muscle

(mŭs′ĕl )

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[L. musculus, diminutive of mus, mouse]
A type of tissue composed of contractile cells. Each muscle cell is filled with parallel actin and myosin filaments. When activated by an internal release of calcium, the filaments use the energy in adenosine triphosphate to crawl along each other in opposite directions. This movement shortens the length of the cell, which then contracts.
The three classes of myocytes (muscle cells) are skeletal (striated), cardiac (striated), and smooth; most human muscle is skeletal. A typical muscle has a central portion (the belly) and two or more attachment ends with tendons. The more stationary of the attachments is called the origin; the more movable attachment is called the insertion.



SELECTED MUSCLES OF THE BODY

MUSCLE FIBER





MORPHOLOGICAL FORMS OF MUSCLE

Comparison of Properties of Three Types of Muscle

	Smooth	Cardiac	Striated
Synonyms	Involuntary	Myocardial	Voluntary
	Nonstriated		Skeletal
	Visceral
Fibers
Length (in/m)	50-200		25,000
Thickness (in/m)	4-8		75
Shape	Spindles		Cylinders
Markings	No striation	Striation	Marked striation
Nuclei	Single	Single	Multiple
Effects of cutting related nerve	Slight	Regulation of heart rate is lost	Complete paralysis

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