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Tonic in physiology refers to a physiological response which is slow and may be graded. This term is typically used in opposition to a fast response. For instance, tonic muscles are contrasted by the more typical and much faster twitch muscles, while tonic sensory nerve endings are contrasted to the much faster phasic sensory nerve endings.
Tonic contractions are those contractions that are maintained from several minutes up to hours at a time. These occur in the sphincters of the tract, as well as in the anterior stomach. The other type of contractions, called phasic contractions, consist of brief periods of both relaxation and contraction, occurring in the posterior stomach and ...
In this way it conveys information about the duration of the stimulus. Some tonic receptors are permanently active and indicate a background level. Examples of such tonic receptors are pain receptors, joint capsule, and muscle spindle. [31] A phasic receptor is a sensory receptor that adapts
Phasic mechanoreceptors are useful in sensing such things as texture or vibrations, whereas tonic receptors are useful for temperature and proprioception among others. Slowly adapting: Slowly adapting mechanoreceptors include Merkel and Ruffini corpuscle end-organs , and some free nerve endings .
The contractile activity of smooth muscle cells can be tonic (sustained) or phasic (transient) [33] and is influenced by multiple inputs such as spontaneous electrical activity, neural and hormonal inputs, local changes in chemical composition, and stretch. [1]
Physiological differences in muscle fiber distribution—fast-twitch and slow-twitch muscle fibers, to be exact—play a role in exercise performance, and may make one person more inclined to ...
Tonic activity can be expressed in units of electrodermal level (EDL or SCL), while phasic activity is expressed in units of electrodermal responses (EDR or SCR). [23] Phasic changes (EDR) are short-lasting changes in EDA that appear as a response to a distinct stimulus. EDRs can also appear spontaneously without an observable external stimulus.
It can also include a polysynaptic component, as in the tonic stretch reflex. [3] When a muscle lengthens, the muscle spindle is stretched and its nerve activity increases. This increases alpha motor neuron activity, causing the muscle fibers to contract and thus resist the stretching. A secondary set of neurons also causes the opposing muscle ...