involuntary muscle (smooth muscle) Muscle whose activity is not under the control of the will; it is supplied by the autonomic nervous system. Involuntary muscle comprises long spindle-shaped cells without striations. These cells occur singly, in groups, or as sheets in the skin, around hair follicles, and in the digestive tract, respiratory tract, urinogenital tract, and the circulatory system. The cells contract slowly in spontaneous rhythms or when stretched; they may show sustained contraction (tonus) for long periods without fatigue. Compare voluntary muscle.
involuntary muscle One of three types of muscle in the body, so called because, unlike skeletal muscle, it is not under the conscious control of the brain but stimulated by the autonomic nervous system and by hormones. Smooth muscle is the muscle of the alimentary canal, blood vessels, and bladder. Cardiac muscle powers the heart.
More From encyclopedia.com
Cell Plate , Skip to main content cell plate Mast Cell , Skip to main content mast cell Companion Cell , Skip to main content companion cell Schwann Cell , Schwann cell (neurilemma cell) A cell that forms the myelin sheath of a nerve fibre. Each cell is responsible for a single length of the fibre (calle… Adherens Junction , adherens junction A cell junction that is commonly observed in epithelial (see EPITHELIUM) cells (e.g. those lining the intestine and those in cardia… Cell Membrane , cell membrane (plasmalemma, plasma membrane, protoplast) A sheet-like membrane, 7.5–10 nm thick, that forms a selectively permeable barrier enclosing…
About this article
All Sources -
Updated Aug 08 2016 About encyclopedia.com content Print Topic
You Might Also Like