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Page created: April 26, 2001. Text
revised: July 31, 2002.
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| Quick Overview of Key Ideas | |||
| What is a muscle? (Four descriptions presented): | |||
| Description A | Description B | Description C | Description D |
| Web Sites on Muscle Structure and Function. | |||
| Muscle Terminology and Classification of Movements of Skeletal Muscle. | |||
| A Synopsis of the Major Muscles in the Body. | |||
| Web sites showing the muscles in the body. | |||
| Recent Literature of Interest. | |||
| Sources of Information. | |||
| Go back to the Main overview page. | |||
Muscle is one of the more complex structures in the body and many of the details of muscle function remain obscure.
Parts of a Muscle Fibre
-(note: the terms muscle fibre and muscle cell are used interchangeably)
-outer membrane (in muscle, called sarcolemma)
-contain many cell nuclei (each contain DNA)
-contain many mitochondrion (pl. = mitochondria) (in muscle, they are called sarcosomes)
-contain a large endoplasmic reticulum (in muscle, called a sarcoplasmic reticulum)
-contain thousands of inner strands called myofibrils (they make up the cytoplasm [in muscle, called sarcoplasm] of the cell).
-myofibrils contain units called sarcomeres
-sarcomeres link up end to end to form one myofibril
sarcomeres contain actin thin filaments and myosin thick filaments: together responsible for muscle contraction
-actin (thin filaments) and myosin (thick filaments) interact in the sliding-filament model (our current theory of muscle function).
-myosin heads briefly bind to actin to cause the contraction
-muscle is made up out of proteins (the meat we eat is animal muscle): myosin, actin, tropomyosin and troponin make up 75% of muscle. About 24 other proteins make up the rest of the protein found in muscle.
-some neuromuscular diseases involve problems with one of these proteins
-the number of muscle fibers a person has appears to be a genetic factor and is fixed at birth, but new myofibrils inside the fibers are created by exercise
Muscle Function
-motor nerve cells (motor neurons) in the CNS carry signals from the brain down the spinal cord and out to muscles
-some neuromuscular diseases involve problems with the motor neurons
-one motor neuron connects to a group of muscle fibers to make up one motor unit
-where the nerve contacts the muscle is a bridge called the neuromuscular junction
-the neuromuscular junction is a synapse: no direct connection between the nerve and muscle: signals are sent across a tiny gap by a neurotransmitter called acetylcholine (Ach)
-when an impulse reaches the junction, Ach is released, crosses the gap and contacts the muscle fiber. When enough Ach accumulates, the muscle fiber fires (muscle contracts).
-some neuromuscular diseases involve problems with this neurotransmitter connection
Muscle Energy
-Muscle energy is supplied by a complex series of biochemical reactions depending
upon the demands placed upon the muscle. There are three subsystems that all
use chemical molecules called adenosine triphosphate (ATP).
-1). the immediate source of energy for muscle contraction is created when myosin uses (chemically breaks down) ATP. A muscle fiber contains only enough ATP to power a few twitches (up to about 10 seconds worth of energy). (like a runner doing a 100 meter sprint).
-2). skeletal muscle fibers contain about 1% glycogen. The muscle fiber can degrade this glycogen by a chemical process (glycolysis). Glycolysis yields two molecules of ATP for each pair of lactic acid molecules produced. This process does not need oxygen and can function for up to about 90 seconds (like a swimmer doing a 400 meter race)
-3). for longer periods of exertion (like a marathon race), oxygen is needed. In this third process, called aerobic respiration, oxygen is supplied by the blood to the muscle. When oxygen is present, glucose can be completely broken down into carbon dioxide and water in a process called aerobic respiration. The glucose can come from three different places:
=remaining glycogen supplies in the muscles
=breakdown of the liver's glycogen into glucose, which gets to working muscle through the bloodstream
=absorption of glucose from food in the intestine, which gets to working muscle through the bloodstream
-aerobic respiration is required to meet the ATP needs of a muscle engaged in prolonged activity (thus causing more rapid and deeper breathing), and is also required afterwards to enable the body to resynthesize glycogen (deep breathing continues for a time after exercise is stopped).
Muscle Exercise
-when muscle works, the current theory is that there is mechanical damage and micro-tears occur in the muscle fibers
-satellite cells (each with one nucleus) are scattered along the outside of the muscle fiber
-muscle work creates micro-tears or tiny rips in the fibres, damage stimulates a growth factor and attracts satellite cells
-satellite cells incorporate themselves into the muscle fiber
-the satellite cells produce protein and give their nuclei to the muscle fiber
-over time, the muscle fiber collects more nuclei and, in addition, the fibre expands
-exercise adds to muscle mass by adding more myofibrils (no new muscle fibres are created)
-in addition to exercise, there is a normal balance between protein synthesis and protein breakdown in the muscle.
-muscle composition involves a complex control mechanism that depends upon a number of factors including, activity level, diet and internal biochemical regulation
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Because muscles and nerves function together, this introduction begins with a basic overview of the nervous system.
See an overview. Click Here.
Taken from: http://brain.web-us.com/brain/aboutthebrain.htm
A picture of a neuron. Click Here.
Taken from: http://www.ccs.neu.edu/groups/honors-program/freshsem/19951996/cloder/neuron.html
Another good picture of a neuron. Click Here.
Taken from: http://www.mhhe.com/socscience/intro/ibank/ibank/0002.jpg
Another good picture of a neuron. Click Here.
From: http://www.mult-sclerosis.org/axon.html
Portions of the above from: http://www.subtlebraininjury.com/neuron.html
Sensory (Afferent) neurons: receive information from receptors and carries it back into the central nervous system (CNS) (spinal cord and the brain). [Receptors are special cells in the outer parts of the body (e.g. in the skin) that sense the environment and send their information back to sensory neurons].
Interneurons (associative): a sort of internal communication or bridge system, they act on signals from sensory neurons or other interneurons and link sensory and motor neurons.
Motor neurons (Efferent neurons): Motor neurons are nerve cells located in the brain, brainstem, and spinal cord. These motor neurons serve as connections from the central nervous system to the muscles in the body. They transmit information (signals) from the CNS back out to muscles and glands in the body.
Different types of neurons are affected in different types of disease. For example, motor neuron disease, also known as amyotrophic lateral sclerosis (ALS) or Lou Gehrig's disease, is a progressive disease that attacks motor neurons, components of the nervous system that connect the brain with the skeletal muscles. In ALS, the motor neurons deteriorate and eventually die, and though a person's brain is fully functioning and alert, the command to move never reaches the muscle.
Multiple Sclerosis (MS) is a disease where the myelin sheaths of the CNS white matter become damaged (demyelination) leading to reduced efficacy of nerve transmission along the axons.
Picture of a synapse. Click Here.
Taken from: http://www.zoobotanica.u-net.com/portfolio%20medicine%20pages/synapse.htm
Another neat picture of a synapse. Click Here.
Taken from: http://www.mhhe.com/socscience/intro/ibank/ibank/0003.jpg
Picture of a neuromuscular junction. Click Here.
Taken from: http://shs.westport.k12.ct.us/mjvl/anatomy/muscular/nmj_overview.GIF
Steps in muscle firing Click Here.
Taken from: http://shs.westport.k12.ct.us/mjvl/anatomy/muscular/stimulation.GIF
-Ligaments:
--Connect bone to bone. Have a skeletal stabilizing function.
--Made of white non-elastic, fibrous tissue
--Extremely strong
-Tendons:
--Connects muscle to bone
--Acts as a shock absorber and a connecting tissue
--Made of a combination of white fibrous and red elastic tissue
-Muscle:
--Contractile tissue
--Connected to tendons
--Elastic structure - absorbs shock in movement
--45% of total body weight is muscle
Muscles consist of long, slender cells (fibres) each of which is a bundle of finer fibrils. Within each fibril are relatively thick filaments of the protein myosin and thin ones of the protein actin as well as other proteins. When a muscle fibre shortens, the filaments remain essentially constant in length but slide past each other. Tension in active muscles is produced by the formation of cross bridges -- projections from the thick filaments that attach to the thin ones and exert forces on them. As the active muscle changes in length, the filaments slide past each other and the cross bridges repeatedly detach and reattach in new positions. Their action is similar to the way an extendable ladder moves when it is closed or in the action of pulling a rope in hand over hand. Some muscle fibres are several centimetres long, but most other cells are only a fraction of a millimetre long.
Muscle fibres appear to lie on a continuum that extends between slow contracting, slow fatiguing fibres at one extreme and fast contracting, fast fatiguing fibres at the other. Most classification schemes refer to the these extremes as Type I red, slow twitch (ST) fibres and Type II white, fast twitch (FT) fibres, where the difference in colour is due to the fact that red fibres have a higher content of myoglobin. Within an individual there are different proportions of the fibre types found in different muscles. Each individual has a genetically predetermined ratio of fast twitch to slow twitch fibres. In general, most people have a similar ratio of each of these fibres in their muscles. When an athlete displays extreme ability in an area of physical capability, the athlete will have an unusual ratio of fast and slow twitch muscle fibres. All muscle contains a mixture of slow and fast twitch fibres.
Speed of Contraction - slow twitch fibres contract at a slower rate compared with fast twitch fibres.
Muscle Fibre Force - Fast twitch fibres produce high power for a short period of time. These fibres are found in high concentrations in bodybuilders and power-lifters. Fast twitch fibres are slow to recover from exertion.
Muscle Endurance - Slow twitch fibres are capable of resisting fatigue whereas fast twitch fibres are easily fatigued. Slow twitch fibres are endurance fibres. They can produce low power for extended periods of time. Marathon runners are full of slow twitch fibres. This is why they do not look like bodybuilders.
Many muscles must work together to perform even the simplest jobs. These movements are coordinated by the nervous system, both through unconscious and conscious actions. Individual "units" of muscle fibres obey the "all or none" principle, meaning that all contract or none contracts.
Picture of a muscle cell. Click Here.
Taken from: http://bio.bio.rpi.edu/Parsons/Universal%20Files/Lectures/Lect1Musc/Lect1c.html
Another illustration of a muscle Click Here.
ATP is used to provide energy for body heat, nerve electricity, and muscle movement. An ATP molecule is held together by strong electrical forces which are set free when the molecule is broken apart in a chemical reaction inside the muscle. Through a complex process (only partly understood), these forces are converted into the kind of mechanical energy that will move our muscles. Suppose a muscle cell needs ten calories of energy to set off a muscle contraction. A unit of ATP is alerted to act by an agent, called a coenzyme, which splits off one phosphate unit and then delivers the required ten calories. In the process, the ATP is reduced to ADP (adenosine diphosphate). If the energy set free by the splitting off of phosphate units is not used for muscle contraction, it can be transferred to the other compounds in the muscle such as creatine and glucose. In so doing, the glucose is taken from a glycogen storage depot and begins to be broken down. The energy flowing from the crumbling glucose is used to furnish heat, convert some of the broken-down glucose back to glucose, and attach the liberated phosphate units to ADP to reform ATP. When this cycle is completed, the ATP units are ready for any new emergency.
Last paragraph from:http://www.nadh.com/refernce/ATPact20.htm#Top
Here is a more detailed description of muscle energy:
Your Body's Response to Exercise
Any type of exercise uses your muscles. Running, swimming, weightlifting -- any sport you can imagine -- uses different muscle groups to generate motion. In running and swimming, your muscles are working to accelerate your body and keep it moving. In weightlifting, your muscles are working to move a weight. Exercise means muscle activity!
As you use your muscles, they begin to make demands on the rest of the body. In strenuous exercise, just about every system in your body either focuses its efforts on helping the muscles do their work, or it shuts down. For example, your heart beats faster during strenuous exercise so that it can pump more blood to the muscles, and your stomach shuts down during strenuous exercise so that it does not waste energy that the muscles can use.
When you exercise, your muscles act something like electric motors. Your muscles take in a source of energy and they use it to generate force. An electric motor uses electricity to supply its energy. Your muscles are biochemical motors, and they use a chemical called adenosine triphosphate (ATP) for their energy source. During the process of "burning" ATP, your muscles need three things:
-They need oxygen, because chemical reactions require ATP and oxygen is consumed to produce ATP.
-They need to eliminate metabolic wastes (carbon dioxide, lactic acid) that the chemical reactions generate.
-They need to get rid of heat. Just like an electric motor, a working muscle generates heat that it needs to get rid of.
In order to continue exercising, your muscles must continuously make ATP. To make this happen, your body must supply oxygen to the muscles and eliminate the waste products and heat. The more strenuous the exercise, the greater the demands of working muscle. If these needs are not met, then exercise will cease -- that is, you become exhausted and you won't be able to keep going.
To meet the needs of working muscle, the body has an orchestrated response involving the heart, blood vessels, nervous system, lungs, liver and skin. It really is an amazing system! Let's examine each need and how it is met by the various systems of the body.
ATP is Energy!
For your muscles -- in fact, for every cell in your body -- the source of energy that keeps everything going is called ATP. Adenosine triphosphate (ATP) is the biochemical way to store and use energy.
The entire reaction that turns ATP into energy is a bit complicated, but here is a good summary:
-Chemically, ATP is an adenine nucleotide bound to three phosphates.
-There is a lot of energy stored in the bond between the second and third phosphate groups that can be used to fuel chemical reactions.
-When a cell needs energy, it breaks this bond to form adenosine diphosphate (ADP) and a free phosphate molecule.
-In some instances, the second phosphate group can also be broken to form adenosine monophosphate (AMP).
-When the cell has excess energy, it stores this energy by forming ATP from ADP and phosphate.
ATP is required for the biochemical reactions involved in any muscle contraction. As the work of the muscle increases, more and more ATP gets consumed and must be replaced in order for the muscle to keep moving.
Because ATP is so important, the body has several different systems to create ATP. These systems work together in phases. The interesting thing is that different forms of exercise use different systems, so a sprinter is getting ATP in a completely different way from a marathon runner!
ATP comes from three different biochemical systems in the muscle, in this order:
-1. phosphagen system
-2. glycogen-lactic acid system
-3. aerobic respiration
Let's look at each one in detail.
Phosphagen System
A muscle cell has some amount of ATP floating around that it can use immediately, but not very much -- only enough to last for about three seconds. To replenish the ATP levels quickly, muscle cells contain a high-energy phosphate compound called creatine phosphate. The phosphate group is removed from creatine phosphate by an enzyme called creatine kinase, and is transferred to ADP to form ATP. The cell turns ATP into ADP, and the phosphagen rapidly turns
the ADP back into ATP. As the muscle continues to work, the creatine phosphate levels begin to decrease. Together, the ATP levels and creatine phosphate levels are called the phosphagen system. The phosphagen system can supply the energy needs of working muscle at a high rate, but only for 8 to 10 seconds.
Glycogen-Lactic Acid System
Muscles also have big reserves of a complex carbohydrate called glycogen. Glycogen is a chain of glucose molecules. A cell splits glycogen into glucose. Then the cell uses anaerobic metabolism (anaerobic means "without oxygen") to make ATP and a byproduct called lactic acid from the glucose.
About 12 chemical reactions take place to make ATP under this process, so it supplies ATP at a slower rate than the phosphagen system. The system can still act rapidly and produce enough ATP to last about 90 seconds. This system does not need oxygen, which is handy because it takes the heart and lungs some time to get their act together. It is also handy because the rapidly contracting muscle squeezes off its own blood vessels, depriving itself of oxygen-rich blood.
There is a definite limit to anaerobic respiration because of the lactic acid. The acid is what makes your muscles hurt. Lactic acid builds up in the muscle tissue and causes the fatigue and soreness you feel in your exercising muscles.
Aerobic Respiration
By two minutes of exercise, the body responds to supply working muscles with oxygen. When oxygen is present, glucose can be completely broken down into carbon dioxide and water in a process called aerobic respiration. The glucose can come from three different places:
-remaining glycogen supplies in the muscles
-breakdown of the liver's glycogen into glucose, which gets to working muscle through the bloodstream
-absorption of glucose from food in the intestine, which gets to working muscle through the bloodstream
Aerobic respiration can also use fatty acids from fat reserves in muscle and the body to produce ATP. In extreme cases (like starvation), proteins can also be broken down into amino acids and used to make ATP. Aerobic respiration would use carbohydrates first, then fats and finally proteins, if necessary. Aerobic respiration takes even more chemical reactions to produce ATP than either of the above systems. Aerobic respiration produces ATP at the slowest rate of the three systems, but it can continue to supply ATP for several hours or longer, so long as the fuel supply lasts.
So imagine that you start running. Here's what happens:
-The muscle cells burn off the ATP they have floating around in about 3 seconds.
-The phosphagen system kicks in and supplies energy for 8 to 10 seconds. This would be the major energy system used by the muscles of a 100-meter sprinter or weight lifter, where rapid acceleration, short-duration exercise occurs.
-If exercise continues longer, then the glycogen-lactic acid system kicks in. This would be true for short-distance exercises such as a 200- or 400-meter dash or 100-meter swim.
-Finally, if exercise continues, then aerobic respiration takes over. This would occur in endurance events such as 800-meter dash, marathon run, rowing, cross-country skiing and distance skating.
From: http://www.howstuffworks.com/sports-physiology.htm/printable
Creatine is a peptide (small protein) made from the amino acids glycine, arginine and methionine. The average 70 kilogram male contains 120 grams of creatine, 95% of which is in skeletal muscle. Stores of creatine are maintained from ingestion of fish and meat products, as well as from production in the liver. Oral ingestion of excess creatine has been shown to reversibly inhibit its production in the liver and, once our skeletal muscles become saturated with creatine, the excess is filtered by the kidneys, then removed in the urine. Conversely, an absence of creatine from our diet, as occurs in strict vegetarians, results in sub-optimal muscle concentrations, indicating that our liver is not capable of making all the creatine required for smoothly functioning skeletal muscles.
Our body stores energy for later use within the molecular phosphate bonds of ATP (adenosine triphosphate) molecules. When energy is required, a molecule of phosphorus is removed from ATP resulting in ADP (adenosine diphosphate), phosphorus, and energy. ATP is therefore similar to a battery in that it can supply energy on demand. Approximately 60-70% of muscle creatine is similarly phosphorylated, providing a second source of energy storage.
As our skeletal muscles deplete their stores of ATP during activity, the phosphocreatine molecules pass their stored energy to ADP, resulting in a rapid replenishment of ATP. The theory behind creatine supplementation is that by increasing our stores of phosphocreatine in skeletal muscle, more energy will ultimately be available during periods of exercise.
From: http://www.koryubudo.com/articles/health-6.htm
The total amount of muscle proteins in mammals, including man, exceeds that of any other protein. About 40 percent of the body weight of a healthy human adult weighing about 70 kilograms (150 pounds) is muscle, which is composed of about 20 percent muscle protein. Thus, the human body contains about five to six kilograms (11 to 13 pounds) of muscle protein. An albumin-like fraction of these proteins, originally called myogen, contains various enzymes; phosphorylase, aldolase, glyceraldehyde phosphate dehydrogenase, and others; it does not seem to be involved in contraction. The globulin fraction contains myosin, the contractile protein, which also occurs in blood platelets, small bodies found in blood. The contractile proteins are soluble in salt solutions and susceptible to enzymatic digestion. The energy required for muscle contraction is provided by the oxidation of carbohydrates or lipids. The term mechano-chemical reaction has been used for this conversion of chemical into mechanical energy. Although the molecular process underlying the reaction is not yet completely understood, it is known to involve the fibrous muscle proteins, the peptide chains of which undergo a change in conformation during contraction.
Myosin, which can be removed from fresh muscle by adding it to a chilled solution of dilute potassium chloride and sodium bicarbonate, is insoluble in water. Myosin combines easily with another muscle protein called actin that forms 12 to 15 percent of the muscle proteins. Actin can exist in two forms: one, G-actin, is globular; the other, F-actin, is fibrous. Actomyosin is a complex molecule formed by one molecule of myosin and one or two molecules of actin. In muscle, actin and myosin filaments are oriented parallel to each other and to the long axis of the muscle. The actin filaments are linked to each other lengthwise by fine threads called S filaments. During contraction the S filaments shorten, so that the actin filaments slide toward each other, past the myosin filaments, thus causing a shortening of the muscle.
From: http://www.britannica.com/eb/print?eu=119723
Thick Filament: Composed of hundreds of long, contractile myosin molecules arranged in a staggered side by side complex.
Thin Filament: Composed of a linear array of hundreds of globular, actin monomers in a double helical arrangement.
Sarcomere: The unit of contractile activity composed mainly of actin and myosin and extending from Z line to Z line in a myofibril.
Myofibril: End to end arrays of identical sarcomeres.
Myofiber: A single multinucleated muscle cell containing all the usual cell organelles plus many myofibrils.
Muscle:
Organized arrays of muscle fibers.
From: http://www.indstate.edu/thcme/mwking/muscle.html#intro
As muscles age, they slowly change, however, strength levels are maintained throughout middle age, it is not until advanced age that muscle performance declines. From about age 60 on, muscle strength shows a steady decline. This condition has been called sarcopenia. Muscle atrophy and loss of strength, especially in the legs, can become pronounced in persons in their 70s, 80s and older. Research suggests that sarcopenia is caused by an overall slow down in the production of muscle proteins. However, it also appears that progressive resistance training can re-stimulate protein synthesis in muscle, even in extreme age. (Muscle and Nerve, January 2002).
The body is made up of a set of levers powered by muscles. Force is made possible through the arrangement of the muscles, bones and joints that make up the body's lever systems. Bones act as the levers, while joints perform as living fulcrums (like the center of a teeter-totter). Muscle, attached to bones by tendons and other connective tissue, exerts force by converting chemical energy into tension and contraction. When a muscle contracts, it shortens, in many cases pulling bone, like a lever across its hinge. Muscles move and by their motions we move. We are capable of performing a wide variety of actions, but despite this, muscle itself moves only by becoming shorter. They shorten and then they rest - in other words, a muscle can pull but it cannot push. We can see whole muscles contracting in this way but, in reality, they consist of millions of tiny, finely tuned protein filaments working together. Muscles commonly work in pairs called antagonistic pairs - one contracts (agonist) and one relaxes (antagonist).
When muscles contract the result is usually movement associated with the muscle length shortening. Exercises where the muscle length shortens are called concentric. There are two types of concentric muscle action, one called isotonic (muscular contraction in which the muscle remains under relatively constant tension while its length changes) and the other, isokinetic (exercise performed with a specialized apparatus that provides variable resistance to a movement, so that no matter how much effort is exerted, the movement takes place at a constant speed. Such exercise is used to test and improve muscular strength and endurance, especially after injury). Exercise where the muscle length becomes longer, it is called eccentric. In an isometric muscle action there is no change in muscle length.
Connections between joints, called "synovial joints," are fulcrums, the bones they connect are levers, and the muscles attached to them apply force (or resistance). An example of a first-class lever is the joint between the skull and the atlas vertebrae of the spine: the spine is the fulcrum across which muscles lift the head. An example of a second-class lever is the Achilles tendon, pushing or pulling across the heel of the foot. The elbow joint is an example of a third-class lever: when lifting a book, the elbow joint is the fulcrum across which the biceps muscle performs the work.
Muscle is attached to bone by tendons and other tissue and exerts force by converting chemical energy into tension and contraction. Muscles move and make us capable of a variety of actions, but muscle only really contracts and becomes shorter: they pull but they cannot push. Muscles often work at joints designed to be anchored by one muscle and pulled by another. Muscle is made up of millions of tiny protein filaments which work together to produce motion in the body. Nerves that link the muscle to the brain and spinal cord serve each muscle. Our bodily needs demand that muscles accomplish different chores, so we are equipped with three types of muscle: cardiac muscles, found only in the heart, and "smooth" muscles, which surround or are part of the internal organs. Both of these muscle types are involuntary and are not under any conscious control. The third type is muscle we use when we consciously move; they are called "skeletal" muscles. These muscles carry out voluntary movements and make up about 23% of the woman's body weight and about 40% of a man's and are the body's most abundant tissue.
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Image from the article. Click Here.
From: http://www.sciam.com/specialissues/0999bionic/0999zorpette.html
Go back to the Main overview page.
How do muscles work?
In order to understand muscle contraction we need to know a little about muscle
cell structure. A skeletal muscle is made up of long muscle fibres (muscle cells)
which, in turn, are composed of bundles of myofibrils (myo = muscle, fibrils
are threadlike strands of proteins). Each myofibril consists of two kinds of
protein filament (sometimes called myofilaments) - thick filaments made of myosin
and thin filaments made of actin. Myofilaments do not extend the full length
of a muscle fibre; they are stacked together in compartments called sarcomeres.
Sarcomeres are separated from one another by narrow zones of dense material
called Z lines.
Overview: The myosin heads extend and retract to form what are called cross bridges. These bridges "walk" along the actin fibers like the legs of a caterpillar walking along the ground (or think of the action of a boat's oars in the water). When the heads grab the actin and a bridge is formed, it acts to shorten the actin fibre, producing a contraction of the length of the overall muscle fibre. Contraction is the only movement a muscle can make, it can only contract and relax back to its original position (it can't expand or push). It is thought that these repetitive sliding movements produce the muscle contractions.
Sliding of the filaments depends on the interaction of actin and myosin molecules.
Myosin filaments are long and thin with rounded "heads" projecting out at the
sides. The myosin "heads" bind with ATP converting it to ADP using the energy
to alter their shape. The energized myosin can then bind to actin molecules
at specific sites forming cross-bridges.
A skeletal muscle contracts only when stimulated by a motor neurone. At rest, myosin is prevented from binding with actin molecules by the protein tropomyosin. Troponin controls the position of tropomyosin on the thin actin filament (not shown on the above diagram - tropomyosin wraps around the actin fibre like a vine on a tree). However following stimulation by a motor nerve, acetylcholine diffuses from the neurone triggering the release of calcium ions into the sarcoplasm. Calcium ions bind to the troponin which then act on the tropomyosin molecule exposing the myosin-binding sites. Once the binding sites are open the myosin molecules form cross-bridges with the actin and the two filaments slide over one another (the cross-bridges act rather like oars on a rowing boat sweeping the myosin molecule forwards). During relaxation, an active transport system pumps calcium back into the sarcoplasmic reticulum for storage.
There are a number of proteins involved in the overall process of nerve to muscle communication and in muscle contraction and recovery. If any of these proteins is defective in some way, the muscle can't function properly. In most cases, a protein defect results from a genetic defect in the code that spells out the structure and function of the protein. The "size" and impact of the defect determine the muscle disease and symptoms seen. In minor defects, a long term impact is seen and muscle damage slowly accumulates over years.
Click here to see the diagram by Dr. Barber at Pikeville College, KY. (From the website: http://www.embl-heidelberg.de/CellBiophys/LocalProbes/motorproteins/myosin.html#microbiology)
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Muscle is an excitable tissue, meaning that it can be stimulated mechanically, chemically or electrically to produce an action potential. An action potential is an electrical change across a cell membrane due to changes in the conduction of ions across the membrane. Nervous tissue is also an excitable tissue. Muscle cells contain a contractile mechanism that is activated by action potentials. There are about 630 muscles in the human body. About 40% of the body is skeletal muscle, add another 5-10 % for cardiac and smooth muscle.
Contraction by a whole muscle:
Isometric versus Isotonic: Isotonic contractions are those when the tension on a muscle remains constant but the muscle shortens as in lifting a static amount of weight. Isometric muscle contractions occur when the muscle doesn't shorten as, for example when pushing against an immovable object like a wall. Isometric contraction differs from isotonic in that the myofibrils don't slide over each other much as force is developed. Sliding does occur in isotonic contractions and external work is performed.
Motor unit concept: The motor nerve and all the fibers it innervates is called the motor unit. The number of fibers is dependent on the necessity for fine control. In general, small muscles that react rapidly with fine control have one nerve and only a few muscle fibers. Those muscles that do not require fine control, such as the gastrocnemius (calf muscle), may have several hundred muscle fibers per motor unit.
Summation: The contraction of individual muscle fibers is all-or- none. Therefore, any graded response must come from the number of motor units stimulated at any one time. Summation is the adding together of individual muscle twitches to make a whole muscle contraction. This can be accomplished by increasing the number of motor units contracting at one time (spatial summation) or by increasing the frequency of contraction of individual muscle contractions (temporal summation). These processes almost always occur simultaneously within normal muscle contraction. Usually, individual motor units fire asynchronously.
All motor units are not created equal. Therefore one motor unit within a particular muscle may be as much as 50 times as strong as another. Smaller motor units are much more easily excited than larger ones because they are innervated by smaller nerve fibers that have a naturally lower threshold for excitation. In spatial summation motor units are recruited by increasing the strength of the stimulus thereby increasing the strength of the contraction.
In temporal or wave summation the rapidity of each motor units contraction increases such that one contraction isn't completely over when the stimulus for the next arrives. So the force generated in the first is added to that generated by the second, third and so on. When a muscle is stimulated at progressively greater frequencies, a frequency is finally reached at which the successive contractions fuse together and cannot be distinguished one from the other. The muscle then enters a long continual state of maximal contraction called tetany.
Muscle Fatigue: Prolonged strong contractions leads to fatigue of the muscle caused by the inability of the contractile and metabolic processes to supply adequately to maintain the work load. The nerve continues to function properly passing the action potential onto the muscle fibers but the contractions become weaker and weaker due to the lack of ATP.
Hypertrophy: Muscle hypertrophy (increase in muscle mass) is caused by forceful muscular activity. The diameters of individual fibers increase, nutrient and metabolic substances increase, mitochondria may increase, and the myofibrils also increase in size and number. Muscular hypertrophy increases the power for muscle contraction and nutritive mechanisms for motioning that increased power. Forceful muscle activity, above 75% of maximal, is necessary to produce hypertrophy which is why isometric exercise for even short periods of time can have profound effects on muscle mass. However, prolonged light exercise increases endurance, causing increases in oxidative enzymes, myoglobin, and even blood capillaries.
Atrophy: Muscle atrophy results when a muscle is not used for a length of time or is used for only weak contractions. For instance, atrophy occurs when limbs are put in casts. As little as one month of disuse can sometimes decrease the muscle size to one half normal. Damage to the nerve to a muscle results atrophy a well. If the damage is repaired in the first 3-4 months the muscle will regain full function. After four months muscle fibers will have degenerated to fibrous and fatty tissue.
Muscle Types and Mechanism of Contraction
Skeletal Muscle
Skeletal muscle makes up most of the body's muscle and does not contract without nervous stimulation. It is under voluntary control and lacks anatomic cellular connections between fibers. The fibers (cells) are multinucleated and appear striated due to the arrangement of actin and myosin protein filaments. Each fiber is a single cell, long, cylindric and surrounded by a cell membrane. The muscle fibers contain many myofibrils that are made of myofilaments. These myofilaments are made of the contractile proteins. The key proteins in muscle contraction are myosin, actin, tropomyosin and troponin.
Skeletal muscle fibers have differences in metabolic and contractile properties. Type I fibers are mostly found in the muscle for posture as in the long muscles of the back. These are also called red muscles because the fibers contain many mitochondria that give the muscle more of a dark reddish hue. White muscles contain mostly Type IIB fibers and are specialized for fast, fine movements as in the muscles that move the eye or some hand muscles. The differences in fiber type occur because of differences in amino acid composition of the skeletal proteins without a change in biologic activity. Various forms of the proteins can be expressed thus determining the functional characteristics of each muscle. Changes in muscle function can be caused by alterations in activity (training), hormonal environment (steroids), or innervation. Skeletal muscle can undergo a limited regeneration in case of injury via satellite cells that are located on the periphery of the muscle fiber. These cells may be active in muscle hypertrophy as well. Contractile Proteins
Skeletal muscle is composed of cells, called fibers, that are specialized to contract or shorten in length. Each fiber is made of smaller subunits called myofibrils that are composed of contractile proteins called myosin and actin which are responsible for muscle contraction at the molecular level. These contractile protein filaments are also called thick (myosin) and thin (actin) filaments. These filaments interdigitate such that the proteins can interact. The myosin filaments have what are called cross bridges that stick out from the filament to interact with the actin filaments during contraction. Imagine a set of golf clubs held together by their shafts with the heads radiating out around the shafts. This is a visual picture of what the thick filaments look like. Because the clubs have different length shafts the heads stick out at different places along the cluster. The myosin filaments look like this on both ends of a long filament that is made of some 200 myosin protein molecules. This structure allows the myosin filament to pull the actin filaments from both directions thus shortening the fiber.
The actin filaments are composed of two strands of protein that are woven together as one. The actin filaments are anchored to Z lines that make the boundaries of the functional unit of muscle contraction called the sarcomere. There are many sarcomeres in a muscle fiber and Z lines are continuous across muscle fibers.
Sliding Filament Theory:
Muscle contraction occurs by a sliding filament mechanism whereby the sarcomeres shorten (the Z-lines come closer together) by the action of the actin filaments sliding over the myosin filaments. Myosin filaments may look somewhat like a golf club but they are not inflexible. In fact, muscle contraction would be impossible if the myosin molecules did not have a "hinge" along the shaft that allows for a ratchet movement of the head. The force behind muscle contraction is the ratchet movement of these tiny myosin heads toward the center of their sarcomere. This ratchet movement occurs many times during a muscle contraction.
The thin filaments are actually composed of more than just actin which forms the backbone of the filament. Two other proteins are part of the thin filaments, tropomyosin and troponin. Along the actin filaments there are active sites where myosin attaches during contraction. These active sites are covered in the relaxed state by tropomyosin so that contraction cannot occur. Troponin is a complex of three submits having different affinities. One has an affinity for actin, another for tropomyosin and a third for calcium. Troponin molecules are positioned along the actin- tropomyosin filaments and act to position the tropomyosin filaments over the active sites on the actin filaments. When calcium is present it binds to the troponin which changes in shape causing the movement of tropomyosin off the active sites so that myosin and actin can interact and muscle contraction can occur. When the active sites are uncovered the myosin heads bind to the sites which initiates a movement of the head toward the center of the sarcomere thus pulling the actin along and shortening the sarcomere. Each one of the myosin heads is thought to operate independently of the others, each attaching and pulling in a continuous alternating ratchet cycle until the calcium is removed and the active sites are covered up again.
Muscle contraction requires a great deal of energy. Energy is required to break the bond between the myosin head and the actin active sites as well as for removal of calcium from the cytoplasm by the use of a special pump within the sarcoplasmic reticulum. When the myosin head is tilted forward, after the power stroke, a binding site for ATP (the chief energy currency of the cell) is exposed. The breakdown of ATP to ADP releases the head from the actin filament and cocks it for the next ratchet power stroke.
Energy Sources
Energy is required for muscle contraction. At rest and during light exercise, muscles use lipids as their energy source. The use of carbohydrate becomes more important as the intensity of exercise increases. The breakdown of glucose to water and carbon dioxide generates energy that is transferred to regenerate phosphorylcreatine and ATP. When oxygen supplies are inadequate this process is short circuited and a metabolite (lactic acid) of one of the products builds up in the muscle. This is called anaerobic metabolism (glycolysis) and is a normal process that can occur prior to the oxidative breakdown of glucose. The lactate builds up in the muscles causing a change in pH that inhibits enzyme activity. After the exercise, an oxygen debt exists in that oxygen must be used to convert the lactate into carbon dioxide and water and replenish energy stores. Short intense exercise utilizes anaerobic metabolic mechanisms more than more sustained activities. For example, in a 100 m dash 85% of the energy is derived from anaerobic means while in a mile run only 20% is generated anaerobically.
Excitation-Contraction Coupling:
Contraction in skeletal muscle begins with an action potential in the muscle fiber. This causes the release of calcium from the sacroplasmic reticulum. The action potential in the muscle fiber begins after it is excited by interaction with a large insulated (myelinated) nerve fiber. The point of contact of the nerve and muscle is called the neuromuscular junction which is normally located in the middle of the muscle fiber. Therefore an action potential initiated here spreads toward the ends of the fiber making it possible for all sarcomeres to contract at the same time. Skeletal muscle has an adaptation that allows the action potential to spread deep within the fiber. The T or transverse tubules are internal extensions of the sarcolemma that penetrate through the fiber such that action potentials in the t-tubules cause the release of calcium from the nearby sarcoplasmic reticulum in the immediate vicinity of the myofibrils.
The sarcoplasmic reticulum contains calcium ions in very high concentration that are released when the adjacent T-tubule is excited. Pumps within the walls of the sarcoplasmic reticulum return the calcium within the cytoplasm to levels below those needed to activate the contractile process.
Neuromuscular Junction:
The association of the motor nerve and the muscle fiber occurs at the neuromuscular junction. Here, the neuron ends in a terminal button that contains small vesicles filled with the neurotransmitter acetylcholine. When an action potential reaches the terminal button the vesicles are released and the acetylcholine diffuses across a narrow space to bind to receptors on the muscle fiber cell membrane. When the acetylcholine binds to the receptors, the local permeability of the muscle cell membrane is altered so that an action potential is initiated on the muscle cell. This action potential then spreads over the muscle cell membrane and T-tubule system to initiate the contractile process. An enzyme called acetylcholinesterase is present within the neuromuscular junction to break down the acetylcholine and remove the stimulus to contract.
Smooth Muscle:
Smooth muscle is found in the walls of blood vessels, tubular organs such as the stomach and uterus, the iris, or associated with the hair follicles. It exists in the body as multiunit or visceral smooth muscle. It is not under voluntary control, each cell has one nucleus and it is displays automaticity in the visceral form. In multiunit smooth muscle each cell exists as a discreet independent unit that is innervated by a single nerve ending. Visceral smooth muscle exists as a sheet or bundle of fibers that are intimately connected by junctions that allow ions to flow freely and it therefore performs as a syncytium. Therefore, when one portion of visceral smooth muscle is stimulated the action potential spreads to all other fibers.
Most of the same contractile proteins are present and active in smooth muscle contraction but they are not arranged as microscopically visible parallel myofilaments as in skeletal muscle. The contractile mechanism is very similar to skeletal muscle except that the myosin of smooth muscle only interacts with actin when it has been phosphorylated. In smooth muscle calcium binds to a protein called calmodulin and the complex then interacts with an enzyme that adds a phosphate group to myosin thus activating it.
In smooth muscle, T-tubules are absent, the sarcoplasmic reticulum is poorly developed and the calcium pump is present but it is slower acting. Because of these differences in the contractile mechanism and machinery, smooth muscle takes about 30 times as long to contract and relax as does skeletal muscle and it does this while using much less energy. Elaborate neuromuscular junctions are not present in smooth muscle. Often neurotransmitter is released only in close proximity to the muscle such that the neurotransmitter, which may be acetylcholine or norepinephrine, must diffuse to the muscle cells to interact with receptors on the cell membrane. Either of these neurotransmitters may be excitatory or inhibitory depending on the receptors present on that particular smooth muscle cell. Because smooth muscle has spontaneous activity, neuronal input only serves to modify that activity rather than initiating it as in skeletal muscle. Local tissue factors, hormones and mechanical stretch can cause action potentials and thus contraction in smooth muscle. Smooth muscle is capable of active regeneration after injury.
Cardiac Muscle:
The heart is made of specialized muscle tissue with some similarities to both smooth and skeletal muscle. It is involuntary and mononucleate as is smooth muscle. Cardiac muscle is striated like skeletal muscle which means that it has microscopically visible myofilaments arranged in parallel with the sarcomere structure described above. These filaments slide along each other during the process of contraction in the same manner as occurs in skeletal muscle.
Cardiac muscle fibers branch and have a single nucleus per cell. Another difference in cardiac muscle is the presence of intercalated discs that are specialized connections between one cardiac muscle cell and another. These tight connections allow for almost completely free movement of ions so that action potentials can freely pass from one cell to another. This makes cardiac muscle tissue a functional syncytium. When one cell is excited the resultant action potential is spread to all of them. This is an important feature in that it allows the atrial or ventricular muscle to contract as one to forcefully pump blood. Action potentials in cardiac muscle are also specialized to maximize the pumping function of the heart. They last 10 to 30 times as long as those of skeletal muscle and cause a correspondingly increased period of contraction. Cardiac muscle had long been said to have no regenerative capacity beyond early childhood. Recently, however, evidence has been found to debunk this statement. There is strong evidence that human heart muscle regenerates to some degree by myocyte replication after cardiac injury.
Go back to the Main overview page.
There are a number of excellent web pages available. Please see them for more in-depth material.
Upper Extremity Muscle Atlas: http://www.rad.washington.edu/atlas/extpollbrevis.html
http://www.indstate.edu/thcme/mwking/muscle.html#intro
http://www.mpimf-heidelberg.mpg.de/~holmes/muscle/muscle1.html
Muscle Physiology Lab at the University of California, San Diego.
http://ortho84-13.ucsd.edu/musintro/Jump.shtml
Go back to the Main overview page.
Muscle tissue -- constitutes the bulk of the carcass of meat animals.
Skeletal muscle -- of principal interest to the meat industry. Muscle that is attached directly or indirectly to the skeleton.
Cardiac muscle -- muscle of the heart. Differentiated by the presence of intercalated disks.
Smooth muscle -- located in arteries and the lymph system as well as the digestive and reproduction systems. No real ordered
myofibrils and thus nonstriated appearance.
Skeletal muscle fiber terms
Sarcolemma -- membrane surrounding the muscle fiber.
Transverse tubules -- portion of the sarcoplasmic reticulum that stores and releases calcium during contraction and relaxation.
Myoneural junction -- where motor nerve endings terminate on the sarcolemma.
Motor end plate -- structure present at the myoneural junction that forms a small mound on the surface of the muscle fiber
Sarcoplasm -- cytoplasm of muscle fibers.
Nuclei -- "brain" of the cell. Muscle fibers contain many nuclei.
Myofibrils -- long, thin, cylindrical rods that run within and parallel to the long axis of the muscle
fiber.
Myofilaments -- comprised of thick and thin filaments. The thick are comprised of myosin and the thin are comprised of actin,
troponin, and tropomyosin.
Sarcomere -- the basic contractile unit of the muscle. Has Z-lines on either end along with A-band and two 1/2 I-bands.
Z-disk ultrastructure -- comprised of Z filaments. These are the connecting units between sarcomeres.
Proteins of the myofilament -- primarily actin and myosin (65% of total), but also include tropomyosin and troponin within the thin filament, C protein (which surrounds the myosin filaments to form the thick filaments), desmin (which encircles the Z disks and radiate out to connect adjacent myofibrils
Sarcoplasmic reticulum and T tubules -- membranous system of tubules and cisternae (flattened reservoirs for Ca++) that forms closely meshed network around each myofibril.
Mitochondria -- "powerhouse of the cell." Provides the cell with chemical energy.
Lysosomes -- small vesicles located in the sarcoplasm that contain a large number of enzymes collectively capable of digesting the cell and its contents. The best known of these are the cathepsins.
Golgi complex -- many of these are located in the muscle fiber and serve the same purpose as those in regular cells.
Connective tissue
Extracellular substance -- varies from a soft jelly to a tough fibrous mass.
Connective tissue proper -- fibrous connective tissue that surrounds muscles, muscle bundles and muscle fibers.
Supportive connective tissues -- bone and cartilage.
Ground substance -- viscous solution containing soluble glycoproteins (carbohydrate containing proteins) where the extracellular fibers are embedded.
Extracellular fibers -- Primarily comprised of collagen, elastin, and reticulin.
Adipose tissue
White versus brown fat -- most of adipose tissue in meat animals is white fat. Brown fat is mostly present in animals at birth.
Bone
Diaphysis -- long, central shaft of the bone.
Epiphyses -- enlargements on the ends of bones.
Periosteum -- thin membrane connective tissue covering of bone.
Articular cartilage -- present on the ends (joint) of bones. Comprised of hyaline cartilage.
Epiphyseal plate -- cartilaginous region separating the diaphysis and epiphysis.
Above from: http://savell-j.tamu.edu/structure.html
Size
Maximus=largest
Minimus=smallest
Longus=longest
Brevis=shortest
Number of origins
Biceps=two origins
Triceps=three origins
Quadriceps=four origins
Relative shape
Deltoid=triangular
Trapezius=trapezoid
Serratus=saw-toothed
Rhomboideus=rhomboid or diamond-shaped
Classification of Muscle Actions
-abductor = moves body part out
-adductor = draws body part in
-extensor = opens joint out (increases the angle at a joint)
-flexor = closes joint (decreases the angle at a joint)
-levator = raises a body part - upward movement
-depressor = lowers a body part - downward movement
-pronator = turns the palm downward
-supinator = turns the palm upward or anteriorly
-rotator = moves a bone around its longitudinal axis
-sphincter (constrictor) = decreases the size of an opening
-tensor = makes a body part more rigid
Muscle terminology glossary:
-Abductor (L. abducere, to move away). A muscle that draws a structure away from the axis of the body or one of its parts, e.g. lateral rectus muscle.
-Accessorius (L. accessorius, to move toward). Accessory or supernumerary. Also denoting specific muscles.
-Accessory (L. accessorius, to move toward). Supernumerary, adjuvant.
-Adductor (L. adducere, to bring forward). A muscle that draws a structure toward the axis of the body or one of its parts, e.g. adductor pollicis.
-Alae (L. ala, wing). Relating to a muscle of the nose, and others.
-Anconeus (G. ankon, elbow). Musculus anconeus.
-Ani (L. anus, anal oriface). Pertaining to a muscle that supports the anus.
-Anticus (L. anticus, anterior). Designating a muscle as placed anteriorly, e.g. serratus anterior.
-Arch (L. arcus, a bow). Any structure resembling a bent bow or an arch.
-Articulationis (L. articulationes, the forming of new joints of a vine). Pertaining to muscles that insert into a joint capsule.
-Arytenoid (G. arytenoideus, ladel-shaped). Pertaining to muscles attached to this laryngeal cartilage.
-Atlanto- (G. Atlas, in Greek mythology a Titan who supported the world on his shoulders). Relating to muscles attached to the second cervicle vertebra, the atlas.
-Atloideus. See Atlanto-
-Auricularis (L. auricularis, the external ear). Pertaining to muscles that attach to the external ear. Also referring to the fifth digit of the hand because of its use in cleaning the external auditory meatus.
-Axillary (L. axilla, armpit). Pertaining to muscles that are found in the region of the armpit, e.g. axillary arch muscle.
-Azygos (G. a, without + zygon, yoke). Any unpaired muscle.
-Basilaris (G., L., basis, base). Pertaining to the base, body, or lower part of a structure, e.g., base of the skull.
-Biceps (L. bi, two + caput, head). Two heads. Pertaining to muscles with two heads, e.g., biceps brachii.
-Biventer (L. bi, two + venter, belly). Muscle having two bellies.
-Brachialis (G. brachion, arm). Muscles relating to the arm.
-Brachii (G. brachion, arm). Muscles of the arm.
-Brachio- (G. brachion, arm) Relating to the arm.
-Brevis (L. brevis, short, brief). A short muscle or head, e.g., short head of biceps brachii.
-Buccinator (L. buccinator, trumpeter). A muscle of the cheek.
-Bucco- (L. bucca, cheek) Pertaining to the cheek.
-Bulbo- (L. bulbus, a bulbus root). Any globular or fusiform structurs. A muscle covering a bulbar structure.
-Capitis (L. caput, head). Pertaining to the head.
-Capsularis (L. capsa, a chest or box). A muscle joined to a capsule as, for example, a joint. Any structure so designated as a capsule.
-Carnosus (L. carnis, flesh or muscle). Pertaining to muscular tissue or dermal muscles.
-Carpi (G. karpos, wrist). Muscles relating to the eight carpal bones of the wrist.
-Caudatus (L. cauda, tail) The belly of a muscle. When the bellies are divided, bicaudatus.
-Cavernosus (L. caverna, a grotto or hollow). Pertaining to the cavernous tissue of the reproductive system.
-Cerato- (G. keras, horn). Relating to muscle that arises from the greater horn of the hyoid bone.
-Chondro- (G. chondros, cartilage). Pertaining to muscles that arise from costal cartilage.
-Cilii (L. cilium, eyelid). Pertaining to the eyebrow, e.g., corrigator supercilii.
-Clavicularis (L. clavicula, small key). Pertaining to muscles associated with the clavicle.
-Cleido- (G. kleis, clavicle). Related with the clavicle.
-Coccygeus (G. kokkyx, a cuckoo). A muscle associated with the coccyx, e.g., musculus coccygeus.
-Colli (L. collum, neck). Pertaining to the neck or to the neck of a structure, e.g., longus colli muscle.
-Communis (L. communis, in common). Relating to more than one structure working as one unit, e.g., extensor digitorum communis.
-Compressor (L. compressus, to press together). A muscle that, when contracted, produces pressure on another structure.
-Condyloideus (G. kondylos, knuckle). Pertaining to a muscle attached to the outer edge of a joint or a bony knob-like stucture.
-Constrictor (L. constringere). A muscle that, upon contraction, reduces the size of a canal, a sphincter.
-Coraco- (G. korakoides, a crow's beak). Denoting a muscle that arises from the coracoid process of the scapula.
-Cornu (L. cornu, horn). Any structure resembling a horn in shape.
-Corrugator (L. con, together + ruga, wrinkel). A muscle that wrinkels the skin.
-Costalis (L. costa, rib). Pertaining to muscles attached to ribs.
-Cremaster (G. kremaster, a suspender). Musculus cremaster, the muscle by which the testicles are suspended.
-Crico- (G. kikos, a ring). Denoting muscles that attach to the cricoid cartilage.
-Crural (L. crus, leg). Pertaining to the leg (from knee to ankle) or to any other muscle designated as a crus.
-Deltoideus (G. deltoeides, shaped like the letter delta). The musculus deltoideus, shaped like an inverted delta.
-Dentate (L. dentatus, toothed). Notched muscles, e.g., the serrati.
-Diaphragm (G. diaphragma, a partition). Muscle diaphragma separating the thorax from the abdomen.
-Digastricus (G. di, two + gaster, belly). Denoting muscles with two fleshy parts separated by a tendinous intersection, e.g., musculus digastricus.
-Dilatores (ME. dilaten, to dilate or expand). Denoting a muscle that opens an orifice.
-Dorso- (L. dorsum, back). Muscles related to the dorsal surface of the body, e.g., latissimus dorsi muscle. Also any structure related specifically to the thorax.
-Epi- (G. epi, upon). Denoting a muscle attached to another structure, e.g., dorsoepitrochlearis muscle.
-Epistropheus (G. epistropheus, the pivot). Muscles relating to the second cervical vertebra.
-Epitrochlearis (L. epi, upon + trochlearis, block or pulley). Pertaining to muscles associated with the humeral epichondyle.
-Extensor (L. ex-tendre, to stretch out). A muscle that , upon contraction, tends to straighten a limb. The antagonist of a flexor muscle.
-Femoris (L. femur, thigh). Pertaining to the femur or thigh.
-Flexor (L. flectere, to bend). A muscle that, upon contraction tends to bend a joint; the antagonist of an extensor.
-Gastrocnemius (G. gaster, belly + kneme, leg). The belly of the leg, e.g., musculus gastrocnemius.
-Gemelli (L. geminus, twin). The two gemelli, superior and inferior.
-Genio- (G. geneion, chin) Pertaining to muscles of the chin (mandible).
-Glosso- (G. glossa, tongue). Pertaing to a muscle that arises from, or inserts on, the tongue.
-Gluteus (G. gloutos, buttock). Pertaining to the muscles of the buttocks.
-Gracilis (L. gracilis, slender or delicate). Musculus gracilis of the thigh.
-Hallucis (L. hallux, great toe). The muscles and tendons associated with the first digit of the foot.
-Humero- (G. homos, shoulder). Pertaining to the bone of the arm and a muscles associated with it.
-Hyo- (G. hyoeides, hyoid). Relating to the U-shaped hyoid bone and muscles associated with it.
-Hyoideus. See Hyo- above.
-Iliacus (L. ilium, groin). A muscle of the groin.
-Ilio- (L. ilium, groin). Pertaining to a muscle of the groin and ilium.
-Indicis (L. index, one that points). The forefinger or pointer.
-Inferior (L. inferior, lower). Lower, caudal.
-Infra- (L. infra, below) Pertaining to a position below a named structure, e.g., infraspinatus.
-Internal (L. internus, interior). Deep or away from the surface.
-Inter (L. inter, between). Between or among.
-Ischio- (G. ischion, hip) Pertaining to the ischium.
-Lateral (L. lateralis, lateral). To the right or left of the axial line, to the outside, away from the midline.
-Latissimo- (L. latus, broad). A term applied to some broad flat muscles, e.g., latissimus dorsi.
-Levator (L. levare, to lift). One of several muscles whose function is to lift the structure to which it is attached, e.g., levator palpebrae superiorus.
-Linguae (L. lingua, tongue). Pertaining to, or toward, the tongue.
-Longissimus (L. longus, long). A name given to certain long muscles, e.g., longissimus capitis.
-Lumborum (L. lumbus, a loin) Pertaining to the back and sides between the pelvis and ribs.
-Lumbricales (L. lumbricus, an earthworm). Muscles resembling earthworms, e.g. the lumbricals.
-Mandibulo- (L. mandere, to chew). Pertaining to a muscle arising from the mandible.
-Manus (L. manus, hand). Pertaining to the muscles of the hand.
-Masseter (G. maseter, masticator). A large masticatory muscle of the jaw.
-Mastoideus (G. mastos, breast + eidos, resemblance). Resembling a mamma or a breast- shaped structure.
-Medial (L. medialis, middle). Relating to muscle nearer to the median or midsagittal plane.
-Mentalis (L. mentum, chin). Relating to the muscles of the chin, e.g., musculus mentalis.
-Mento- (L. mentum, chin). See Mentalis.
-Metacarpo- (G. meta, after + carpus, wrist). Pertaining to the bones adjacent to the wrist.
-Musculus (L. mus, mouse). A muscle.
-Myo- (G. mys, a muscle). Relating to a muscle.
-Mytiformis (G. mytilos, mussel + forma, shape). Shaped like the shellfish, e.g., musculus mytiformis.
-Naris (L. naris, nostril). Pertaining to muscles associated with the nostril.
-Nasalis (L. nasus, nose). Pertaining to the nose.
-Nuchae (F. nuque, back of the neck). Muscles associated with the back of the neck.
-Obturator (L. obturare, to occlude). Pertaining to muscles associated with the obturator membrane, which closes the obturator foramen.
-Occipitalis (L. ob, before or against + caput, head). Pertaining to muscles attached to the occipital bone.
-Omo (L. omo, shoulder). Pertaining to muscle attached to the scapula.
-Opponens ( L. opponere, to place against). A name given to several adductor muscles of the fingers and toes.
-Oris (L. oris, mouth). Relating to the entrance to the digestive tube, or mouth.
-Os (L. os, bone) a bone
-Palato- (L. palatum, palate). Relating to the hard or soft palate.
-Palmaris (L. palma, palm of the hand). Pertaining to muscles of the forearm, wihich may insert into the palmar aponeurosis.
-Palpebrae (L. palpebra, eyelid). The eyelid.
-Panniculus (L. pannus, cloth). Pertaining to a thin sheet of dermal muscle.
-Pectineus (L. pecten, a comb). Pertaining to the os pubis or any ridged structure. A muscle.
-Pectoro- (L.pectus, pector-, chest). Pertaining to the muscles of the chest wall.
-Pedis (L. pes, foot). Refering to the foot.
-Peroneus (G. perone, brooch or fibula). Pertaining to several muscles on the lateral or fibular side of the leg.
-Phalangei (F., G., L. phalanx, a formation of Roman soldiers). Pertaining to the bones of the fingers.
-Pharyngeus (G. pharynx, throat). Pertaining to the pharynx.
-Piriformis (L. pirum, pear + forma, shaped). Pear-shaped.
-Pisiform (L. pisum, pea + forma). Pea-shaped or pea sized.
-Plantaris (L. plantaris, sole of the foot) Pertaining to a muscle of the foot, musculus plantaris.
-Platysma (G. platys, flat or broad). A broad flat dermal muscle of the thorax and neck.
-Pollicis (L. pollex, thumb). Relating to the thumb.
-Popliteus (L. poples, the ham of the knee). Pertaining to a muscle of the popliteal space.
-Procerus (L. procerus, long or stretched-out). A muscle of the nose.
-Pronator (L. pronare, to bend forward). A muscle that, on contraction, rotates the hand so that the palm of the hand faces backward when the arm is in the anatomical position.
-Psoas (G. psoa, muscle of the loin). Pertaining to muscles in the lumbosacral region, the "tenderloin".
-Pterygoideus (G. pteryx, or pteryg-, wing + eidos, resemblance). Wing-shaped. Applied to muscles associated with the pterygoid processes of the sphenoid bone.
-Pubo- (L. pubes, genitalis). Pertaing to muscles attaching to the os pubis.
-Pyramidalis (G. pyramis, pyramid). Applied to muscles having, more or less, pyramidal shape.
-Quadratus (L. quadratus, square). More or less square-shaped muscles.
-Quadriceps (L. quadi-, four + caput, head). A name given to a muscle having four heads, e.g., quadriceps femoris.
-Quinti (L. quintus, fifth). Fifth, as in the fifth digit.
-Radio- (L. radius, ray). Pertaining to muscles associated with the radius of the forearm.
-Rectalis (L. rectus, straight). Pertaining to muscles associated with the distal segment of the large intestine.
-Rhombo- (G. rhombos, a rhomb). Resembling a rhomb, an oblique parallelogram of unequal sides. Relating to two superficial muscles of the back.
-Risorius (L. risor, laughter). Pertaining to a facial muscle, i.e., musculus risorius.
-Salpingo- (G. salpinx, trumpet). Pertaining to a muscle fascicle attached to the eustachian (auditory) tube and pharynx.
-Saphenous (G. saphenes, visible) Pertaining to a muscle that is associated with the saphenous vein.
-Sartorius (L. sartor, a tailor). Musculus sartorius.
-Scalenus (G. skalenos, uneven). Pertaining to muscles having uneven sides or length.
-Scapulo- (L. scapulae, shoulder blades). Pertaining to a muscle associated with the scapula.
-Semi- (L. semis, half). Prefix denoting half or partly.
-Serratus (L. serra, saw). Pertaining to muscles that are serrated, notched, or dentate.
-Soleus (L. solea, a sandal [foot]). Musculus soleus.
-Spinous (L. spina, thorn). Related to the spinous processes of the vertebral column.
-Splenius (G. splenion, a bandage). Musculus splenius and others.
-Stapedius (L. stapes, stirrup). A muscle inserted into the stapes. Musculus stapedius.
-Sterno- (G. sternon, the chest). Pertaining to muscles attached to the sternum.
-Stylo- (G. stylos, pillar or post). Pertaining to muscles attached to the styloid process of the temporal bone.
-Sub- (L. sub, under). Denoting muscles that are beneath or inferior to a named structure, e.g., subclavius.
-Superior (L. superus, above). Denoting a muscle located above another muscle in an inferior position or to another structure to which it is attached.
-Supinator (L. supinare, to place on back). Denoting a muscle that, upon contraction, rotates the forearm and hand with the palm facing anteriorly when the hand and forearm are in the anatomical position.
-Supra- (L. supra, above). Prefix to note the position of a muscle above a named structure, e.g., supracostalis.
-Suralis (L. sura, calf of the leg). Relating to the calf.
-Temporalis (L. tempus, time or temple). Relating to the temple, musculus temporalis.
-Tensor (L. tendere, to stretch). Pertaining to a muscle whose function is to make a structure, to which it is attached, firm and tense.
-Teres (L. tero, round or smooth). Denoting certain muscles that are round and long.
-Thyro- (G. thyreos, an oblong shield). Denoting certain muscles attached to the thyroid cartilage.
-Tibialis (L. tibia, a pipe or flute). Pertaining to muscles attached to the tibia.
-Trachelian (G. trachelos, neck). Pertaining to muscles associated with the neck.
-Transversus (L. trans, across + vertare, to turn). Denoting muscles that lie across the long axis of an organ or a part.
-Trapezius (G. trapezion, a table) A four sided muscle having no two sides that are parallel. Musculus trapezius.
-Triangularis (L. tri, three + angulus, angle). A muscle that is, more or less, triangular in shape.
-Triceps (L. tri, three + caput, head). Denoting a muscle with three heads, e.g., musculus triceps.
-Triticeo- (L. triticum, a grain of wheat). Pertaining to a muscle attached in part to the cartilago triticea.
-Ulnaris (L. ulna, elbow forearm). Pertaining to the larger and more medial of the two bones of the forearm.
-Uncinatus (L. uncus, hook). Os hamatum or unciform bone. A muscle attached to the hook of the hamate, e.g., pisiuncinatus.
-Urethrae (G. ourethra, urethra). Relating to the urethra, e. g., musculus sphincter urethrae.
-Vaginae (L. vagina, sheath). Pertaining to a muscle attached to a joint capsule.
-Vastus (L. vastus, huge). A large muscle of the thigh, musculus quadriceps with three vasti and a rectus.
-Zygomaticus (G. zygoma, a bar or bolt) Pertaining to the zygomatic bone, e.g., musculus zygomaticus.
-From: http://www.vh.org/Providers/Textbooks/AnatomicVariants/Terminology.html
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I highly recommend the reader investigates the outstanding site on musculature and the descriptions available on Wikipedia at the following link: http://en.wikipedia.org/wiki/List_of_muscles_of_the_human_body
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There are several excellent web sites listing and showing all of the muscles.
Here is a comprehensive site:
http://www.meddean.luc.edu/lumen/MedEd/GrossAnatomy/ From there, click on master muscle list.
The Hosford Muscle Tables (a comprehensive site):
http://www.ptcentral.com/muscles/
LUMEN's Master Muscle List (a comprehensive site): http://www.meddean.luc.edu/lumen/MedEd/GrossAnatomy/dissector/muscles/mus_ue.html
Here is another, excellent, simple site on muscles (unfortunately these are
the folks that I received a nasty letter from as explained above):
http://www.innerbody.com/image/musfov.html
As an alternative, I highly recommend the reader investigates the outstanding
site on musculature and the descriptions available on Wikipedia at the following
link: http://en.wikipedia.org/wiki/List_of_muscles_of_the_human_body
Go back to the Main overview page.
An excellent book on muscles for the "general reader" has recently come out:
Prime Mover: A Natural History of Muscle
by Steven Vogel, Annette Deferrari (Illustrator) 2001 W.W. Norton & Company; ISBN 0393021262
Here is a book review from Amazon.com
Beneath the skin of a human being's inner upper arm, some metaphorically minded ancient Greek once observed, lives a little mouse. In Latin, this imagined creature, evident in the bump of the biceps, was called musculus, the origin of our word muscle. It's a staggeringly complex animal, we learn from this vivid exploration of the muscular world--one that requires much care and feeding, and that repays that attention with endless, efficient energy.
Biologist and bioengineer Steven Vogel takes us deep within our bodies, observing humansand other animals at rest and work to show how muscles expand and (sort of) contract, how our proprioceptive system coordinates that motion, how bodily mass relates to metabolism, and many other matters. Muscle is, of course, meat, and Vogel closes his book with a discussion of why meat has so long been prized in the human diet--and why today we can do without it and still keep the motor running.
Vogel's book is a fine example of how complex science can be made comprehensible to nonspecialists--and just the thing for a budding physiologist. --Gregory McNamee
A comprehensive textbook of muscles and their pathology (geared towards the expert):
Karpati, G., Hilton-Jones, D., Griggs, R. C. (Eds) (Seventh Edition) (2001). Disorders of Voluntary Muscle. Cambridge U. K.: Cambridge University Press.
From Book News, Inc. A comprehensive reference-text on disorders of muscle for clinicians, first published in 1964 and most recently in 1988. The structure of the previous edition is retained, with sections devoted respectively to anatomy, physiology, and biochemistry; pathology; clinical problems in neuromuscular disease; and electrodiagnosis. This updated edition adds two co-editors, George Karpati and David Hilton-Jones. Among the changes in this edition are new chapters on the cell biology of muscle; the molecular biology of muscle; the light microscopic morphological abnormalities in skeletal muscle disease; metabolic and endocrine myopathies; mitochondrial and lipid storage diseases of muscle; and myasthenia and related disorders.
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Encyclopaedia Britannica. http://www.britannica.com/
American Heritage Collegiate Dictionary. (via http://www.bartleby.com )
Columbia Encyclopaedia. (via http://www.bartleby.com )
Gray's Anatomy. (via http://www.bartleby.com )
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