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Muscle
system. Introduction
Muscle
contractile tissue found in animals, the function of which
is to produce motion.Muscle
is contractile tissue grouped into coordinated systems for
greater efficiency. In humans, the muscle systems are classified
by gross appearance and location of cells. The three types
of muscles are striated (or skeletal), cardiac, and smooth
(or nonstriated). Striated muscle is almost exclusively
attached to the skeleton and constitutes the bulk of the
body's muscle tissue. The multinucleated fibres are under
the control of the somatic nervous system and elicit movement
by forces exerted on the skeleton similar to levers and
pulleys. The rhythmic contraction of cardiac muscle is regulated
by the sinoatrial node, the heart's pacemaker. Although
cardiac muscle is specialized striated muscle consisting
of elongated cells with many centrally located nuclei, it
is not under voluntary control. Smooth muscle lines the
viscera, blood vessels, and dermis, and, like cardiac muscle,
its movements are operated by the autonomic nervous system
and thus are not under voluntary control. The nucleus of
eachshort, tapering cell is located centrally.
Unicellular
organisms, simple animals, and the motile cells of complex
animals do not have vast muscle systems. Rather, movement
in these organisms is elicited by hairlike extensions of
the cell membrane called cilia and flagella or by cytoplasmic
extensions called pseudopodia.
This
article consists of a comparative study of the muscle systems
of various animals, including an explanation of the process
of muscle contraction and an account of the human muscle
system as it relates to upright posture.
