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Encyclopedia > Muscle fiber
A simplified, global view of a neuromuscular junction:1. Axon2. Neuromuscular junction3. Muscle fiber4. Myofibril
A simplified, global view of a neuromuscular junction:
1. Axon
2. Neuromuscular junction
3. Muscle fiber
4. Myofibril
A top-down view of skeletal muscle
A top-down view of skeletal muscle

A muscle fiber, also spelled muscle fibre (see spelling differences), also technically known as a myocyte, is a single cell of a muscle. Muscle fibers contain many myofibrils, the contractile unit of muscles. Muscle fibres are very long; a single fibre can reach a length of 30cm. Image File history File links Synapse_diag3. ... Image File history File links Synapse_diag3. ... An axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... 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. ... A diagram of the structure of a Myofybril Myofibrils (obsolete term: sarcostyles) are cylindrical organelles, found within muscle cells. ... http://training. ... http://training. ... American and British English spelling differences are one aspect of American and British English differences. ... 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. Cells in culture, stained for keratin (red) and DNA (green). ... 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. ... A diagram of the structure of a Myofybril Myofibrils (obsolete term: sarcostyles) are cylindrical organelles, found within muscle cells. ... A centimetre (American spelling centimeter, symbol cm) is a unit of length that is equal to one hundredth of a metre, the current SI base unit of length. ...


Muscle fibres can be grouped according to what kind of tissue they are found in -- skeletal muscle, smooth muscle, and cardiac muscle. The muscle cells of heart muscle tissue are called cardiomyocytes. Biological tissue is a collection of interconnected cells that perform a similar function within an organism. ... This article or section does not cite any references or sources. ... Cultured Smooth muscle of the aorta. ... Cardiac muscle is a type of involuntary striated muscle found within the heart. ...

Contents

Skeletal muscle fibers

Skeletal muscle fibers can be further divided into two basic types, type I (slow-twitch fibers) and type II (fast-twitch fibers). Type II is further divided, as follows: This article or section does not cite any references or sources. ...

type Type I Type IIa Type IIb
Description slow oxidative (SO) fibers fast oxidative-glycolytic (FOG) fast-twitch glycolytic fibers
myoglobin high medium low
mitochondria many moderate few
fatigues slowly moderate speed fast
color red ("dark meat") red white ("white meat")
diameter narrow medium wide

Glycolysis is a metabolic pathway by which a molecule of glucose (Glc) is oxidized to two molecules of pyruvic acid (Pyr). ... An X-ray diffraction image for the protein myoglobin. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ...

Type I

Type I muscle fibers (slow-oxidative fibers) use primarily cellular respiration and, as a result, have relatively high endurance. Cellular respiration describes the metabolism reactions and processes that take place in a cell to obtain biochemical energy from fuel molecules. ...


To support their high-oxidative metabolism, these muscle fibers typically have lots of mitochondria and myoglobin, and thus appear red (what is typically termed "dark" meat in poultry.) Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) (from Greek μιτος or mitos, thread + χονδριον or khondrion, granule) is a membrane-enclosed organelle, found in most eukaryotic cells. ... An X-ray diffraction image for the protein myoglobin. ... This article does not cite any references or sources. ...


Type I muscle fibers are typically found in muscles of animals that require endurance, such as chicken leg muscles or the wing muscles of migrating birds (e.g., geese). This article or section does not adequately cite its references or sources. ... Look up goose in Wiktionary, the free dictionary. ...


Type II

Type II muscle fibers use primarily anaerobic metabolism and have relatively low endurance. These muscle fibers are typically used during tasks requiring short bursts of strength, such as sprints or weightlifting. Type II muscle fibers cannot sustain contractions for significant lengths of time, and are typically found in the white meat (e.g., the breast) of chicken. This article or section does not cite any references or sources. ... Sprints are races where the runner tries to go as fast as humanly possible. ... A weightlifter about to jerk 180 kg[1] Weightlifting is a sport in which competitors attempt to lift heavy weights mounted on steel bars called barbells, the execution of which is a combination of power, flexibility, technique, mental and physical strength. ...


There are two sub-classes of type II muscle fibers, type IIa (Fast-Oxidative) and IIb (Fast-Glycolytic).

  • Type IIa (fast-oxidative) fibers also appear red, due to their high content of myoglobin and mitochondria.
  • Type IIb (fast-glycolytic) are the fastest firing and most powerful, twitching in upwards of 120 times per second, are the fiber type of choice to a power lifter. They also tire the fastest. These fibers appear white histologically, due to their low oxidative demand, manifested by the lack of myoglobulin and mitochondria (relative to the Type I and Type IIa fibers).

Other terminology

Most sources use the I/IIa/IIb division described above. However, this distinction is much more clear in other animals (such as chickens) than they are in humans, where the muscle tissue usually contains combinations of different kinds of fibers in varying proportions. This article or section does not adequately cite its references or sources. ...


Some terms used to describe this blending include:

  • "Type III" or "Intermediate fast-twitch fibers" are a cross between Type I and Type IIb. They can utilize both aerobic and anaerobic pathways for energy metabolism.
  • "Type IIc" fibers are created from a fusion of satellite cells to the corrupted Type IIb, so long as the cortisone hormone is inhibited, and offer the attributes of both Type IIa and Type IIb.

Cortisone (IPA:ˈkôrtəˌsōn) is a steroid hormone. ...

See also

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. ... Myoblasts are a type of stem cells that exist in muscles. ...

External links


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The differences in the speeds of contraction that gives the fibers their names can be explained, in part, by the rates of release of calcium by the sarcoplasmic reticulum (the muscle's storage site for calcium) and by the activity of the enzyme (myosin-ATPase) that breaks down ATP inside the myosin head of the contractile proteins.
Differences in muscle fiber com- position among athletes have raised the question of whether muscle structure is an acquired trait or is genetically determined.
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