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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]
The origin of a muscle is the bone, typically proximal, which has greater mass and is more stable during a contraction than a muscle's insertion. [14] For example, with the latissimus dorsi muscle, the origin site is the torso, and the insertion is the arm. When this muscle contracts, normally the arm moves due to having less mass than the torso.
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]
The muscle performing an action is the agonist, while the muscle which contraction brings about an opposite action is the antagonist. For example, an extension of the lower arm is performed by the triceps as the agonist and the biceps as the antagonist (which contraction will perform flexion over the same joint).
The word myoclonus uses combining forms of myo-and clonus, indicating muscle contraction dysfunction. It is pronounced / ˌ m aɪ ˈ ɒ k l ə n ə s / [13] or / ˌ m aɪ ə ˈ k l oʊ n ə s, ˌ m aɪ oʊ-/ [14]. The prevalence of the variants shows division between American English and British English.
At the same time, signals travel up the spinal cord and cause contraction of the contralateral muscles of the hip and abdomen to shift the body’s center of gravity over the extended leg. To a large extent, the coordination of all these muscles and maintenance of equilibrium is mediated by the cerebellum and cerebral cortex. [5]
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]
Reciprocal inhibition is a neuromuscular process in which muscles on one side of a joint relax to allow the contraction of muscles on the opposite side, enabling smooth and coordinated movement. [1] This concept, introduced by Charles Sherrington, a pioneering neuroscientist, is also referred to as reflexive antagonism in some allied health fields.