MUSCLE FIBER

(Redirected from Myocytes)


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.
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.

Contents

Skeletal muscle fibers

Type I

Type II

Other terminology

See also

External links

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:

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

Type I

Type I muscle fibers (slow-oxidative fibers) use primarily cellular respiration and, as a result, have relatively high endurance.
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.)
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).

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.
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.
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.

See also

★ Myopathy, muscle pathology/diseases

★ myoblast

External links

★ http://www.coachr.org/fiber.htm - Article at coachr.org xplaining muscle fibers, especially in relation to training.

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