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Encyclopedia > Muscle
A top-down view of skeletal muscle
A top-down view of skeletal muscle

Muscle (from Latin musculus, diminutive of mus "mouse"[1]) is contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to produce force and cause motion. Muscles can cause either locomotion of the organism itself or movement of internal organs. Cardiac and smooth muscle contraction occurs without conscious thought and is necessary for survival. Examples are the contraction of the heart and peristalsis which pushes food through the digestive system. Voluntary contraction of the skeletal muscles is used to move the body and can be finely controlled. Examples are movements of the eye, or gross movements like the quadriceps muscle of the thigh. There are two broad types of voluntary muscle fibers: slow twitch and fast twitch. Slow twitch fibers contract for long periods of time but with little force while fast twitch fibers contract quickly and powerfully but fatigue very rapidly. http://training. ... http://training. ... For other uses, see Latins and Latin (disambiguation). ... A top-down view of skeletal muscle A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. ... Biological tissue is a group of cells that perform a similar function. ... Organs derived from each germ layer. ... For other uses, see Force (disambiguation). ... This article or section is in need of attention from an expert on the subject. ... In biology, an organ is a group of tissues which perform some function. ... Consciousness is a quality of the mind generally regarded to comprise qualities such as subjectivity, self-awareness, sentience, sapience, and the ability to perceive the relationship between oneself and ones environment. ... The heart and lungs, from an older edition of Grays Anatomy. ... Peristalsis is the rhythmic contraction of smooth muscles to propel contents through the digestive tract. ... what was here was sick and improperly spelled. ... Quads redirects here. ... In humans the thigh is the area between the pelvis and buttocks and the knee. ...



Types of muscle
Types of muscle

There are three types of muscle: Image File history File links Illu_muscle_tissues. ... Image File history File links Illu_muscle_tissues. ...

  • Skeletal muscle or "voluntary muscle" is anchored by tendons to bone and is used to affect skeletal movement such as locomotion and in maintaining posture. Though this postural control is generally maintained as a subconscious reflex, the muscles responsible react to conscious control like non-postural muscles. An average adult male is made up of 40–50% of skeletal muscle and an average adult female is made up of 30–40% (as a percentage of body mass).[citation needed]
  • Smooth muscle or "involuntary muscle" is found within the walls of organs and structures such as the esophagus, stomach, intestines, bronchi, uterus, urethra, bladder, blood vessels, and even the skin (in which it controls erection of body hair). Unlike skeletal muscle, smooth muscle is not under conscious control.
  • Cardiac muscle is also an "involuntary muscle" but is more akin in structure to skeletal muscle, and is found only in the heart.

Cardiac and skeletal muscles are "striated" in that they contain sarcomeres and are packed into highly-regular arrangements of bundles; smooth muscle has neither. While skeletal muscles are arranged in regular, parallel bundles, cardiac muscle connects at branching, irregular angles (called intercalated discs). Striated muscle contracts and relaxes in short, intense bursts, whereas smooth muscle sustains longer or even near-permanent contractions. A top-down view of skeletal muscle Skeletal muscle is a type of striated muscle, usually attached to the skeleton. ... A tendon or sinew is a tough band of fibrous connective tissue, attached on one end to a muscle and on the other to a bone. ... This article is about the skeletal organs. ... For other uses, see Skeleton (disambiguation). ... In a general sense, locomotion simply means active movement or travel, applying not just to biological individuals. ... Smooth muscle Layers of Esophageal Wall: 1. ... The esophagus or oesophagus (see American and British English spelling differences), sometimes known as the gullet, is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. ... In anatomy, the stomach is a bean-shaped hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication. ... In anatomy, the intestine is the segment of the alimentary canal extending from the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine. ... A bronchus (plural bronchi, adjective bronchial) is a caliber of airways in the the respiratory tract that conducts air into the lungs. ... This article is about female reproductive anatomy. ... In anatomy, the urethra (from Greek ουρήθρα - ourethra) is a tube which connects the urinary bladder to the outside of the body. ... This article is about the urinary bladder. ... f you all The blood vessels are part of the circulatory system and function to transport blood throughout the body. ... Cardiac muscle is a type of involuntary striated muscle found within the heart. ... Image of sarcomere A sarcomere is the basic unit of a cross striated muscles myofibril. ...

Skeletal muscle is further divided into several subtypes:

  • Type I, slow oxidative, slow twitch, or "red" muscle is dense with capillaries and is rich in mitochondria and myoglobin, giving the muscle tissue its characteristic red color. It can carry more oxygen and sustain aerobic activity.
  • Type II, fast twitch muscle, has three major kinds that are, in order of increasing contractile speed:[2]
    • Type IIa, which, like slow muscle, is aerobic, rich in mitochondria and capillaries and appears red.
    • Type IIx (also known as type IId), which is less dense in mitochondria and myoglobin. This is the fastest muscle type in humans. It can contract more quickly and with a greater amount of force than oxidative muscle, but can sustain only short, anaerobic bursts of activity before muscle contraction becomes painful (often incorrectly attributed to a build-up of lactic acid). N.B. in some books and articles this muscle in humans was, confusingly, called type IIB.[3]
    • Type IIb, which is anaerobic, glycolytic, "white" muscle that is even less dense in mitochondria and myoglobin. In small animals like rodents this is the major fast muscle type, explaining the pale color of their flesh.

The word capillary is used to describe any very narrow tube or channel through which a fluid can pass. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... An X-ray diffraction image for the protein myoglobin. ... This article is about the chemical element and its most stable form, or dioxygen. ... This article or section should include material from aerobic respiration. ... For other uses, see Fermentation. ... For the production of milk by mammals, see Lactation. ... Glycolysis is the sequence of reactions that converts glucose into pyruvate with the concomitant production of a relatively small amount of ATP. The word is derived from Greek γλυκύς (sweet) and λύσις (letting loose). ...


The anatomy of muscles includes both gross anatomy, comprising all the muscles of an organism, and, on the other hand, microanatomy, which comprises the structures of a single muscle. The 1989 movie Gross Anatomy stars Matthew Modine and Daphne Zuniga. ... A thin section of lung tissue stained with hematoxylin and eosin. ...

Gross anatomy

Muscles, anterior view (See Gray's muscle pictures for detailed pictures)
Muscles, anterior view (See Gray's muscle pictures for detailed pictures)
Muscles, posterior view (See Gray's muscle pictures for detailed pictures)
Muscles, posterior view (See Gray's muscle pictures for detailed pictures)

The gross anatomy of a muscle is the single most important indicator of its role in the body. The action a muscle generates is determined by the origin and insertion locations. The cross-sectional area of a muscle (rather than volume or length) determines the amount of force it can generate by defining the number of sarcomeres which can operate in parallel. The amount of force applied to the external environment is determined by lever mechanics, specifically the ratio of in-lever to out-lever. For example, moving the insertion point of the biceps more distally on the radius (farther from the joint of rotation) would increase the force generated during flexion (and, as a result, the maximum weight lifted in this movement), but decrease the maximum speed of flexion. Moving the insertion point proximally (closer to the joint of rotation) would result in decreased force but increased velocity. This can be most easily seen by comparing the limb of a mole to a horse - in the former, the insertion point is positioned to maximize force (for digging), while in the latter, the insertion point is positioned to maximize speed (for running). // Grays figure #361 Grays figure #362 Grays figure #363 Grays figure #364 Grays figure #365 Grays figure #366 Grays figure #367 Grays figure #368 Grays figure #369 Grays figure #370 Grays figure #371 Grays figure #372 Grays... // Grays figure #361 Grays figure #362 Grays figure #363 Grays figure #364 Grays figure #365 Grays figure #366 Grays figure #367 Grays figure #368 Grays figure #369 Grays figure #370 Grays figure #371 Grays figure #372 Grays...

One particularly important aspect of gross anatomy of muscles is pennation or lack thereof. In most muscles, all the fibers are oriented in the same direction, running in a line from the origin to the insertion. In pennate muscles, the individual fibers are oriented at an angle relative to the line of action, attaching to the origin and insertion tendons at each end. Because the contracting fibers are pulling at an angle to the overall action of the muscle, the change in length is smaller, but this same orientation allows for more fibers (thus more force) in a muscle of a given size. Pennate muscles are usually found where their length change is less important than maximum force, such as the rectus femoris.

There are approximately 639 skeletal muscles in the human body. However, the exact number is difficult to define because different sources group muscles differently.

Main article: Table of muscles of the human body

This is a table of muscles of the human anatomy. ...


Muscle is mainly composed of muscle cells. Within the cells are myofibrils; myofibrils contain sarcomeres, which are composed of actin and myosin. Individual muscle fibres are surrounded by endomysium. Muscle fibers are bound together by perimysium into bundles called fascicles; the bundles are then grouped together to form muscle, which is enclosed in a sheath of epimysium. Muscle spindles are distributed throughout the muscles and provide sensory feedback information to the central nervous system. Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... A diagram of the structure of a Myofybril Myofibrils (obsolete term: sarcostyles) are cylindrical organelles, found within muscle cells. ... G-Actin (PDB code: 1j6z). ... Myosin is a motor protein filament found in muscle tissue. ... The endomysium, literally meaning within the muscle, is a layer of connective tissue that ensheaths a muscle fiber and is composed mostly from reticular fibers. ... Perimysium is a sheath of connective tissue which groups individual muscle fibers ( anywhere between 10 to 100 or more) into bundles or fascicles Endomysium Histology at cytochemistry. ... Fascicles are sections of a book, usually a reference work, that because of its length, is issued in parts so that the information may be made available to the public as soon as possible rather than waiting years or decades to complete the entire work. ... Epimysium is a layer of connective tissue which ensheaths the entire muscle. ... A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ... A diagram showing the CNS: 1. ...

Skeletal muscle is arranged in discrete muscles, an example of which is the biceps brachii. It is connected by tendons to processes of the skeleton. Cardiac muscle is similar to skeletal muscle in both composition and action, being comprised of myofibrils of sarcomeres, but anatomically different in that the muscle fibers are typically branched like a tree and connect to other cardiac muscle fibers through intercalcated discs, and form the appearance of a syncytium. In human anatomy, the biceps brachii is a muscle located on the upper arm. ... For other uses, see Tendon (disambiguation). ... An intercalated disc is an undulating double membrane separating adjacent cells in cardiac muscle fibers. ... In biology, a syncytium is a large region of cytoplasm that contains many nuclei. ...


Main article: muscle contraction

The three (skeletal, cardiac and smooth) types of muscle have significant differences. However, all three use the movement of actin against myosin to create contraction. In skeletal muscle, contraction is stimulated by electrical impulses transmitted by the nerves, the motor nerves and motoneurons in particular. Cardiac and smooth muscle contractions are stimulated by internal pacemaker cells which regularly contract, and propagate contractions to other muscle cells they are in contact with. All skeletal muscle and many smooth muscle contractions are facilitated by the neurotransmitter acetylcholine. A top-down view of skeletal muscle A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. ... A top-down view of skeletal muscle A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. ... A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ... For other uses, see Nerve (disambiguation). ... In vertebrates, motoneurons (also called motor neurons) are efferent neurons that originate in the spinal cord and synapse with muscle fibers to facilitate muscle contraction and with muscle spindles to modify proprioceptive sensitivity. ... Chemical structure of D-aspartic acid, a common amino acid neurotransmitter. ... The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. ...

Muscular activity accounts for much of the body's energy consumption. All muscle cells produce adenosine triphosphate (ATP) molecules which are used to power the movement of the myosin heads. Muscles conserve energy in the form of creatine phosphate which is generated from ATP and can regenerate ATP when needed with creatine kinase. Muscles also keep a storage form of glucose in the form of glycogen. Glycogen can be rapidly converted to glucose when energy is required for sustained, powerful contractions. Within the voluntary skeletal muscles, the glucose molecule can be metabolized anaerobically in a process called glycolysis which produces two ATP and two lactic acid molecules in the process (note that in aerobic conditions, lactate is not formed; instead pyruvate is formed and transmitted through the citric acid cycle). Muscle cells also contain globules of fat, which are used for energy during aerobic exercise. The aerobic energy systems take longer to produce the ATP and reach peak efficiency, and requires many more biochemical steps, but produces significantly more ATP than anaerobic glycolysis. Cardiac muscle on the other hand, can readily consume any of the three macronutrients (protein, glucose and fat) aerobically without a 'warm up' period and always extracts the maximum ATP yield from any molecule involved. The heart, liver and red blood cells will also consume lactic acid produced and excreted by skeletal muscles during exercise. Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer. ... Creatine, or creatine monohydrate [NH2-C(NH)-NCH2(COOH)-CH3], is a naturally occurring compound that helps to supply energy to the muscle cells. ... Creatine Kinase Creatine kinase (CK), also known as phosphocreatine kinase or creatine phosphokinase (CPK) is an enzyme (EC 2. ... Glycogen Structure Segment Glycogen is a polysaccharide of glucose (Glc) which functions as the primary short term energy storage in animal cells. ... Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. ... Overview of the citric acid cycle The citric acid cycle (also known as the tricarboxylic acid cycle, the TCA cycle, or the Krebs cycle, after Hans Adolf Krebs who identified the cycle) is a series of chemical reactions of central importance in all living cells that use oxygen as part... Aerobic exercise refers to exercise that is of moderate intensity, undertaken for a long duration. ...

Nervous control

Efferent leg

The efferent leg of the peripheral nervous system is responsible for conveying commands to the muscles and glands, and is ultimately responsible for voluntary movement. Nerves move muscles in response to voluntary and autonomic (involuntary) signals from the brain. Deep muscles, superficial muscles, muscles of the face and internal muscles all correspond with dedicated regions in the primary motor cortex of the brain, directly anterior to the central sulcus that divides the frontal and parietal lobes. Efferent nerve fibers carry information away from the central nervous system. ... The Peripheral nervous system resides or extends outside the CNS central nervous system (the brain and spinal cord) to serve the limbs and organs. ... For other uses, see Nerve (disambiguation). ... The somatic nervous system is that part of the peripheral nervous system associated with the voluntary control of body movements through the action of skeletal muscles, and also reception of external stimuli. ... This article or section is in need of attention from an expert on the subject. ... For other uses, see Brain (disambiguation). ... A human brain. ...

In addition, muscles react to reflexive nerve stimuli that do not always send signals all the way to the brain. In this case, the signal from the afferent fiber does not reach the brain, but produces the reflexive movement by direct connections with the efferent nerves in the spine. However, the majority of muscle activity is volitional, and the result of complex interactions between various areas of the brain. A reflex action is an automatic (involuntary) neuromuscular action elicited by a defined stimulus. ... The Spinal cord nested in the vertebral column. ...

Nerves that control skeletal muscles in mammals correspond with neuron groups along the primary motor cortex of the brain's cerebral cortex. Commands are routed though the basal ganglia and are modified by input from the cerebellum before being relayed through the pyramidal tract to the spinal cord and from there to the motor end plate at the muscles. Along the way, feedback, such as that of the extrapyramidal system contribute signals to influence muscle tone and response. Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria For the folk-rock band see The Mammals. ... The primary motor area is a group of networked cells in mammalian brains that controls movements of specific body parts associated with cell groups in that area of the brain. ... For other uses, see Cortex. ... The basal ganglia (or basal nuclei) are a group of nuclei in the brain interconnected with the cerebral cortex, thalamus and brainstem. ... The cerebellum (Latin: little brain) is a region of the brain that plays an important role in the integration of sensory perception and motor control. ... The corticospinal or pyramidal tract is a massive collection of axons that travel between the cerebral cortex of the brain, and the spinal cord. ... The Spinal cord nested in the vertebral column. ... A motor end plate is the innervation of a muscle fiber which causes muscle contraction. ... In human anatomy, the extrapyramidal system is a neural network located in the brain that is part of the motor system involved in the coordination of movement. ...

Deeper muscles such as those involved in posture often are controlled from nuclei in the brain stem and basal ganglia. While not moving, a human can be in one of the following main positions. ... The brain stem is the lower part of the brain, adjoining and structurally continuous with the spinal cord. ...

Afferent leg

The afferent leg of the peripheral nervous system is responsible for conveying sensory information to the brain, primarily from the sense organs like the skin. In the muscles, the muscle spindles convey information about the degree of muscle length and stretch to the central nervous system to assist in maintaining posture and joint position. The sense of where our bodies are in space is called proprioception, the perception of body awareness. More easily demonstrated than explained, proprioception is the "unconscious" awareness of where the various regions of the body are located at any one time. This can be demonstrated by anyone closing their eyes and waving their hand around. Assuming proper proprioceptive function, at no time will the person lose awareness of where the hand actually is, even though it is not being detected by any of the other senses. ... A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ... This article is about the senses of living organisms (vision, taste, etc. ... // Proprioception (PRO-pree-o-SEP-shun (IPA pronunciation: ); from Latin proprius, meaning ones own and perception) is the sense of the relative position of neighbouring parts of the body. ...

Several areas in the brain coordinate movement and position with the feedback information gained from proprioception. The cerebellum and red nucleus in particular continuously sample position against movement and make minor corrections to assure smooth motion. The red nucleus is a structure in the rostral midbrain involved in motor coordination. ...


Exercise is often recommended as a means of improving motor skills, fitness, muscle and bone strength, and joint function. Exercise has several effects upon muscles, connective tissue, bone, and the nerves that stimulate the muscles. A motor skill is a skill that requires an organism to utilize their skeletal muscles effectively in a goal directed manner. ... Physical fitness is an attribute required for service in virtually all military forces. ... Connective tissue is one of the four types of tissue in traditional classifications (the others being epithelial, muscle, and nervous tissue. ...

Various exercises require a predominance of certain muscle fiber utilization over another. Aerobic exercise involves long, low levels of exertion in which the muscles are used at well below their maximal contraction strength for long periods of time (the most classic example being the marathon). Aerobic events, which rely primarily on the aerobic (with oxygen) system, use a higher percentage of Type I (or slow-twitch) muscle fibers, consume a mixture of fat, protein and carbohydrates for energy, consume large amounts of oxygen and produce little lactic acid. Anaerobic exercise involves short bursts of higher intensity contractions at a much greater percentage of their maximum contraction strength. Examples of anaerobic exercise include sprinting and weight lifting. The anaerobic energy delivery system uses predominantly Type II or fast-twitch muscle fibers, relies mainly on ATP or glucose for fuel, consumes relatively little oxygen, protein and fat, produces large amounts of lactic acid and can not be sustained for as long a period as aerobic exercise. The presence of lactic acid has an inhibitory effect on ATP generation within the muscle; though not producing fatigue, it can inhibit or even stop performance if the intracellular concentration becomes too high. However, long-term training causes neovascularization within the muscle, increasing the ability to move waste products out of the muscles and maintain contraction. Once moved out of muscles with high concentrations within the sarcomere, lactic acid can be used by other muscles or body tissues as a source of energy, or transported to the liver where it is converted back to pyruvate. The ability of the body to export lactic acid and use it as a source of energy depends on training level. For other senses of this word, see Marathon (disambiguation). ... Weightlifting is a sport where competitors attempt to lift heavy weights mounted on steel bars. ... Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. ... Pyruvate (CH3COCOO−) is the ionized form of pyruvic acid. ...

Humans are genetically predisposed with a larger percentage of one type of muscle group over another. An individual born with a greater percentage of Type I muscle fibers would theoretically be more suited to endurance events, such as triathlons, distance running, and long cycling events, whereas a human born with a greater percentage of Type II muscle fibers would be more likely to excel at anaerobic events such as a 200 meter dash, or weightlifting. People with high overall musculation and balanced muscle type percentage engage in sports such as rugby or boxing and often engage in other sports to increase their performance in the former.[citations needed] For other uses, see Rugby (disambiguation). ... For other meanings of these words, see boxing (disambiguation) or boxer. ...

Delayed onset muscle soreness is pain or discomfort that may be felt one to three days after exercising and subsides generally within two to three days later. Once thought to be caused by lactic acid buildup, a more recent theory is that it is caused by tiny tears in the muscle fibers caused by eccentric contraction, or unaccustomed training levels. Since lactic acid disperses fairly rapidly, it could not explain pain experienced days after exercise.[4] Delayed Onset Muscle Soreness (DOMS) is the pain or discomfort often felt 24 to 72 hours after exercising and subsides generally within 2 to 3 days. ... A top-down view of skeletal muscle A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. ...


Main article: Neuromuscular disease

Symptoms of muscle diseases may include weakness, spasticity, myoclonus and myalgia. Diagnostic procedures that may reveal muscular disorders include testing creatine kinase levels in the blood and electromyography (measuring electrical activity in muscles). In some cases, muscle biopsy may be done to identify a myopathy, as well as genetic testing to identify DNA abnormalities associated with specific myopathies and dystrophies. Neuromuscular disease is a very broad term that encompasses many diseases and ailments that either directly, via intrinsic muscle pathology, or indirectly, via nerve pathology, impair the functioning of the muscles. ... Weakness can mean: The opposite of strength Weakness (medical) This is a disambiguation page — a navigational aid which lists pages that might otherwise share the same title. ... Spasticity is a disorder of the bodys motor system,and especially the Central Nervous Systems (CNS), in which certain muscles are continuously contracted. ... Myoclonus is brief, involuntary twitching of a muscle or a group of muscles. ... Myalgia means muscle pain and is a symptom of many diseases and disorders. ... Electromyography (EMG) is a technique for evaluating and recording physiologic properties of muscles at rest and while contracting. ... In medicine, a muscle biopsy is a procedure in which a piece of muscle tissue is removed from an organism and examined microscopically. ... In medicine, a myopathy is a neuromuscular disease in which the muscle fibers do not function for any one of many reasons, resulting in muscular weakness. ... Genetic testing allows the genetic diagnosis of vulnerabilities to inherited diseases, and can also be used to determine a persons ancestry. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Muscular dystrophy refers to a group of genetic, hereditary muscle diseases that cause progressive muscle weakness. ...

Neuromuscular diseases are those that affect the muscles and/or their nervous control. In general, problems with nervous control can cause spasticity or paralysis, depending on the location and nature of the problem. A large proportion of neurological disorders leads to problems with movement, ranging from cerebrovascular accident (stroke) and Parkinson's disease to Creutzfeldt-Jakob disease. Neuromuscular disease is a very broad term that encompasses many diseases and ailments that either directly, via intrinsic muscle pathology, or indirectly, via nerve pathology, impair the functioning of the muscles. ... Paralysed redirects here. ... Neurology is a branch of medicine dealing with disorders of the central and peripheral nervous systems. ... A stroke or cerebrovascular accident (CVA) occurs when the blood supply to a part of the brain is suddenly interrupted by occlusion (an ischemic stroke- approximately 90% of strokes), by hemorrhage (a hemorrhagic stroke - less than 10% of strokes) or other causes. ... Creutzfeldt-Jakob disease (CJD) is a very rare and incurable degenerative neurological disorder (brain disease) that is ultimately fatal. ...

A non-invasive elastography technique that measures muscle noise is undergoing experimentation to provide a way of monitoring neuromuscular disease. The sound produced by a muscle comes from the shortening of actomyosin filaments along the axis of the muscle. During contraction, the muscle shortens along its longitudinal axis and expands across the transverse axis, producing vibrations at the surface.[5] Elastography is an emerging method in which stiffness or strain images of soft tissue are used to detect tumors. ... Actomyosin is a protein complex composed of Actin and Myosin. ... Look up Contraction in Wiktionary, the free dictionary. ... This page is a candidate for speedy deletion. ... Vibrations are massage movements carried out using the fingertips and palmar surface of the hands. ...


There are many diseases and conditions which cause a decrease in muscle mass, known as muscle atrophy. Example include cancer and AIDS, which induce a body wasting syndrome called cachexia. Other syndromes or conditions which can induce skeletal muscle atrophy are congestive heart disease and some diseases of the liver. // Clinical settings of atrophy There are many diseases and conditions which cause a decrease in muscle mass, known as atrophy. ... Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ... For other uses, see AIDS (disambiguation). ... Congestive heart failure (CHF), also called congestive cardiac failure (CCF) or just heart failure, is a condition that can result from any structural or functional cardiac disorder that impairs the ability of the heart to fill with or pump a sufficient amount of blood through the body. ... // Acute hepatitis A Acute hepatitis B Acute Hepatitis D -this is actually a superinfection with the delta-agent in a patient already infected with hepatitis B Acute hepatitis C Acute hepatitis E Chronic viral hepatitis Other viral hepatitis virusses may exist but are not so firmly established as the previous...

During aging, there is a gradual decrease in the ability to maintain skeletal muscle function and mass, known as sarcopenia. The exact cause of sarcopenia is unknown, but it may be due to a combination of the gradual failure in the "satellite cells" which help to regenerate skeletal muscle fibers, and a decrease in sensitivity to or the availability of critical secreted growth factors which are necessary to maintain muscle mass and satellite cell survival. Sarcopenia is a normal aspect of aging, and is not actually a disease state. Please wikify (format) this article as suggested in the Guide to layout and the Manual of Style. ...

Physical inactivity and atrophy

Inactivity and starvation in rodents and mammals lead to atrophy of skeletal muscle, accompanied by a smaller number and size of the muscle cells as well as lower protein content.[6] In humans, prolonged periods of immobilization, as in the cases of bed rest or astronauts flying in space, are known to result in muscle weakening and atrophy. Such consequences are also noted in small hibernating mammals like the golden-mantled ground squirrels and brown bats.[7] Representatives of the Ursid species make for an interesting exception to this expected norm.

Bears are famous for their ability to survive unfavorable environmental conditions of low temperatures and limited nutrition availability during winter by means of hibernation. During that time Ursids go through a series of physiological, morphological and behavioral changes.[8] Their ability to maintain skeletal muscle number and size at time of disuse is of a significant importance. During hibernation bears spend four to seven months of inactivity and anorexia without undergoing muscle atrophy and protein loss.[7] There are a few known factors that contribute to the sustaining of muscle tissue. During the summer period, Ursids take advantage of the nutrition availability and accumulate muscle protein. The protein balance of bears at time of dormancy is also maintained by lower levels of protein breakdown during the winter time.[7] At times of immobility, muscle wasting in Ursids is also suppressed by a proteolytic inhibitor that is released in circulation.[6] Another factor that contributes to the sustaining of muscle strength in hibernating bears is the occurrence of periodic voluntary contractions and involuntary contractions from shivering during torpor.[9] The 3 to 4 daily episodes of muscle activity are responsible for the maintenance of muscle strength and responsiveness in bears during hibernation.[9]


A display of "strength" (e.g lifting a weight) is a result of three factors that overlap: physiological strength (muscle size, cross sectional area, available crossbridging, responses to training), neurological strength (how strong or weak is the signal that tells the muscle to contract), and mechanical strength (muscle's force angle on the lever, moment arm length, joint capabilities). Contrary to popular belief, the number of muscle fibres cannot be increased through exercise; instead the muscle cells simply get bigger. Muscle fibres have a limited capacity for growth through hypertrophy and some believe they split through hyperplasia if subject to increased demand. U.S. Marine emerging from the swim portion of a triathlon. ... Bodybuilder Markus Rühl has marked hypertrophy of skeletal muscle. ... Hyperplasia (or hypergenesis) is a general term referring to the proliferation of cells within an organ or tissue beyond that which is ordinarily seen in e. ...

The "strongest" human muscle

Since three factors affect muscular strength simultaneously and muscles never work individually, it is unrealistic to compare strength in individual muscles, and state that one is the "strongest". But below are several muscles whose strength is noteworthy for different reasons.

  • In ordinary parlance, muscular "strength" usually refers to the ability to exert a force on an external object—for example, lifting a weight. By this definition, the masseter or jaw muscle is the strongest. The 1992 Guinness Book of Records records the achievement of a bite strength of 4337 N (975 lbf) for 2 seconds. What distinguishes the masseter is not anything special about the muscle itself, but its advantage in working against a much shorter lever arm than other muscles.
  • If "strength" refers to the force exerted by the muscle itself, e.g., on the place where it inserts into a bone, then the strongest muscles are those with the largest cross-sectional area. This is because the tension exerted by an individual skeletal muscle fiber does not vary much. Each fiber can exert a force on the order of 0.3 micronewton. By this definition, the strongest muscle of the body is usually said to be the quadriceps femoris or the gluteus maximus.
  • A shorter muscle will be stronger "pound for pound" (i.e., by weight) than a longer muscle. The myometrial layer of the uterus may be the strongest muscle by weight in the human body. At the time when an infant is delivered, the entire human uterus weighs about 1.1 kg (40 oz). During childbirth, the uterus exerts 100 to 400 N (25 to 100 lbf) of downward force with each contraction.
  • The external muscles of the eye are conspicuously large and strong in relation to the small size and weight of the eyeball. It is frequently said that they are "the strongest muscles for the job they have to do" and are sometimes claimed to be "100 times stronger than they need to be." However, eye movements (particularly saccades used on facial scanning and reading) do require high speed movements, and eye muscles are exercised nightly during rapid eye movement sleep.
  • The statement that "the tongue is the strongest muscle in the body" appears frequently in lists of surprising facts, but it is difficult to find any definition of "strength" that would make this statement true. Note that the tongue consists of sixteen muscles, not one.
  • The heart has a claim to being the muscle that performs the largest quantity of physical work in the course of a lifetime. Estimates of the power output of the human heart range from 1 to 5 watts. This is much less than the maximum power output of other muscles; for example, the quadriceps can produce over 100 watts, but only for a few minutes. The heart does its work continuously over an entire lifetime without pause, and thus does "outwork" other muscles. An output of one watt continuously for eighty years yields a total work output of two and a half gigajoules.

In human anatomy, the masseter is one of the muscles of mastication. ... Human jaw front view Human jaw left view Human jaw top view The jaw is either of the two opposable structures forming, or near the entrance to, the mouth. ... Suresh Joachim, minutes away from breaking the ironing world record at 55 hours and 5 minutes, at Shoppers World, Brampton. ... For other uses, see Newton (disambiguation). ... The pound-force is a non-SI unit of force or weight (properly abbreviated lbf or lbf). The pound-force is equal to a mass of one pound multiplied by the standard acceleration due to gravity on Earth (which is defined as exactly 9. ... A simplified, global view of a neuromuscular junction: 1. ... Muscles of the iliac and anterior femoral regions. ... The gluteus maximus is the largest of the gluteus muscles which are located in the buttock. ... For other uses, see Mass (disambiguation). ... “Baby” redirects here. ... For other uses, see Eye (disambiguation). ... A saccade is a fast movement of an eye, head, or other part of an animals body or of a device. ... Rapid eye movement (REM) sleep is the normal stage of sleep characterized by rapid movements of the eyes. ... For other uses, see Tongue (disambiguation). ... The heart and lungs, from an older edition of Grays Anatomy. ... For other uses, see Watt (disambiguation). ... Quads redirects here. ... Look up gigajoule in Wiktionary, the free dictionary. ...


The efficiency of human muscle has been measured (in the context of rowing and cycling) at 14% to 27%. The efficiency is defined as the ratio of mechanical work output to the total metabolic cost.[citation needed] In physics, mechanical efficiency is the effectiveness of a machine and is defined as Efficiency is often indicated by a percentage, the efficiency of an ideal machine is 100%. Due to the fact that energy cannot emerge from nothing and the Second law of thermodynamics which states that the quality... Rowing in the Amstel River by a student rowing club. ... Cycling is the use of bicycles, unicycles, tricycles, quadricycles and other similar wheeled human powered vehicles (HPVs) as a means of transport, a form of recreation or a sport. ... In physics, mechanical work is the amount of energy transferred by a force. ... Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ...

Density of muscle tissue compared to adipose tissue

The density of mammalian skeletal muscle tissue is about 1.06 kg/liter[10]. This can be contrasted with the density of adipose tissue (fat), which is 0.9196 kg/liter[11]. This makes muscle tissue approximately 15% denser than fat tissue. For other uses, see Density (disambiguation). ... Adipose tissue is one of the main types of connective tissue. ...

Muscle evolution

Evolutionarily, specialized forms of skeletal and cardiac muscles predated the divergence of the vertebrate/arthropod evolutionary line.[12] This indicates that these types of muscle developed in a common ancestor sometime before 700 million years ago (mya). Vertebrate smooth muscle (smooth muscle found in humans) was found to have evolved independently from the skeletal and cardiac muscles. Cardiac muscle is a type of involuntary striated muscle found within the heart. ... This article does not cite any references or sources. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ... An ancestor is a parent or (recursively) the parent of an ancestor (i. ... For other uses of mya, see mya (disambiguation). ...

See also

Look up muscle in
Wiktionary, the free dictionary.
Wikimedia Commons has media related to:

Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Web-based project to create a free content dictionary, available in over 151 languages. ... Fascia is specialized connective tissue layer which surrounds muscles, bones, and joints, providing support and protection and giving structure to the body. ... Professional Bodybuilder Gustavo Badell posing Bodybuilding is the process of maximizing muscle hypertrophy through the combination of weight training, sufficient caloric intake, and rest. ... This is a list of muscles of the human anatomy. ... In medicine, a myopathy is a neuromuscular disease in which the muscle fibers do not function for any one of many reasons, resulting in muscular weakness. ... Myotomy describes a surgical procedure in which muscle is cut. ... Rapid plant movement encompasses movement in plant structures occurring over a very short period of time, usually under one second. ... Atrophy is the partial or complete wasting away of a part of the body. ... // Clinical settings of atrophy There are many diseases and conditions which cause a decrease in muscle mass, known as atrophy. ... Bodybuilder showing highly developed muscle tone. ... Electroactive Polymers or EAPs are polymers whose shape is modified when a voltage is applied to them. ... It has been suggested that this article or section be merged with Procedural memory. ... The musculoskeletal system (also known as the locomotor system) is an organ system that gives animals the ability to physically move using the muscles and skeletal system. ...


  1. ^ Definition and origin of the word 'muscle'
  2. ^ Larsson, L; Edstrom L, Lindegren B, Gorza L, Schiaffino S (July 1991). "MHC composition and enzyme-histochemical and physiological properties of a novel fast-twitch motor unit type". The American Journal of Physiology 261 (1 pt 1): C93–101. PMID 1858863. Retrieved on 2006-06-11. 
  3. ^ Smerdu, V; Karsch-Mizrachi I, Campione M, Leinwand L, Schiaffino S (December 1994). "Type IIx myosin heavy chain transcripts are expressed in type IIb fibers of human skeletal muscle". The American Journal of Physiology 267 (6 pt 1): C1723–1728. PMID 7545970. Retrieved on 2006-06-11.  Note: Access to full text requires subscription; abstract freely available
  4. ^ Robergs R, Ghiasvand F, Parker D (2004). "Biochemistry of exercise-induced metabolic acidosis.". Am J Physiol Regul Integr Comp Physiol 287 (3): R502-16. PMID 15308499. 
  5. ^ 'Muscle noise' could reveal diseases' progression 18 May 2007, NewScientist.com news service, Belle Dumé
  6. ^ a b Fuster G, Busquets S, Almendro V, López-Soriano FJ, Argilés JM (2007). "Antiproteolytic effects of plasma from hibernating bears: a new approach for muscle wasting therapy?". Clin Nutr 26 (5): 658-61. doi:10.1016/j.clnu.2007.07.003. PMID 17904252. 
  7. ^ a b c Lohuis TD, Harlow HJ, Beck TD (2007). "Hibernating black bears (Ursus americanus) experience skeletal muscle protein balance during winter anorexia". Comp. Biochem. Physiol. B, Biochem. Mol. Biol. 147 (1): 20-8. doi:10.1016/j.cbpb.2006.12.020. PMID 17307375. 
  8. ^ Carey HV, Andrews MT, Martin SL (2003). "Mammalian hibernation: cellular and molecular responses to depressed metabolism and low temperature". Physiol. Rev. 83 (4): 1153-81. doi:10.1152/physrev.00008.2003. PMID 14506303. 
  9. ^ a b Harlow, H.J.; Lohuis, T.; Anderson-sprecher, R.C.; Beck, T.D.I. (2004). "Body Surface Temperature Of Hibernating Black Bears May Be Related To Periodic Muscle Activity". Journal of Mammalogy 85 (3): 414-419. doi:10.1644/1545-1542(2004)085< . 
  10. ^ Urbancheka M, Pickenb E, Kaliainenc L, Kuzon W (2001). "Specific Force Deficit in Skeletal Muscles of Old Rats Is Partially Explained by the Existence of Denervated Muscle Fibers. [1]". The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 56:B191-B197. 
  11. ^ Farvid M, Ng, T, Chan D, Barrett P, Watts G. "Association of adiponectin and resistin with adipose tissue compartments, insulin resistance and dyslipidaemia. [[2]]". 
  12. ^ Evolution of muscle fibers

Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 162nd day of the year (163rd in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 162nd day of the year (163rd in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...


  • Costill, David L and Wilmore, Jack H. (2004). Physiology of Sport and Exercise. Champaign, Illinois: Human Kinetics. ISBN 0-7360-4489-2.
  • Phylogenetic Relationship of Muscle Tissues Deduced from Superimposition of Gene Trees, Satoshi OOta and Naruya Saitou, Mol. Biol. Evol. 16(6) 856–7, 1999
  • Johnson George B. (2005) "Biology, Visualizing Life." Holt, Rinehart, and Winston. ISBN 0-03-016723-X

Dr George B. Johnson, (born 11 June 1952, Newport News, Virginia, is a science writer who wrote the weekly column On Science in the St. ...

External links

  • Muslumova, Irada (2003). Power of a Human Heart. The Physics Factbook. (Heart output 1.3 to 5 watts, lifetime output 2 to 3 ×109 joules)
  • University of Dundee article on performing neurological examinations (Quadriceps "strongest")
  • Muscle efficiency in rowing
  • Human Muscle Tutorial (clear pictures of main human muscles and their Latin names, good for orientation)
  • Microscopic stains of skeletal and cardiac muscular fibers to show striations. Note the differences in myofibrilar arrangements.
The dorsal interossei, four in number, are situated between the metatarsal bones. ... The Plantar interossei muscles is a muscle of the human body. ...

  Results from FactBites:
Muscle - Home (298 words)
MUSCLE is an EC-sponsored Network of Excellence that aims at establishing and fostering closer collaboration between research groups in multimedia datamining and machine learning.
In particular, MUSCLE researchers are developing software tools and research strategies to enable users to move away from labor-intensive case-by-case modelling of individual applications, and allow them to take full advantage of generic adaptive and self-learning solutions that need minimal supervision.
MUSCLE has launched several SHOWCASING projects destined to produce higlhy visual demonstrations of the Multimedia expertise of the different teams involed in the Network of Excellence.
Your Multitalented Muscles (1120 words)
Muscles are all made of the same material, a type of elastic tissue (sort of like the material in a rubber band).
Smooth muscles are sometimes also called involuntary muscles and they are usually in sheets, or layers, with one layer of muscle behind the other.
Muscles in your neck and the top part of your back aren't as large, but they are capable of some pretty amazing things: Try rotating your head around, back and forth, and up and down to feel the power of the muscles in your neck.
  More results at FactBites »



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