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. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. A muscles contraction (also known as a muscle twitch or simply twitch) occurs when a Muscle fibre generates tension through the action of Actin Tissue is a cellular organizational level intermediate between cells and a complete organism A germ layer is a collection of cells formed during animal Embryogenesis. 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. In Physics, a force is whatever can cause an object with Mass to Accelerate. In Physics, motion means a constant change in the location of a body Muscles can cause either locomotion of the organism itself or movement of internal organs. In Biology, an organ ( Latin: organum, "instrument tool" from Greek όργανον - organon "organ instrument Cardiac and smooth muscle contraction occurs without conscious thought and is necessary for survival. Consciousness has been defined loosely as a constellation of attributes of Mind such as Subjectivity, Self-awareness, Sentience, and the Examples are the contraction of the heart and peristalsis which pushes food through the digestive system. The heart is a muscular organ in all Vertebrates responsible for pumping Blood through the Blood vessels by repeated rhythmic In the Esophagus After food is chewed into a bolus it is swallowed to move it into the esophagus Digestion is the breaking down of chemicals in the body into a form that can be absorbed 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. "Quads" redirects here For other uses see Quad The quadriceps femoris ( Latin for "four-headed of the femur" also In humans the thigh is the area between the Pelvis and the Knee. 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.

Types

Types of muscle

There are three types of muscle:

• 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. Skeletal muscle is a type of Striated muscle, which usually attaches to tendons A tendon (or sinew) is a tough band of Fibrous connective tissue that usually connects Muscle to Bone and is capable of withstanding tension Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce In Biology, the skeleton is a strong and often a rigid framework that supports the body of an animal holding it upright and giving it shape and strength (Also skeletal 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).
• 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). Smooth muscle is a type of non- Striated muscle, found within the Tunica media layer of large and small Arteries and Veins, the bladder The esophagus or oesophagus (see American and British English spelling differences) sometimes known as the gullet, is an organ in In Human anatomy, the stomach is a J-shaped hollow muscular organ of the Gastrointestinal tract involved in the second phase of Digestion, following 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 A bronchus (plural bronchi, adjective bronchial) is a caliber of airway in the Respiratory tract that conducts air into the Lungs No Gas The uterus (from the Latin word for womb) is the major Female reproductive organ of most Mammals including Humans One end the In Anatomy, the urethra (from Greek ουρήθρα - ourethra) is a tube which connects the Urinary bladder to the outside of In Anatomy, the urinary bladder is a hollow muscular, and distensible (or elastic organ that sits on the Pelvic floor in Mammals It is the The blood vessels are part of the Circulatory system and function to transport Blood throughout the body 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. The cardiac muscle is a type of involuntary striated Muscle found in the walls of 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. "A-band" redirects here For other uses of the term see A band. 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.

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. Capillaries are the smallest of a body's Blood vessels measuring 5-10 μm in diameter which connect Arterioles and Venules and enable the interchange In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. Myoglobin is a single-chain globular Protein of 153 Amino acids containing a Heme ( Iron -containing Porphyrin) Prosthetic It can carry more oxygen and sustain aerobic activity. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Cellular respiration is the set of the metabolic reactions and processes that take place in Organisms cells to convert biochemical energy from
• 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). Fermentation is the process of deriving energy from the oxidation of organic compounds such as carbohydrates using an endogenous electron acceptor which is Lactic acid ( IUPAC Systematic name: 2-hydroxypropanoic acid) also known as milk acid, is a Chemical compound that plays a role 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. See also Gluconeogenesis, which carries out a process wherein glucose is synthesized rather than catabolized In small animals like rodents this is the major fast muscle type, explaining the pale color of their flesh.

Anatomy

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. Gross anatomy is the study of Anatomy at the macroscopic level. Histology (from the Greek = 'tissue' is the study of the microscopic anatomy of cells and tissues of Plants and

Gross anatomy

Muscles, anterior 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 most important indicator of its role in the body. Mechanics of muscle ( Mechanics of muscle ( 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).

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

Microanatomy

Muscle is mainly composed of muscle cells. This is a table of Muscles of the Human anatomy. There are approximately 640 Skeletal muscles within the typical human and almost every muscle constitutes one The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called Within the cells are myofibrils; myofibrils contain sarcomeres, which are composed of actin and myosin. Myofibrils (obsolete term sarcostyles) are cylindrical Organelles found within Muscle cells They are bundles of actomyosin filaments Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of Myosins are a large family of Motor proteins found in Eukaryotic tissues. Individual muscle fibres are surrounded by endomysium. 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 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. Perimysium is a sheath of Connective tissue which groups individual Muscle fibers (anywhere between 10 to 100 or more into bundles or fascicles See Epimysium is a layer of Connective tissue which ensheaths the entire Muscle. Muscle spindles are distributed throughout the muscles and provide sensory feedback information to the central nervous system. Muscle spindles are Sensory receptors within the belly of a Muscle, which primarily detect changes in the length of this muscle In Vertebrates the central nervous system ( CNS) is the part of the Nervous system which is enclosed in the Meninges.

Skeletal muscle is arranged in discrete muscles, an example of which is the biceps brachii. In Human anatomy, the biceps brachii is a Muscle located on the upper Arm. It is connected by tendons to processes of the skeleton. A tendon (or sinew) is a tough band of Fibrous connective tissue that usually connects Muscle to Bone and is capable of withstanding tension 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. An intercalated disc is an undulating double membrane separating adjacent cells in Cardiac muscle fibers In Biology, a syncytium ( plural syncytia) is a large cell-like structure filled with Cytoplasm containing many nuclei

Physiology

Main article: muscle contraction

The three (skeletal, cardiac and smooth) types of muscle have significant differences. A muscles contraction (also known as a muscle twitch or simply twitch) occurs when a Muscle fibre generates tension through the action of Actin However, all three use the movement of actin against myosin to create contraction. A muscles contraction (also known as a muscle twitch or simply twitch) occurs when a Muscle fibre generates tension through the action of Actin In skeletal muscle, contraction is stimulated by electrical impulses transmitted by the nerves, the motor nerves and motoneurons in particular. In Neurophysiology, the action potential is a self-regenerating Wave of Electrochemical activity that allows Nerve cells to carry a signal A nerve is an enclosed cable-like bundle of peripheral Axons (the long slender projections of Neurons. In Vertebrates the term motor neuron (or motoneuron) classically applies to Neurons located in the Central nervous system (or CNS that project 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. See Chemical synapse for an introduction to concepts and terminology used in this article The Chemical compound acetylcholine (often abbreviated ACh) is a Neurotransmitter in both the Peripheral nervous system (PNS and Central

Muscular activity accounts for much of the body's energy consumption. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός All muscle cells produce adenosine triphosphate (ATP) molecules which are used to power the movement of the myosin heads. Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy Muscles conserve energy in the form of creatine phosphate which is generated from ATP and can regenerate ATP when needed with creatine kinase. Phosphocreatine, also known as creatine phosphate or Pcr, is a phosphorylated Creatine molecule that is an important energy store in skeletal Creatine kinase (CK also known as creatine phosphokinase (CPK or phosphocreatine kinase, is an Enzyme ( expressed by various tissue types Muscles also keep a storage form of glucose in the form of glycogen. Glycogen is a Polysaccharide of Glucose (Glc which functions as the secondary short term energy storage in Animal cells Glycogen can be rapidly converted to glucose when energy is required for sustained, powerful contractions. Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. 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). Pyruvic acid (CH3COCO2H is an alpha-keto acid. The Carboxylate Anion of pyruvic acid is known as pyruvate. The citric acid cycle, also known as the tricarboxylic acid cycle ( TCA cycle) or the Krebs cycle, (or rarely the Szent-Györgyi–Krebs cycle Muscle cells also contain globules of fat, which are used for energy during aerobic exercise. Aerobic exercise refers to Exercise that involves or improves oxygen consumption by the body 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.

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. In the Nervous system, efferent nerves – otherwise known as motor or effector Neurons – carry nerve impulses away from the The peripheral nervous system ( PNS) resides or extends outside the Central nervous system (CNS which consists of the Brain and Spinal cord. Nerves move muscles in response to voluntary and autonomic (involuntary) signals from the brain. A nerve is an enclosed cable-like bundle of peripheral Axons (the long slender projections of Neurons. "Somatic" redirects here for the musician known as Somatic see Hahn Rowe. &trade The autonomic nervous system ( ANS) (or visceral nervous system) is the part of the Peripheral nervous system that acts as a Control The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a 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. The human brain controls the Central nervous system (CNS by way of the Cranial nerves and Spinal cord, the Peripheral nervous system (PNS

In addition, muscles react to reflexive nerve stimuli that do not always send signals all the way to the brain. A reflex action, also known as a reflex, is an involuntary and almost instant movement in response to stimulus. 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. The spinal cord is a long thin tubular bundle of Nerves that is an extension of the Central nervous system from the brain and is enclosed in and protected However, the majority of muscle activity is volitional, and the result of complex interactions between various areas of the brain.

Nerves that control skeletal muscles in mammals correspond with neuron groups along the primary motor cortex of the brain's cerebral cortex. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands The primary motor cortex (or M1) works in association with pre-motor areas to plan and execute movements The cerebral cortex is a structure within the Brain that plays a key role in Memory, Attention, perceptual Awareness, Thought, 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. The basal ganglia (or basal nuclei) are a group of nuclei in the Brain interconnected with the Cerebral cortex, Thalamus and The cerebellum ( Latin: "little brain" is a region of the Brain that plays an important role in the integration of sensory perception The corticospinal or pyramidal tract is a massive collection of Axons that travel between the Cerebral cortex of the Brain and the Spinal The spinal cord is a long thin tubular bundle of Nerves that is an extension of the Central nervous system from the brain and is enclosed in and protected A neuromuscular junction ( NMJ) is the Synapse or junction of the Axon terminal of a Motoneuron with the motor end plate, the Along the way, feedback, such as that of the extrapyramidal system contribute signals to influence muscle tone and response. 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

Deeper muscles such as those involved in posture often are controlled from nuclei in the brain stem and basal ganglia. Posture or posturing may refer toIn humans Neutral spine or good posture Human position Abnormal posturing The brain stem (or brainstem) 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 Nervous system, afferent neurons --otherwise known as sensory or receptor Neurons -carry nerve impulses from receptors or sense 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. Muscle spindles are Sensory receptors within the belly of a Muscle, which primarily detect changes in the length of this muscle The sense of where our bodies are in space is called proprioception, the perception of body awareness. Senses are the physiological methods of Perception. The senses and their operation classification and theory are overlapping topics studied by a variety of fields Proprioception (ˌproʊpriːəˈsɛpʃən PRO -pree-o-SEP-shun from Latin proprius, meaning "one's own" and perception is the Sense 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.

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

Exercise is often recommended as a means of improving motor skills, fitness, muscle and bone strength, and joint function. A motor skill is generally agreed as a learned skill that involves voluntary movement to complete a task Physical fitness is used in two close meanings general fitness (a state of Health and well-being and specific fitness (a task-oriented definition based on the ability Exercise has several effects upon muscles, connective tissue, bone, and the nerves that stimulate the muscles. 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). The marathon is a long-distance foot race with an official distance of 42 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. Weightlifting, also called Olympic weightlifting or Olympic-style weightlifting, is a sport in which participants attempt a maximum weight single lift of a barbell 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. Neovascularization is the formation of functional microvascular networks with red blood cell perfusion 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. Pyruvic acid (CH3COCO2H is an alpha-keto acid. The Carboxylate Anion of pyruvic acid is known as pyruvate. The ability of the body to export lactic acid and use it as a source of energy depends on training level.

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. Rugby football (usually just " rugby " may refer to a number of sports through history descended from a common form of Football developed at Rugby School Boxing (sometimes also known as English boxing or pugilism) is a Combat sport in which two participants generally of similar weight,

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. Delayed onset muscle soreness (DOMS also sometimes called muscle fever, is the pain or discomfort often felt 24 to 72 hours after exercising and subsides generally within 2 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. A muscles contraction (also known as a muscle twitch or simply twitch) occurs when a Muscle fibre generates tension through the action of Actin Since lactic acid disperses fairly rapidly, it could not explain pain experienced days after exercise. ^[4]

Disease

Main article: Neuromuscular disease

Symptoms of muscle diseases may include weakness, spasticity, myoclonus and myalgia. Neuromuscular disease is a very broad term that encompasses many Diseases and ailments that either directly via intrinsic Muscle pathology or indirectly via Spasticity or muscular hypertonicity is a disorder of the body Motor system, and especially the central nervous system (CNS in which certain Muscles continually Myoclonus (maɪˈɒklənəs 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 Diagnostic procedures that may reveal muscular disorders include testing creatine kinase levels in the blood and electromyography (measuring electrical activity in muscles). Electromyography (EMG is a technique for evaluating and recording the activation signal of 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. 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 person's Ancestry. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Muscular dystrophy (MD 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. Neuromuscular disease is a very broad term that encompasses many Diseases and ailments that either directly via intrinsic Muscle pathology or indirectly via In general, problems with nervous control can cause spasticity or paralysis, depending on the location and nature of the problem. Paralysed redirects here For other uses see xx Paralysed (disambiguation Paralysis is the complete loss of Muscle function A large proportion of neurological disorders leads to problems with movement, ranging from cerebrovascular accident (stroke) and Parkinson's disease to Creutzfeldt-Jakob disease. A stroke is the rapidly developing loss of brain functions due to a disturbance in the blood vessels supplying blood to the brain Parkinson's disease (also known as Parkinson disease or PD) is a degenerative disorder of the Central nervous system that often impairs the sufferer's Creutzfeldt-Jakob disease ( CJD) is a very rare and incurable degenerative neurological disorder ( Brain Disease) that is ultimately

A non-invasive elastography technique that measures muscle noise is undergoing experimentation to provide a way of monitoring neuromuscular disease. Elastography is a non-invasive method in which stiffness or strain Images of Soft tissue are used to detect or classify Tumors. The sound produced by a muscle comes from the shortening of actomyosin filaments along the axis of the muscle. Myofibrils (obsolete term sarcostyles) are cylindrical Organelles found within Muscle cells They are bundles of actomyosin filaments In Biology, a filament is a long chain of Protein subunits such as those found in hair muscle or in Flagella. During contraction, the muscle shortens along its longitudinal axis and expands across the transverse axis, producing vibrations at the surface. The transverse or axial plane (also often transaxial plane) is an imaginary plane that divides the body into superior and inferior parts Vibration refers to mechanical Oscillations about an equilibrium point. ^[5]

Atrophy

There are many diseases and conditions which cause a decrease in muscle mass, known as muscle atrophy. Muscle atrophy is defined as a decrease in the mass of the muscle it can be a partial or complete wasting away of muscle Example include cancer and AIDS, which induce a body wasting syndrome called cachexia. Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled Cachexia (kəˈkɛksiə is loss of weight, Muscle atrophy, fatigue weakness and significant loss of appetite in someone who is not actively trying to Other syndromes or conditions which can induce skeletal muscle atrophy are congestive heart disease and some diseases of the liver. Heart failure is a Cardiac condition that occurs when a problem with the structure or function of the Heart impairs its ability to supply Liver diseases See also Chronic liver disease Viral hepatitis Acute Hepatitis A Acute Hepatitis B

During aging, there is a gradual decrease in the ability to maintain skeletal muscle function and mass, known as sarcopenia. Sarcopenia (from the Greek meaning "poverty of flesh" is the degenerative loss of Skeletal muscle mass and strength associated with Senescence. 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.

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 three to four daily episodes of muscle activity are responsible for the maintenance of muscle strength and responsiveness in bears during hibernation. ^[9]

Strength

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. Hypertrophy is the increase of the size of an organ or in a select area of the tissue 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 misleading 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. In human anatomy the masseter is one of the Muscles of mastication. The jaw is either of the two opposable structures forming or near the entrance to the Mouth. The 1992 Guinness Book of Records records the achievement of a bite strength of 4337 N (975 lbf) for 2 seconds. Guinness World Records, known until 2000 as The Guinness Book of Records (and in previous U The newton (symbol N) is the SI derived unit of Force, named after Isaac Newton in recognition of his work on Classical This article deals with the unit of force For the unit of mass see Pound (mass. 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. Skeletal muscle is a type of Striated muscle, which usually attaches to tendons 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. "Quads" redirects here For other uses see Quad The quadriceps femoris ( Latin for "four-headed of the femur" also The gluteus maximus' (or glutæus maximus) is the largest and most Superficial of the three Gluteal muscles.

• A shorter muscle will be stronger "pound for pound" (i. e. , by weight) than a longer muscle. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object 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. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain 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. A saccade is a fast movement of an eye, head or other part of an animal's body or device

• 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. The tongue is the large bundle of Skeletal muscles on the floor of the Mouth that manipulates Food for chewing and swallowing (deglutition 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. The heart is a muscular organ in all Vertebrates responsible for pumping Blood through the Blood vessels by repeated rhythmic Estimates of the power output of the human heart range from 1 to 5 watts. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. 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. "Quads" redirects here For other uses see Quad The quadriceps femoris ( Latin for "four-headed of the femur" also 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. The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity

Efficiency

The efficiency of human muscle has been measured (in the context of rowing and cycling) at 14% to 27%. In Physics, mechanical efficiency is the effectiveness of a machine and is defined as \text{Efficiency} = \frac{\text{Mechanical Advantage}}{\text{Velocity With regard to Watercraft, rowing is the act of propelling a boat using the motion of Oars in the water Cycling is the use of Bicycles or - less commonly - Unicycles Tricycles Quadricycles and other similar wheeled Human powered vehicles The efficiency is defined as the ratio of mechanical work output to the total metabolic cost. In Physics, mechanical work is the amount of Energy transferred by a Force. Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life.

Density of muscle tissue compared to adipose tissue

The density of mammalian skeletal muscle tissue is about 1. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different 06 kg/liter^[10]. This can be contrasted with the density of adipose tissue (fat), which is 0. "Adipose" redirects here For the Doctor Who monster see " Partners in Crime " 9196 kg/liter^[11]. This makes muscle tissue approximately 15% denser than fat tissue.

Muscle evolution

Evolutionarily, specialized forms of skeletal and cardiac muscles predated the divergence of the vertebrate/arthropod evolutionary line. The cardiac muscle is a type of involuntary striated Muscle found in the walls of the Heart. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes Arthropods are Animals belonging to the Phylum Arthropoda (from Greek ἄρθρον arthron, " Joint " ^[12] This indicates that these types of muscle developed in a common ancestor sometime before 700 million years ago (mya). An ancestor is a Parent or ( recursively) the parent of an ancestor (i In Astronomy, Geology, and Paleontology, mya or " mya " is an abbreviation for "million years ago". Vertebrate smooth muscle (smooth muscle found in humans) was found to have evolved independently from the skeletal and cardiac muscles.

See also

• Fascia
• Bodybuilding
• List of muscles of the human body
• Myopathy (pathology of muscle cells)
• Myotomy
• Rapid plant movement
• Atrophy
• Muscle atrophy
• Muscle tone (residual muscle tension)
• Electroactive polymers (materials that behave like muscles, used in robotics research)
• Muscle memory
• Musculoskeletal system
• Hand strength

Footnotes

References

• 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. Dr George B Johnson (born 11 June 1942, Newport News Virginia) is a science writer who wrote the weekly column "On Science" in the " Holt, Rinehart, and Winston. ISBN 0-03-016723-X

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.