A top-down view of skeletal muscle

Skeletal muscle is a type of striated muscle, usually attached to the skeleton. Skeletal muscles are used to create movement, by applying force to bones and joints; via contraction. They generally contract voluntarily (via somatic nerve stimulation), although they can contract involuntarily through reflexes. http://training. ... http://training. ... Image of sarcomere A sarcomere is the basic unit of a cross striated muscles myofibril. ... A top-down view of skeletal muscle Muscle (from Latin musculus little mouse [1]) is contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. ... For other uses, see Skeleton (disambiguation). ... In a general sense, locomotion simply means active movement or travel, applying not just to biological individuals. ... In physics, a net force acting on a body causes that body to accelerate; that is, to change its velocity. ... This article is about the skeletal organs. ... For other uses, see Joint (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. ... Nerves (yellow) Nerves redirects here. ... A reflex action is an automatic (involuntary) neuromuscular action elicited by a defined stimulus. ...

Muscle cells (also called fibers) have an elongated, cylindrical shape, and are multinucleated (in vertebrates and flies). The nuclei of these muscles are located in the peripheral aspect of the cell, just under the plasma membrane, which vacates the central part of the muscle fiber for myofibrils. (Conversely, when the nucleus is located in the center it is considered a pathologic condition known as centronuclear myopathy.) A right circular cylinder An elliptic cylinder In mathematics, a cylinder is a quadric surface, with the following equation in Cartesian coordinates: This equation is for an elliptic cylinder, a generalization of the ordinary, circular cylinder (a = b). ... Look up shape in Wiktionary, the free dictionary. ... Multinucleate (also multinucleated) cells have more than one nucleus per cell, which is the result of nuclear division not being followed by cytokinesis. ... HeLa cells stained for DNA with the Blue Hoechst dye. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... A simplified, global view of a neuromuscular junction: 1. ... A diagram of the structure of a Myofybril Myofibrils (obsolete term: sarcostyles) are cylindrical organelles, found within muscle cells. ... Note: Centronuclear myopathy includes Myotubular myopathy, as outlined below. ...

Skeletal muscles have one end (the "origin") attached to a bone closer to the centre of the body's axis and this is often but not always a relatively stationary bone (such as the scapula) and the other end (the "insertion") is attached across a joint to another bone further from the body's axis (such as the humerus). Contraction of the muscle causes the bones to rotate about the joint and the bones to move relative to one another (such as lifting of the upper arm in the case of the origin and insertion described here). Left scapula - front view () Left scapula - rear view () In anatomy, the scapula, or shoulder blade, is the bone that connects the humerus (arm bone) with the clavicle (collar bone). ... For other uses, see Joint (disambiguation). ... The humerus is a long bone in the arm or fore-legs (animals) that runs from the shoulder to the elbow. ...

There are several different ways to categorize the type of skeletal muscle. One method uses the type of protein contained in myosin (one of the important proteins that is responsible for the ability of muscle to contract). Using this classification scheme, there are two major types of fibers for skeletal muscles: Type I and Type II. Type I fibers appear reddish. They are good for endurance and are slow to tire because they use oxidative metabolism. Type II fibers are whitish; they are used for short bursts of speed and power, and use both oxidative metabolism and anaerobic metabolism depending on the particular sub-type, and are therefore quicker to tire. Cellular respiration is the process in which the chemical bonds of energy-rich molecules such as glucose are converted into energy usable for life processes. ... It has been suggested that this article or section be merged with Fermentation (food). ...

How skeletal muscle works

Main article: Muscle contraction

Bhuvnesh Bodybuilder demonstrating highly developed skeletal muscle.

The strength of skeletal muscle is directly proportional to its length and cross-sectional area. The strength of a joint, however, is determined by a number of biomechanical principles, including the distance between muscle insertions and pivot points and muscle size. Muscles are normally arranged in opposition so that as one group of muscles contract, another group 'relaxes' (in fact simply stretched) or lengthens. Antagonism in the transmission of nerve impulses (epsp and ipsp balance) to the muscles means that it is impossible to stimulate the contraction of two antagonistic muscles at any one time. During ballistic motions such as throwing, the antagonist muscles act to 'brake' the agonist muscles throughout the contraction, particularly at the end of the motion. In the example of throwing, the chest and front of the shoulder (anterior Deltoid) contract to pull the arm forward, while the muscles in the back and rear of the shoulder (posterior Deltoid) also contract and undergo eccentric contraction to slow the motion down to avoid injury. Part of the training process is learning to relax the antagonist muscles to increase the force output of the chest and anterior shoulder. 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. ... Image File history File linksMetadata No higher resolution available. ... Image File history File linksMetadata No higher resolution available. ... This article is about proportionality, the mathematical relation. ... Biomechanics is the research and analysis of the mechanics of living organisms or the application and derivation of engineering principles to and from biological systems. ... A top-down view of skeletal muscle Muscle (from Latin musculus little mouse [1]) is contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. ... Location The clavicular head of the pectoralis major takes its origin from the anterior surface of the medial half of the clavicle. ... In human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. ... Latissimus dorsi is a large flat muscle located on the back. ... 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. ...

Skeletal muscle cells are stimulated by acetylcholine, which is released at neuromuscular junctions by motor neurons.^[1] Once the cells are "excited", their sarcoplasmic reticulums will release ionic calcium (Ca²⁺), this interacts with the myofibrils and induces muscular contraction (via the sliding filament mechanism). Besides calcium, this process requires adenosine triphosphate (ATP). The ATP is produced by metabolizing creatine phosphate and glycogen within the muscle cells by mitochondria, as well by metabolizing glucose and fatty acids, obtained from blood and within the cell. Each motor neuron activates a group of muscle cells, and collectively the neurons and muscle cells are known as motor units. When more strength is required than can be obtained from a single motor unit, more units will be stimulated; this is known as motor unit recruitment. If more strength is required than can be obtained from the current degree of unit contraction, the motor neurons continue to recruit more motor units, and increase the frequency of neuronal firing. This results in tetanic contraction, which causes maximal muscular contraction. The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. ... A neuromuscular junction is the junction of the axon terminal of a motoneuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscles surface. ... In vertebrates, the term motor neuron (or motoneuron) classically applies to neurons located in the central nervous system (CNS) which project their axons outside the CNS and directly or indirectly control muscles. ... The endoplasmic reticulum or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport of proteins to be used in the cell membrane (e. ... This article is about the electrically charged particle. ... For other uses, see Calcium (disambiguation). ... The sliding filament mechanism is a process used by muscles to contract. ... Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer. ... Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ... Creatine, or creatine monohydrate [NH2-C(NH)-NCH2(COOH)-CH3], is a naturally occurring compound that helps to supply energy to the muscle cells. ... This article does not cite any references or sources. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. ... In chemistry, especially biochemistry, a fatty acid is a carboxylic acid often with a long unbranched aliphatic tail (chain), which is either saturated or unsaturated. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... A motor unit is a group of cells under the control of a single motor neuron; groups of motor units work together, as a single muscle. ... Physical strength is the ability of a person or animal to exert force on physical objects using muscles. ... Motor unit recruitment is the progressive activation of a muscle fibers motor units to accomplish increasing gradations of contractile strength. ... Tetanic contraction occurs when a motor unit has been maximally stimulated by its motor neuron. ...

Red and white fibers

Skeletal muscles contain two main types of fibers, which differ in the mechanism they use to produce ATP; the amount of each type of fiber varies from muscle to muscle and from person to person.

• Red ("slow-twitch") fibers have more mitochondria, store oxygen in myoglobin, rely on aerobic metabolism, have a greater capillary to volume ratio and are associated with endurance; these produce ATP more slowly. Marathon runners tend to have more red fibers, generally through a combination of genetics and training.
• White ("fast-twitch") fibers have fewer mitochondria, are capable of more powerful (but shorter) contractions, metabolize ATP more quickly, have a lower capillary to volume ratio, and are more likely to accumulate lactic acid. Weightlifters and sprinters tend to have more white fibers.

Fast fibers come in three varieties, called type IIa, IIx and IIb. Type IIx fibers in people used to be called, confusingly, type IIB. Type IIb fibers predominate in the fast muscle of small mammals that have to accelerate their limbs very fast against little load. Human type IIx (aka IIB) are our fastest fibers. Type IIa fibers are the slowest of all of them, and have only 36 units of myosin.^{[citation needed]} In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... An X-ray diffraction image for the protein myoglobin. ... This article or section should include material from aerobic respiration. ... This article does not cite any references or sources. ... Look up Endurance in Wiktionary, the free dictionary. ... Modern day marathon runners The word marathon refers to a long-distance road running event of 42. ... For the production of milk by mammals, see Lactation. ... This article is about the sport of weightlifting. ... Sprints are races where the runner tries to go as fast as humanly possible. ...

Characteristics of muscle types

Example of an unsaturated fat triglyceride. ... Phosphocreatine, also known as creatine phosphate or PCr, is a phosphorylated creatine molecule that is an important energy store in skeletal muscle. ... This article does not cite any references or sources. ...

Genes that define skeletal muscle phenotype

Skeletal muscle fiber-type phenotype in adult animals, and probably people, is regulated by several independent signaling pathways. These include pathways involved with the Ras/mitogen-activated protein kinase (MAPK), calcineurin, calcium/calmodulin-dependent protein kinase IV, and the peroxisome proliferator γ coactivator 1 (PGC-1). The Ras/MAPK signaling pathway links the motor neurons and signaling systems, coupling excitation and transcription regulation to promote the nerve-dependent induction of the slow program in regenerating muscle. Calcineurin, a Ca2+/calmodulin-activated phosphatase implicated in nerve activity-dependent fiber-type specification in skeletal muscle, directly controls the phosphorylation state of the transcription factor NFAT, allowing for its translocation to the nucleus and leading to the activation of slow-type muscle proteins in cooperation with myocyte enhancer factor 2 (MEF2) proteins and other regulatory proteins. Calcium-dependent Ca2+/calmodulin kinase activity is also upregulated by slow motor neuron activity, possibly because it amplifies the slow-type calcineurin-generated responses by promoting MEF2 transactivator functions and enhancing oxidative capacity through stimulation of mitochondrial biogenesis.

Contraction-induced changes in intracellular calcium or reactive oxygen species provide signals to diverse pathways that include the MAPKs, calcineurin and calcium/calmodulin-dependent protein kinase IV to activate transcription factors that regulate gene expression and enzyme activity in skeletal muscle.

Exercise-Included Signaling Pathways in Skeletal Muscle That Determine Specialized Characteristics of ST and FT Muscle Fibers

PGC1-α, a transcriptional coactivator of nuclear receptors important to the regulation of a number of mitochondrial genes involved in oxidative metabolism, directly interacts with MEF2 to synergistically activate selective ST muscle genes and also serves as a target for calcineurin signaling. A peroxisome proliferator-activated receptor δ (PPARδ)-mediated transcriptional pathway is involved in the regulation of the skeletal musclefiber phenotype. Mice that harbor an activated form of PPARd display an “endurance” phenotype, with a coordinated increase in oxidative enzymes and mitochondrial biogenesis and an increased proportion of ST fibers. Thus—through functional genomics—calcineurin, calmodulin-dependent kinase, PGC-1α, and activated PPARδ form the basis of a signaling network that controls skeletal muscle fiber-type transformation and metabolic profiles that protect against insulin resistance and obesity. Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ...

The transition from aerobic to anaerobic metabolism during intense work requires that several systems are rapidly activated to ensure a constant supply of ATP for the working muscles. These include a switch from fat-based to carbohydrate-based fuels, a redistribution of blood flow from nonworking to exercising muscles, and the removal of several of the byproducts of anaerobic metabolism, such as carbon dioxide and lactic acid. Some of these responses are governed by transcriptional control of the FT glycolytic phenotype. For example, skeletal muscle reprogramming from a ST glycolytic phenotype to a FT glycolytic phenotype involves the Six1/Eya1 complex, composed of members of the Six protein family. Moreover, the Hypoxia Inducible Factor-1α (HIF-1α) has been identified as a master regulator for the expression of genes involved in essential hypoxic responses that maintain ATP levels in cells. Ablation of HIF-1α in skeletal muscle was associated with an increase in the activity of bob-limiting enzymes of the mitochondria, indicating that the citric acid cycle and increased fatty acid oxidation may be compensating for decreased flow through the glycolytic pathway in these animals. However, hypoxia-mediated HIF-1α responses are also linked to the regulation of mitochondrial dysfunction through the formation of excessive reactive oxygen species in mitochondria.

Other pathways also influence adult muscle character. For example, physical force inside a muscle fiber may release the transcription factor Serum Response Factor (SRF) from the structural protein titin, leading to altered muscle growth.

External links

• Microscopic stains of skeletal and cardiac muscular fibers.

See also

• Myopathy
• Muscle atrophy

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. ... // Clinical settings of atrophy There are many diseases and conditions which cause a decrease in muscle mass, known as atrophy. ...

References

1. ^ Physiology, 2nd Ed., Saunders, 2002, ISBN 0-7216-9549-3, page 23.

Myoblasts are a type of stem cells that exist in muscles. ... Satellite cells are found in the mature muscle around the muscle fibres, and differentiate from myoblasts. ... The Sarcoplasm of a muscle fiber is comparable to the cytoplasm of other cells, but it houses unusually large amounts of glycosomes (granules of stored glycogen) and significant amounts of myoglobin, an oxygen binding protein. ... Muscle system The sarcolemma is the cell membrane of a muscle cell. ... The endoplasmic reticulum or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport of proteins to be used in the cell membrane (e. ... A T-tubule (or Transverse tubule), is a deep invagination of the plasma membrane found in skeletal and cardiac muscle cells. ... Cardiac muscle is a type of involuntary striated muscle found within the heart. ... Myocardium is the muscular tissue of the heart. ... An intercalated disc is an undulating double membrane separating adjacent cells in cardiac muscle fibers. ... Nebulette is an isoform of the protein nebulin. ... Cultured Smooth muscle of the aorta. ... oommen sir is a fool. ... Vascular smooth muscle refers to the particular type of smooth muscle found within, and composing the majority of the wall of blood vessels. ...