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Muscle contractures can occur for many reasons, such as paralysis, muscular atrophy, and forms of muscular dystrophy. Fundamentally, the muscle and its tendons shorten, resulting in reduced flexibility. Various interventions can slow, stop, or even reverse muscle contractures, ranging from physical therapy to surgery.
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]
Hand contractures as seen in Freeman–Sheldon syndrome. In pathology, a contracture is a shortening of muscles, tendons, skin, and nearby soft tissues that causes the joints to shorten and become very stiff, preventing normal movement.
A fused tetanic contraction is the strongest single-unit twitch in contraction. [6] When tetanized, the contracting tension in the muscle remains constant in a steady state. This is the maximal possible contraction. [3] During tetanic contractions, muscles can shorten, lengthen or remain constant length. [7]
An impulse from a nerve cell causes calcium release and brings about a single, short muscle contraction called a muscle twitch. If there is a problem at the neuromuscular junction, a very prolonged contraction may occur, such as the muscle contractions that result from tetanus. Also, a loss of function at the junction can produce paralysis. [5]
A cramp is a sudden, involuntary, painful skeletal muscle contraction [1] [2] or overshortening associated with electrical activity; [3] while generally temporary and non-damaging, they can cause significant pain and a paralysis-like immobility of the affected muscle.
The activation of more motor neurons will result in more muscle fibers being activated, and therefore a stronger muscle contraction. Motor unit recruitment is a measure of how many motor neurons are activated in a particular muscle, and therefore is a measure of how many muscle fibers of that muscle are activated.
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]