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Muscle that is not controlled by individual volition, including smooth muscle and cardiac muscle.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
involuntary muscleSmooth muscle, usually within an organ or blood vessel, that contracts under the influence of unconscious processes mediated by the AUTONOMIC nervous system rather than by the conscious will.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
smooth musclea type of muscle called ‘involuntary’ because it is innervated by the AUTONOMIC NERVOUS SYSTEM. It is also called ‘visceral’ as it is found in the alimentary canal, the blood vessels, CILIARY BODY, respiratory passages and URINOGENITAL SYSTEM. It is also called ‘smooth’ since the MYOFIBRILS lack striations. Involuntary muscle contracts slowly and takes a long time to fatigue. Compare STRIATED MUSCLE.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005