involuntary muscle

Medical Dictionary

involuntary muscle n.
Any of the smooth muscles, except for the cardiac muscle, not under control of the will.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Encyclopedia Britannica
Encyclopedia

involuntary muscle

muscle that shows no cross stripes under microscopic magnification. It consists of narrow spindle-shaped cells with a single, centrally located nucleus. Smooth muscle tissue, unlike striated muscle, contracts slowly and automatically. It constitutes much of the musculature of internal organs and the digestive system.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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