelor in Paradise,alongside cast members and celebrity fans. Bachelor fans know Mollen from her prolific live tweeting during past seasons of The Bachelorand The Bachelorette, while Harrison is the man who has seen it all as the host of The Bachelor franchise since the first rose ceremony took place over 13 years ago. Together theyll present questions and comments from viewers, debut deleted scenes, outtakes and exclusive extra content, all the while allowing members of #BachelorNation to finally have their say.

Bachelor in Paradise:After Paradiseis executive produced by Mike Fleiss for Next Entertainment in association with Warner Horizon Television and Michael Davies, Jen Patton and Elan Gale for Embassy Row.

ABCs hit romantic reality series, The Bachelorette, will kick off its 11th season continuing the surprises of this seasons Bachelor with the biggest one of all: there will be two Bachelorettes: the charming, charismatic beauty, Britt, who captivated Chris Soules and the rest of Bachelor Nation with a memorable hug on that first night at the Bachelor mansion, and Kaitlyn, the gorgeous, fun-loving, warm-hearted, but irreverent firecracker who let down her guard only to have her heart crushed. Who will the men prefer? Eventually, only one woman will be left to hand out the final rose. The Bachelorette returns to ABC, premiering MONDAY, MAY 18 (9:00-11:00 p.m., ET), on the ABC Television Network.

It was the hug felt around the world. And no one will ever forget it. When stunning Britt Nilsson pulled up at the Bachelor Mansion and approached Chris, she was trembling with nervous anticipation. Moments later, she found herself in an embrace that captured both Chris and the countrys heart. Later that night, Chris confirmed the intensity of that embrace when he handed Britt the coveted first impression rose. And with that, a love affair began to blossom.

As Chriss journey evolved, no onecertainly none of the other girlscould deny the connection between Britt and the handsome farmer. Their kisses were passionate, their conversations intimate. However, what seemed like true love all came to a screeching halt just before hometown dates. Britts dream of finding a husband was shattered. She left in tears, returning to her hometown in Michigan to mend her heart with her loving family by her side.

Born just outside Detroit, Michigan, Britt eventually moved to Los Angeles to attend college at Azusa Pacific University. After school, she stayed in California, moving to Hollywood to pursue a career in modeling. After giving up modeling, Britt worked as a waitress, spreading her infectious personality while serving others. She also began volunteering at a local church, where you can often find her greeting congregants at the door.

Since she left the show, America just cant stop talking about Britt and she is back and determined to find the elusive, true love she has been looking for her entire life. She knows that this process worked once for her, and she cant wait to give it another go.

And then there is Kaitlyn Bristowe. Millions watched in quiet astonishment when Chris explained to a heartbroken Kaitlyn that she was not the woman with whom he would be spending the rest of his life. Her eyes brimming with tears, she stepped inside a waiting car to head back to her single life.

Kaitlyn is truly one of a kind. Shes beautiful, irreverent, and undeniably hilarious. In the past, however, her playful demeanor has often kept her from opening up and being vulnerable to love. It was her experience on the Bachelor that helped her finally tap into that part of her heart that had been dormant for so long. Even though she went home without the love she was so desperately looking for, Kaitlyn is thankful for her time with Chris. And nowmore than evershe is ready to let down those walls and find love again.

The daughter of a ballerina, Kaitlyns love of dance took hold at a very young age, and she hasnt stopped moving since, neither figuratively nor literally. Currently, she teaches spin classes. However, Kaitlyns ready to trade in the cycling shoes and the gym for a pair of sparkly high heels and a house near the Bachelor mansion. Viewers were thankful for the laughs and smiles she gave them along the way, as her electric personality and indelible sense of humor lit up the screen each week. Kaitlyn was a huge fan favorite from the beginning, and remains so to this day. She is one hundred percent certain that this is the way she is going to find her husband, and wants everyone to share this once-in-a-lifetime ride with her.

ABC has picked upBattleBots, a reimagined take of the killer robot combat sport from Whalerock Industries and the creators of the originalBattleBotsfranchise, Ed Roski and Greg Munson. The homeade robots will battle against each other, in a single elimination tournament style format, until there is one champion. The six episode series is anticipated to air this summer. MGM Television, which has a development deal with Whalerock Industries, will be distributing the program internationally.

The new series promises to wow viewers with next generation robotsbigger, faster and stronger than ever before. The show will have a greater emphasis on the design and build elements of each robot, the bot builder backstories, their intense pursuit of the championship and the spectacle of the event. Separate weight classes will be eliminated so that robots of all sizes will battle against each other. State of the Art Onboard Technology and Cameras will provide audiences with enhanced viewing and combat analytics. There will be cash prizes for winners in the Championship Rounds.

Executive Producers are Lloyd Braun, Chris Cowan, Ed Roski and Greg Munson.

Beyond the Tank is a three-week event from the producers of the Emmy-winning reality series,Shark Tank. The one-hour episodes ofBeyond the Tank, from Sony Pictures Television and United Artists Media Group, will feature the captivating and surprising outcomes after the Sharks strike a deal with the entrepreneurs onShark Tank. As the Sharks travel across America to mentor the entrepreneurs, assess the businesses and provide their industry expertise -- to make a profit -- audiences will realize the challenges and intrepid negotiations are never over.Watch as the Sharks roll up their sleeves to help their entrepreneurs make the tough decisions that hopefully lead to success, growth and profits.

The Sharks are: billionaire Mark Cuban, owner and chairman of AXS TV and outspoken owner of the 2011 NBA championship Dallas Mavericks; real estate mogul Barbara Corcoran; Queen of QVC Lori Greiner; technology innovator Robert Herjavec; fashion and branding expert Daymond John; and venture capitalist Kevin OLeary.

Audiences familiar with the compelling ups and downs of the negotiations will be further engaged in the drama that takes place after the entrepreneurs appearance onShark Tank. What lies in the aftermath of their investment? Did a promising deal turn sour or launch a million dollar profit margin?

Beyond the Tank will feature The Sharks -- tough, self-made, multi-millionaire and billionaire tycoons -- taking a look back at pastShark Tank pitches and deals to examine the highs and lows that can come from an appearance in the tank. The series will revisit entrepreneurs whose businesses were groundbreaking in terms of their technology, business model or branding who have taken their business to new heights with the help of the Sharks; entrepreneurs and their Shark investors who gambled on their businesses and then lost; businesses that multiple Sharks fought hard against each other to secure, and more. We will learn more about the entrepreneurs personal journeys as well as their struggles and triumphs as they persevere to pursue the American dream.

Mark Burnett, Clay Newbill and Leslie Garvin are the executive producers ofBeyond the Tank. Mark Burnett, Clay Newbill and Phil Gurin are the executive producers ofShark Tank, which is based on the JapaneseDragons Den format created by Nippon Television Network Corporation. The series is produced by United Artists Media Group in association with Sony Pictures Television.

Andre 'Dre' Johnson (Anthony Anderson) has a great job, a beautiful wife, Rainbow (Tracee Ellis Ross), four kids and a colonial home in the 'burbs. But has success brought too much assimilation for this black family? With a little help from his dad (Laurence Fishburne), Dre sets out to establish a sense of cultural identity for his family that honors their past while embracing the future.

black-ish stars Anthony Anderson as Dre, Tracee Ellis Ross as Rainbow, Yara Shahidi as Zoey, Marcus Scribner as Andre Jr.,Miles Brownas Jack, Marsai Martin as Diane and Laurence Fishburne as Pops.

Billy and Cody Lefever dream of a new life beyond their working class roots and move to "The Bakken" in North Dakota, booming after the biggest oil discovery in American history. Theyre soon pitted against a ruthless tycoon who forces them to bet big and put everything on the line, including their marriage.

Starring Don Johnson as Hap, Chace Crawford as Billy, Rebecca Rittenhouse as Cody, Delroy Lindo as Tip, Amber Valletta as Carla, Scott Michael Foster as Wick, and India De Beaufort as Jules.

"Blood & Oil" is written by Josh Pate and Rodes Fishburne. Executive producers are Tony Krantz, Josh Pate, Rodes Fishburne, Drew Comins, and Don Johnson; produced by ABC Signature.

Viewers will ride along with the proud men and women of the Boston Emergency Services, one of Americas most seasoned team of first responders: the first step in the chain of trauma care. It was this same group that answered the desperate calls of runners and spectators two years ago when the bombs went off at the Boston Marathon. Treating the injured and ferrying the wounded to hospitals, the Boston EMS earned the gratitude of a shell-shocked and grief-stricken city with their cool-headed professionalism. In Boston EMSviewers will meet some of the heroes of that terrible day as they answer new calls and respond to a daily dose of trauma and mayhem.

When viewers first met Richard Castle, a famous mystery novelist, he was creatively blocked. But when the NYPD questioned him in connection with a series of murders staged to imitate crime scenes from his books, Castle found inspiration in NYPD DetectiveKate Beckett.Once that initial case was solved, Castle and Beckett continued to investigate strange homicides in New York, combining Castles writer intuition and Becketts creative detective work. In the Season 7 finale, Castle revealed some of his backstory for becoming a mystery writer, while Beckett was faced with a choice about her future will she choose to pursue a new challenge or stay where she is?

Though they instantly clashed, sparks of another sort began to fly, leading both to danger and a hint of romance as Castle stepped in to help find the copycat killer. Once that initial case was solved, Castle and Beckett continued to investigate strange homicides in New York, combining Castle's writer intuition and Beckett's creative detective work. Then, after four seasons of will they or wont they, Castle and Beckett finally gave into their feelings for each other. The fun and conflict continue to escalate as the crime-solving dynamic duo navigate a whole new chapter in their relationship.

Season 1: Mystery writer Richard Castle abandons his successful Derrick Storm book series. Hes found a new muse in Detective Kate Beckett. Shes the inspiration for his character, Nikki Heat. As he helps the police solve New Yorks toughest murder mysteries, Castle learns that Becketts mother was killed when she was younger. He cant help but look into the case. Castle discovers that Becketts mom was not the victim of a random act of violence. She was targeted. For detailed recaps please visit Castles Season 1 Episode Guide.

Season 2: Castle enjoys success with his Nikki Heat novel, but also feels the backlash of looking into the murder of Becketts mom. Highlights of the season include a North Pole murder, a scary Vampire Weekend, a dalliance with a dominatrix and Castles daughter, Alexis, scoring an internship at the precinct. Castle is flustered when his partner dates the handsome Detective Demming and Beckett isnt thrilled to see Castle getting chummy with his ex-wife. For detailed recaps please visit Castles Season 2 Episode Guide.

Season 3: Things kick off with a bang when Castle is arrested for murder. Spoiler Alert: He didnt do it. In ensuing cases, Beckett goes up against her former training officer. She and Castle also encounter a vicious murderer known as 3XK, or the Triple Killer. Hollywoods version of Nikki Heat shows up at the precinct. Theres a dirty bomb set to go off somewhere in New York and theres a trip to L.A. on the set of Naked Heat. Finally, Captain Montgomery is gunned down by killers who then set their sights on Beckett. For detailed recaps please visit Castles Season 3 Episode Guide.

Season 4: Beckett fights for her life after being shot by a sniper. She recovers only to keep secret that she heard Castle say he loves her. Captain Victoria Iron Gates takes over the squad and Detective Kevin Ryans gun is used in a murder. The case has ties to the elusive Triple Killer. Castle is held hostage during a bank robbery and the team is seen in 1947 for the case of The Blue Butterfly. Theres a CIA showdown with rogue agents and a woman from Castles past. Beckett gets dangerously close to the truth of her moms murder just before she and Castle finally give in to their passion. For detailed recaps please visit Castles Season 4 Episode Guide.

Season 5: Castle and Beckett try to keep their new relationship a secret as they learn the man responsible for Johanna Becketts murder is the powerful Senator Bracken. When Alexis is kidnapped, Castle gets his daughter back with help from a man hes never really methis father. Detective Ryan gets the good news that a baby is on the way and Castle receives the greatest birthday gift of his life thanks to Becketts Rear Window-esque surprise in the 100th episode. The mystery man and his muse hit a crossroads when Beckett gets an incredible job offer in DC. Wanting more out of their relationship, Castle gets down on one knee to ask his partner to marry him. The long wait to hear Becketts response came in the Season 6 premiere. For detailed recaps please visit Castles Season 5 Episode Guide.

Season 6: Beckett accepts Castles proposal of marriage as well as a job at the Justice Department in DC. The latter doesnt pan out, so she heads back to the Big Apple. Castle struggles with his daughters decision to move in with her flakey boyfriend, Pi. Alexis eventually finds her way back home. Ryan becomes proud dad and Castle briefly reconnects with his father. Beckett is finally able to take down the evil Senator Bracken. The man behind her mothers murder will finally pay for his crimes. After Beckett dissolves a marriage she didnt realize she was in, the path is clear for her to finally marry Castle. The groom is a no show though. Beckett fears the worst when Castles car is found engulfed in flames. For detailed recaps, please visit Castle's Season 6 Episode Guide.

Season 7: Castle is finally found after missing his wedding to Beckett and disappearing for two months. With no memory of the lost time, Castle is forced to return to his normal life without any answers. It's not until a mysterious recurring dream and a trail of bodies lead Castle to Jenkins, the man responsible for his disappearance. Jenkins tells Castle he helped save lives, but will he ever know the whole truth? And after teaming up with a mobster on a murder case gets Castle banned from working with the NYPD, he pursues a new line of work: Private Investigator. Meanwhile, Beckett finds herself at a professional crossroads when, after passing the Captains exam, she learns that she's also being vetted for political office. Which path will she choose? For detailed recaps, please visit Castle's Season 7 Episode Guide.

Executive producers are Terence Paul Winter, Alexi Hawley, Rob Bowman, Rob Hanning and Armyan Bernstein. Castle is produced by ABC Studios.

View ABC.com's favorite Caskett (Castle and Beckett) moments

The Chew celebrates and explores life through food, with a group of dynamic, engaging, fun, relatable co-hosts who serve up everything to do with food -- from cooking and home entertaining to food trends, restaurants, holidays and more -- all aimed at making life better, fuller and more fun. It is broadcast live, weekdays, from New York City.

The Chew stars Mario Batali, Michael Symon, Carla Hall, Clinton Kelly and Daphne Oz.

Mario Batali is co-owner of 17 restaurants across the country, including his flagship New York City restaurant Babbo. He has hosted a variety of television shows for Food Network, including Ciao America and Molto Mario. Batali is also the author of eight cookbooks, including the James Beard Award Winning, Molto Italiano: 327 Simple Italian Recipes.

Michael Symon is a star of the Food Network series Iron Chef America. Symon is the owner of five restaurants, including the critically-acclaimed Lola and Lolita, cornerstones of his hometowns dining scene in Cleveland, OH. In 1998, Symon was named Best New Chef by Food & Wine Magazine. He is known for his infectious laugh and is an avid tattoo enthusiast who has a Got Pork tattoo emblazoned on his chest. Symon enjoys spending time with his wife, Liz, and their two dogs, Ruby and Ozzy.

Carla Hall is best known as a competitor on Bravos Top Chef, where she won over audiences with her fun catch phrase "Hootie Hoo" and philosophy to always cook with love. She is the owner of Alchemy by Carla Hall, an artisan cookie company that specializes in creating sweet and savory "petite bites of love." Hall is a true believer that, "If youre not in a good mood, the only thing you should make is a reservation."

Clinton Kelly is a familiar face to fashionistas around the country as style host of the TLC series What Not to Wear. He has also appeared in several specials for TLC, including: The Miss America Pageant; Fashioning a Home with Clinton Kelly; and Mind Your Manners and Redo My Spouse. Kelly is also the author of Freakin Fabulous: How to Dress, Speak, Behave, Eat, Drink, Entertain, Decorate and Generally Be Better Than Everyone Else and Oh No She Didnt: The Top 100 Style Mistakes Women Make and How to Avoid Them. In December 2010, Kelly launched the style app Stylerx for the iPhone and web.

Daphne Oz is The Chew's fresh face of healthy living and resident practical tipster. In 2006, she wrote her national bestseller The Dorm Room Diet, sharing the healthy lifestyle plan she developed at school that helped her permanently shed thirty pounds. Oz also helped to found HealthCorps, a non-profit organization that equips teenagers with educational information in the areas of nutrition, exercise and stress management. She is a newlywed who will celebrate her first wedding anniversary later this month.

Produced by Gordon Elliott's Chew Productions for the ABC Television Network, The Chew is an innovative and groundbreaking new lifestyle series.

Get ready for a brand new season of salsas, sambas and spray-tans as Dancing with the Stars returns MONDAY, SEPTEMBER 14 8|7c with an all-new cast vying for the coveted Mirrorball Trophy!

Tom Bergeron and Erin Andrews will be back to guide us through this exciting new season along with your favorite judges. Of course, its still all about the fans who ultimately help determine which teams make the cut each week with their votes during the biggest dance party on the planet!

The stars, the drama, the glamour and the glitter are back on ABC! Dancing with the Stars returns on MONDAY, SEPTEMBER 14 8|7c with a sensational two-hour season premiere. On TUESDAY, SEPTEMBER 22 9|8c, brace yourself for the first elimination of the season with the Dancing with the Stars: Results Show.

Doctor turned actor/comedianKen Jeong(Community, The Hangover), plays Dr. Ken, a brilliant physician with no bedside manner. He is always trying to be a good doctor, as well as a good husband and dad to his two kids. However, these good intentions have a way of driving everyone crazy at both work and at home. Luckily, his therapist wife Allison is just the right partner to keep things sane.

Dr. Kenstars Ken Jeong as Dr. Ken, Suzy Nakamura as Allison, Tisha Campbell-Martin as Damona, Dave Foley as Pat, Jonathan Slavin as Clark, Albert Tsai as Dave and Krista Marie Yu as Molly. ABC's new comedyDr. Kenwas written by Jared Stern, Ken Jeong, and Mike OConnell. Executive Producers are Jared Stern, Ken Jeong, John Davis, John Fox and Mike Sikowitz, with Mike OConnell as co-executive producer.Dr. Kenis produced by Sony Pictures Television and ABC Studios.

Its the '90s and 12 year old, hip-hop loving Eddie (Hudson Yang) just moved to suburban Orlando from DCs Chinatown with his parents (Randall Park and Constance Wu). Its culture shock for his immigrant family in this comedy about pursuing the American Dream.Fresh Off the Boatis based on Chef Eddie Huang's memoirFresh Off the Boat.

Fresh Off the Boatstars Randall Park as Louis, Constance Wu as Jessica, Hudson Yang as Eddie, Forrest Wheeler as Emery and Ian Chen as Evan.

Fresh Off the Boatis executive produced and written by Nahnatchka Khan and executive produced by Jake Kasdan for 20th Century Fox Television.

Screenwriter/executive producer Dan Fogelman (Crazy, Stupid, Love; Tangled; Cars) reunites with Broadway and Hollywood award-winning musical team composer Alan Menken (The Little Mermaid, Aladdin, Beauty and the Beast) and lyricist Glenn Slater (The Little Mermaid, Tangled) for the return of last seasons breakout musical comedy extravaganza,Galavant. Having discovered the dark side of Madalena, our dashing heros adventures continue as he embarks on an unlikely bromance with King Richard and fights to rekindle the romance with his true love Isabella.

Galavantstars Joshua Sasse as Galavant, Timothy Omundson as King Richard, Vinnie Jones as Gareth, Mallory Jansen as Madalena, Karen David as Isabella and Luke Youngblood as Sid.

Dan Fogelman, Alan Menken, Glenn Slater, Chris Koch, Kat Likkel and John Hoberg serve as executive producers. Abbey C Studios Ltd. Produces Galavant for ABC Studios.

General Hospital, which celebrated its golden anniversary on April 1, 2013, continues its tradition of passion, intrigue and adventure that takes place in the fictional town of Port Charles in upstate New York. The glamour and excitement of those who have come to find their destinies in this familiar seaport town intertwine with the lives, loves and fortunes of beloved, well-known faces. As always, love, danger and mind blowing plot twists continue to abound on General Hospitalwith contemporary storylines and unforgettable characters.

At 50-plus historic years and growing, General Hospitalhas received the prestigious Emmy Award for Outstanding Daytime Drama a record eleven times. The medical drama is the longest running American soap opera currently in production and the longest running scripted drama on television currently in production. Filmed in Hollywood, CA, the show will air its 13,000th episode on February 24, 2014.

The producing and writing teams of General Hospitalconsistently deliver thrilling and action-packed storylines featuring romantic moments, lost loves rekindled, dysfunctional family dynamics, suspenseful weddings, twisted villains, adventurous heroes and so much more. As a result, the shows ratings have rocketed this season, making General Hospitalthe #1 daytime network program with women 18-49. Furthermore, GH posts the biggest yearly gains out of all the daytime network dramas with women 25-54.

The show that TV Guide hailed as the "All-Time Best Daytime Soap" in their 40th Anniversary special edition, General Hospitalhas also won a number of awards from the Directors Guild and the Writers Guild for Outstanding Achievement. General Hospitalis known for its high profile celebrity guest stars and some of the more iconic names include Milton Berle, Sammy Davis, Jr., and Elizabeth Taylor.

For many years, General Hospitalhas worked alongside and been praised by numerous national organizations for elevating public awareness of important health and social issues. Some of those real-life issues featured in conjunction with specific storylines include awareness of sexual responsibility, HIV/AIDS-related storylines, tolerance and understanding for gay, lesbian and transgender people, bipolar disorder, accurate portrayals of tobacco, drug and alcohol addiction, breast cancer awareness, sexual child abuse and organ donation.

Several past and current cast members have received stars on the Hollywood Walk of Fame for their work on the show. Notably, in 1993, both the late Anna Lee (Lila Quartermaine) and original cast member John Beradino (Dr. Steve Hardy) received their stars on the Hollywood Walk of Fame.

General Hospitalwas created by husband-and-wife soap writers Frank and Doris Hursley and premiered on April 1, 1963. In 1978, Gloria Monty was brought in as executive producer and is credited with the creation of the first supercouple, characters Luke Spencer and Laura Webber. Their 1981 wedding brought in 30 million viewers and remains the highest-rated hour in American soap opera history.

The executive producer of General Hospital is Frank Valentini, and Ron Carlivati is the head writer. General Hospitalairs weekdays at 2e|1c|pon the ABC Television Network.

Frank Valentini, Executive Producer

Frank Valentini became executive producer of ABC'sGeneral Hospital in January 2012. Previously, he was executive producer of ABC's multi-award winning daytime drama, One Life to Live. Valentini was honored with an Emmy Award for producing in 2002 and two consecutive wins in 2008 and 2009 as a part of the One Life to Livedirecting team, and in 2011 for the ABC daytime What If webisodes. In addition, he was nominated for a DGA Award in 2002.

Prior to being named executive producer at One Life to Live, Valentini held various positions on the show, including associate director, stage manager and coordinating producer. In addition to his duties at OLTL, he served as a guest director on the ABC Daytime drama All My Children. In 2008, he added commercial director to his credits with the Endless Drama broadcast and web campaign for ESPN. He directed ABC Daytime's innovative series of What If webisodes that began airing on abc.com and soapnet.com on July 12, 2010. The 10-part series features well known characters from All My Children,One Life to Live and General Hospitalanswering the questions, What would happen if two characters from different soaps ran into each other? What would they say?

Valentini has a vast knowledge of contemporary music, which he acquired when he served as a radio station music director, talent scout for Steam Records and freelance writer for VH-1. He served for two years on the board of the New Group Theater Company. He received his degree in film & television production from the University of Buffalo. He has traveled to over 75 countries, and in 2002 he became a published photographer.

Before there were parenting blogs, trophies for showing up and peanut allergies, there was a simpler time called the 80s. For geekyand movie obsessedyoungest child Adam (Sean Giambrone), these were hiswonder years, and he faced them armed with a video camera to capture all the crazy. The Goldbergs are a loving family like any other -- just with a lot more yelling. Mom Beverly (Wendi McClendon-Covey) is a classic "smother," an overbearing, overprotective matriarch wholoves her delicious kids, but stillrules this brood with 100% authority and zero sense of boundaries. Dad Murray (Jeff Garlin) is gruff and sometimes oblivious, parenting with half his attention span but all his heart. Sister Erica (Hayley Orrantia) is popular and terrifying, doing her best to cover up that she's the smartest of the clan.Barry (Troy Gentile) isa passionate dreamer, who maybe dreams a little too big and who always gets the short end of the stick. Adam(Sean Giambrone)is the youngest, a camera-wielding future director whos navigating first love, and growing up with his family. Rounding out the family is beloved grandfather Al "Pops" Solomon (George Segal), the wild man of the clan, a shameless Don Juan whos learning as much from his family as he teaches them.

The Goldbergsstars Wendi McLendon-Covey (Bridesmaids) as Beverly Goldberg, Patton Oswalt (Ratatouille) as adult Adam Goldberg, Sean Giambrone as Adam Goldberg, Troy Gentile (Good Luck Chuck) as Barry Goldberg, Hayley Orrantia (The X Factor) as Erica Goldberg, with George Segal (Just Shoot Me) as Pops Solomon and Jeff Garlin (Curb Your Enthusiasm) as Murray Goldberg.

The Goldbergsis written and executive-produced by Adam F. Goldberg (Breaking In,Fanboys)and also executive-produced by Doug Robinson, Seth Gordon, Alex Barnow and Marc Firek.The Goldbergsis from Adam Sandlers production company, HappyMadison, and is produced by Sony Pictures Television. It is broadcast in720 Progressive (720P), ABCs selected HDTV format with a 5.1 channel surround sound.

Grey's Anatomy is the recipient of the 2007 Golden Globe Award for Best Television Series - Drama, and multiple Emmy nominations, including two for Outstanding Drama Series.

The doctors ofGrey Sloan Memorial Hospital deal with life-or-death consequences on a daily basis-it's in one another that they find comfort, friendship and, at times, more than friendship. Together they're discovering that neither medicine nor relationships can be defined in black and white. Real life only comes in shades of grey.

Season 1: Just before Meredith Grey begins her surgical residency at Seattle Grace, she has a one night stand with her new boss, Dr. Derek Shepherd. Just call this brilliant neurosurgeon "McDreamy." Mer's future "person," Cristina Yang, strikes up a relationship with cardiothoracic ace Preston Burke. Other interns include ex-model Izzie Stevens and her insecure BFF George O'Malley, who is branded "007" by the obnoxious Alex Karev because he has a license to kill. Dr. Miranda Bailey keeps the interns in line while Chief Richard Webber keeps the hospital running. For detailed recaps please visit Grey's Anatomy's Season 1 Episode Guide.

Season 2: Derek's wife, Addison, makes things awkward for Meredith, who must come clean that her mom is the brilliant surgeon/Alzheimer's victim, Ellis Grey. Izzie hooks up with Alex before falling for heart transplant patient Denny Duquette. George engages in a disastrous pairing with Meredith, who later hooks up with a hot veterinarian named Finn. Burke is shot. Surgery leaves him with tremors in his hand. Izzie cuts Denny's LVAD wire to move him up on the heart transplant list, but he dies in her arms. Izzie quits the program and Meredith must choose between Derek and Finn. For detailed recaps please visit Grey's Anatomy's Season 2 Episode Guide.

Season 3: Dr. Mark Sloan makes things McSteamy at Seattle Grace. Orthopedic surgeon Callie Torres strikes up a relationship with George. Cristina covers for Burke, who hides his hand tremors. There's a race to win the Chief's job once Richard announces retirement plans. Burke leaves Cristina on their wedding day. George loses his dad, proposes to Callie and hooks up with Izzie. Meredith has a near-death experience and must deal with the actual death of her estranged dad's new wife. Derek tells Meredith she's the love of his life and she, in turn, lets him know that it's over. So over. For detailed recaps please visit Grey's Anatomy's Season 3 Episode Guide.

Season 4: George repeats his intern year. Joining him is Little Grey, as in Meredith's half-sister, Lexie. The "really old guy" comes out of his coma. George and Izzie have bad sex. Cristina butts heads with new cardio doc Erica Hahn, who becomes intimate with Callie. Derek and Meredith have an uphill climb with their clinical trial, but they eventually "save a life." The two of them meet at Derek's patch of land. Meredith sets up a dazzling array of candles outlining where their house will be. For detailed recaps please visit Grey's Anatomy's Season 4 Episode Guide.

Season 5: Dr. Owen Hunt is a military doc who catches Cristina's eye. He becomes the hospital's head trauma surgeon. Dr. Arizona Robbins also arrives as the new pediatric surgeon. Mark and Lexie are a couple. Derek must overcome his shaken confidence to operate on Izzie, who has a brain tumor. He also preps for his wedding with Meredith via blue Post-It. In the season finale, a mangled man is brought in to the hospital after jumping in front of a bus to save a woman. He writes "007" on Meredith's hand. She knows instantly that this dying hero is George. For detailed recaps please visit Grey's Anatomy's Season 5 Episode Guide.

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Anatomy,a field in the biological sciences concerned with the identification and description of the body structures of living things. Gross anatomy involves the study of major body structures by dissection and observation and in its narrowest sense is concerned only with the human body. Gross anatomy customarily refers to the study of those body structures large enough to be examined without the help of magnifying devices, while microscopic anatomy is concerned with the study of structural units small enough to be seen only with a light microscope. Dissection is basic to all anatomical research. The earliest record of its use was made by the Greeks, and Theophrastus called dissection anatomy, from ana temnein, meaning to cut up.

Comparative anatomy, the other major subdivision of the field, compares similar body structures in different species of animals in order to understand the adaptive changes they have undergone in the course of evolution.

face: superficial arteries and veins in humansEncyclopdia Britannica, Inc.This ancient discipline reached its culmination between 1500 and 1850, by which time its subject matter was firmly established. None of the worlds oldest civilizations dissected a human body, which most people regarded with superstitious awe and associated with the spirit of the departed soul. Beliefs in life after death and a disquieting uncertainty concerning the possibility of bodily resurrection further inhibited systematic study. Nevertheless, knowledge of the body was acquired by treating wounds, aiding in childbirth, and setting broken limbs. The field remained speculative rather than descriptive, though, until the achievements of the Alexandrian medical school and its foremost figure, the Greek Herophilus (flourished 300 bce), who dissected human cadavers and thus gave anatomy a considerable factual basis for the first time. Herophilus made many important discoveries and was followed by his younger contemporary Erasistratus, who is sometimes regarded as the founder of physiology. In the 2nd century ce the Greek physician Galen assembled and arranged all the discoveries of the Greek anatomists, including with them his own concepts of physiology and his discoveries in experimental medicine. The many books Galen wrote became the unquestioned authority for anatomy and medicine in Europe because they were the only ancient Greek anatomical texts that survived the Dark Ages in the form of Arabic (and then Latin) translations.

Owing to church prohibitions against dissection, European medicine in the Middle Ages relied upon Galens mixture of fact and fancy rather than on direct observation for its anatomical knowledge, though some dissections were authorized for teaching purposes. In the early 16th century, the artist Leonardo da Vinci undertook his own dissections, and his beautiful and accurate anatomical drawings cleared the way for the Flemish physician Andreas Vesalius to restore the science of anatomy with his monumental De humani corporis fabrica libri septem (1543; The Seven Books on the Structure of the Human Body), which was the first comprehensive and illustrated textbook of anatomy. As a professor at the University of Padua, Vesalius encouraged younger scientists to accept traditional anatomy only after verifying it themselves, and this more critical and questioning attitude broke Galens authority and placed anatomy on a firm foundation of observed fact and demonstration.

From Vesaliuss exact descriptions of the skeleton, muscles, blood vessels, nervous system, and digestive tract, his successors in Padua progressed to studies of the digestive glands and the urinary and reproductive systems. Hieronymus Fabricius, Gabriello Fallopius, and Bartolomeo Eustachio were among the most important Italian anatomists, and their detailed studies led to fundamental progress in the related field of physiology. William Harveys discovery of the circulation of the blood, for instance, was based partly on Fabriciuss detailed descriptions of the venous valves.

The new application of magnifying glasses and compound microscopes to biological studies in the second half of the 17th century was the most important factor in the subsequent development of anatomical research. Primitive early microscopes enabled Marcello Malpighi to discover the system of tiny capillaries connecting the arterial and venous networks, Robert Hooke to first observe the small compartments in plants that he called cells, and Antonie van Leeuwenhoek to observe muscle fibres and spermatozoa. Thenceforth attention gradually shifted from the identification and understanding of bodily structures visible to the naked eye to those of microscopic size.

The use of the microscope in discovering minute, previously unknown features was pursued on a more systematic basis in the 18th century, but progress tended to be slow until technical improvements in the compound microscope itself, beginning in the 1830s with the gradual development of achromatic lenses, greatly increased that instruments resolving power. These technical advances enabled Matthias Jakob Schleiden and Theodor Schwann to recognize in 183839 that the cell is the fundamental unit of organization in all living things. The need for thinner, more transparent tissue specimens for study under the light microscope stimulated the development of improved methods of dissection, notably machines called microtomes that can slice specimens into extremely thin sections. In order to better distinguish the detail in these sections, synthetic dyes were used to stain tissues with different colours. Thin sections and staining had become standard tools for microscopic anatomists by the late 19th century. The field of cytology, which is the study of cells, and that of histology, which is the study of tissue organization from the cellular level up, both arose in the 19th century with the data and techniques of microscopic anatomy as their basis.

In the 20th century anatomists tended to scrutinize tinier and tinier units of structure as new technologies enabled them to discern details far beyond the limits of resolution of light microscopes. These advances were made possible by the electron microscope, which stimulated an enormous amount of research on subcellular structures beginning in the 1950s and became the prime tool of anatomical research. About the same time, the use of X-ray diffraction for studying the structures of many types of molecules present in living things gave rise to the new subspecialty of molecular anatomy.

Scientific names for the parts and structures of the human body are usually in Latin; for example, the name musculus biceps brachii denotes the biceps muscle of the upper arm. Some such names were bequeathed to Europe by ancient Greek and Roman writers, and many more were coined by European anatomists from the 16th century on. Expanding medical knowledge meant the discovery of many bodily structures and tissues, but there was no uniformity of nomenclature, and thousands of new names were added as medical writers followed their own fancies, usually expressing them in a Latin form.

By the end of the 19th century the confusion caused by the enormous number of names had become intolerable. Medical dictionaries sometimes listed as many as 20 synonyms for one name, and more than 50,000 names were in use throughout Europe. In 1887 the German Anatomical Society undertook the task of standardizing the nomenclature, and, with the help of other national anatomical societies, a complete list of anatomical terms and names was approved in 1895 that reduced the 50,000 names to 5,528. This list, the Basle Nomina Anatomica, had to be subsequently expanded, and in 1955 the Sixth International Anatomical Congress at Paris approved a major revision of it known as the Paris Nomina Anatomica.

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[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.

Prepared by Tim Taylor, Anatomy and Physiology Instructor

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Muscular System - Muscles of the Human Body

The doctors of Grey Sloan Memorial Hospital deal with life-or-death consequences on a daily basis -- it's in one another that they find comfort, friendship and, at times, more than friendship. Together they're discovering that neither medicine nor relationships can be defined in black and white. Real life only comes in shades of grey.

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Gray, Henry. 1918. Anatomy of the Human Body