tonus

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tonus

 [to´nus]
tone or tonicity; the slight, continuous contraction of a muscle, which in skeletal muscles aids in the maintenance of posture and in the return of blood to the heart.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

to·nic·i·ty

(tō-nis'i-tē),
1. A state of normal tension of the tissues by virtue of which the parts are kept in shape, alert, and ready to function in response to a suitable stimulus. In the case of muscle, it refers to a state of continuous activity or tension beyond that related to the physical properties; that is, it is active resistance to stretch; in skeletal muscle it is dependent upon the efferent innervation.
See also: isotonicity. Synonym(s): tonus
2. The osmotic pressure or tension of a solution, usually relative to that of blood.
See also: isotonicity.
[G. tonos, tone]
Farlex Partner Medical Dictionary © Farlex 2012

tonus

(tō′nəs)
n. pl. to·nuses
Body or muscular tone; tonicity.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.

to·nic·i·ty

(tō-nis'i-tē)
1. A state of normal tension of the tissues by virtue of which the parts are kept in shape, alert, and ready to function in response to a suitable stimulus. In the case of muscle, it refers to a state of continuous activity or tension beyond that related to the physical properties, i.e., its active resistance to stretch; in skeletal muscle, it is dependent on the efferent innervation.
Synonym(s): tonus.
2. The osmotic pressure or tension of a solution, usually relative to that of blood.
See also: isotonicity
[G. tonos, tone]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

tonus

the state of moderate contraction of muscle as a result of continuous low-level stimulation which maintains the posture of an animal.Tonus occurs because some cells in every muscle are in TETANUS (1) and the muscle feels firm. The condition continues without fatigue because some cells are relaxed whilst others are contracted.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005

tonus 

A state of partial contraction present in a muscle in its passive state as, for example, when the eye is in the physiological position of rest. Syn. muscle tone. See resting state of accommodation; physiological position of rest; tonic vergence.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann