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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.
Depiction of smooth muscle contraction. Muscle contraction is the activation of tension-generating sites within muscle cells. [1] [2] In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscle length, such as when holding something heavy in the same position. [1]
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 ...
Smooth muscle may contract phasically with rapid contraction and relaxation, or tonically with slow and sustained contraction. The reproductive, digestive, respiratory, and urinary tracts, skin, eye, and vasculature all contain this tonic muscle type.
A spasm is a sudden involuntary contraction of a muscle, [1] a group of muscles, or a hollow organ, such as the bladder. A spasmodic muscle contraction may be caused by many medical conditions, including dystonia. Most commonly, it is a muscle cramp which is accompanied by a sudden burst of pain. A muscle cramp is usually harmless and ceases ...
In physiology, medicine, and anatomy, muscle tone (residual muscle tension or tonus) is the continuous and passive partial contraction of the muscles, or the muscle's resistance to passive stretch during resting state. [1] [2] It helps to maintain posture and declines during REM sleep. [3]
This muscle is in a state of tonic contraction, but during defecation, it relaxes to allow the release of feces. Movement of the feces is also controlled by the involuntarily controlled internal anal sphincter, which is an extension of the circular muscle surrounding the anal canal. It relaxes to expel feces from the rectum and anal canal.
The Ib sensory feedback generates stretch reflexes and supraspinal responses which control muscle contraction. Ib afferents synapse with interneurons in the spinal cord that also project to the brain cerebellum and cerebral cortex. The Golgi tendon reflex assists in regulating muscle contraction force. It is associated with the Ib.