Skeletal muscle fiber types

Table 11.1 Features of Skeletal Muscle Fiber Types...

Mackle, B. G. and Terjung, R. L. (1983) Blood flow to different skeletal muscle fiber types during contraction. Am. J. 

Skeletal muscle fiber type is determined by innervation. 

Schiaffino S, Reggiani C (1996) Molecular diversity of myofibrillar proteins gene regulation and functional significance. Physiol Rev 76 371-423 Pette D, Staron RS (1997) Mammalian skeletal muscle fiber type transitions. Into... 

Muscle tissue is unique in its ability to shorten or contract. The human body has three basic types of muscle tissue histologically classified into smooth, striated, and cardiac muscle tissues. Only the striated muscle tissue is found in all skeletal muscles. The type of cells which compose the muscle tissue are known as contractile cells. They originate from mesenchymal cells which differentiate into myoblasts. Myoblasts are embryonic cells which later differentiate into contractile fiber cells. 

Zebrafish larvae possess two types of skeletal muscle fibers. Slow (red) muscle fibers, a superficial monolayer on the siuface of the myotome, are equipped for oxidative phosphorylation, can generate relatively large stores of energy, and are most resistant to fatigue. Fast (white) muscle fibers, in the deep portion of the myotome, are least resistant to fatigue because they rely on anaerobic glycolysis for... 

Papadopoulos, S., K.D. Jurgens, and G. Gros (2000). Protein diffusion in living skeletal muscle fibers dependence on protein size, fiber type, and contraction. Biophys. J. 79 2084-2094. 

Skeletal muscles are organized into extrafusal and intrafusal fibers. Extrafusal fibers are the strong, outer layers of muscle. This type of muscle fiber is the most common. Intrafusal fibers, which make up the central region of the muscle, are weaker than extrafusal fibers. Skeletal muscles fibers are additionally characterized as fast or slow based on their activity patterns. Fast, also called white, muscle fibers contract rapidly, have poor blood supply, operate anaerobically, and fatigue rapidly. Slow, also called red, muscle fibers contract more slowly, have better blood supplies, operate aerobically, and do not fatigue as easily. Slow muscle fibers are used in movements that are sustained, such as maintaining posture. 

Martin WH 3rd, Murphree SS, Saffitz JE. [i-Adrenergic receptor distribution among muscle fiber types and resistance arterioles of white, red, and intermediate skeletal muscle. Circ Res 1989 64 1096-1105. 

Muscle cells contain many mitochondria which are often present as reticulum-like structures extending longitudinally in the fiber near the sarcolemma, rather than as discrete ellipsoidal organelles found in many other cells. These provide much of the high-energy phosphate needed to power contraction and to operate the Ca + pumps that control the cytosolic calcium concentration. Different types of skeletal muscle fibers differ considerably in the extent and organization of both their SR and mitochondria. 

As a prerequisite for fine motor control, skeletal muscle fibers are electrically isolated from one another, and, accordingly, do not express either connexin-43 (the major gap junction protein) or N-cadherin (the major adherens protein in cardiac intercalated discs). Asynchronous islands of intramyocardial skeletal muscle can result in lethal arrhythmias in mice [21]. Although cell types such as fetal cardiomyocytes [22] and cardiomyocytes derived from murine or human embryonic stem cells [23] are capable of electromechanical coupling, their clinical use has unfortunately been hampered by technical, ethical, moral, social and legal hurdles. 

Although skeletal muscle fibers, particularly of the "fast glycolytic" type, are able to utilize their phospho-creatine (PCr) and glycogen stores for sizable bursts of energy turnover at rates well exceeding that of oxidative recovery processes, these stores are small in... 

The spear-type glass microelectrode (Hinke-type) (2) (Figure la) has been used to determine the intracellular pH of the crab muscle fibers (3,4), cytoplasm of the giant squid axon (5), rat sartorius muscle fibers (6), rat atrial muscle fibers (7), vacuole of the algae Nitella flexilis (8), rat kidney tubular fluid (9,10), nerve cells of mollusk ganglia (11), and skeletal muscle fibers of the rat (4,12,13,14). 

Muscle spindles are intrafusal mechanoreceptors that are widely distributed within skeletal muscle fibers in the belly of the muscle. They exist in parallel with the much larger extrafusal skeletal muscle fibers, and the cotmective tissue around the muscle spindles is continuous with the connective tissue around the other muscle fibers. The muscle spindles mediate a response to a load placed on the muscle this is known as the load reflex. Muscle spindles have a dampening function, as well. They prevent some types of oscillation and jerkiness in body movement. In fact, tremors noted, especially during times of extreme anxiety or stimulation, represent a failure to dampen this response smoothly. In addition to serving at a subconscious level, the muscle spindle reflex is invoked in voluntary motor activity. 

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