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Both the extensor and flexor muscles are involved in the maintenance of a constant tone while at rest. In skeletal muscles, this helps maintain a normal posture. Resting muscle tone varies along a bell-shaped curve. Low tone is perceived as "lax, flabby, floppy, mushy, dead weight" and high tone is perceived as "tight, light, strong".
Spastic hypertonia involves uncontrollable muscle spasms, stiffening or straightening out of muscles, shock-like contractions of all or part of a group of muscles, and abnormal muscle tone. It is seen in disorders such as cerebral palsy, stroke, and spinal cord injury. Rigidity is a severe state of hypertonia where muscle resistance occurs ...
Hypotonia is a state of low muscle tone [1] (the amount of tension or resistance to stretch in a muscle), often involving reduced muscle strength. Hypotonia is not a specific medical disorder, but a potential manifestation of many different diseases and disorders that affect motor nerve control by the brain or muscle strength.
Muscle tone can also be due to tonic discharge of gamma motor neurons. The activation to these neurons are mostly from the descending fibers of the facilitatory reticular formation . [ 15 ] This leads to the stretching of muscle spindle, activation of alpha motor neurons and finally a partially contracted muscle.
Receptors in the muscles receive messages from the nervous system, which sense the amount of stretch in the muscle and sends that signal to the brain. The brain responds by sending a message back to reverse the stretch by contracting or shortening. [5] Characteristic features, analogy, and pathophysiology of common types of hypertonia.
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.
Dystonia is often intensified or exacerbated by physical activity, and symptoms may progress into adjacent muscles. [ 4 ] The disorder may be hereditary or caused by other factors such as birth-related or other physical trauma , infection , poisoning (e.g., lead poisoning ) or reaction to pharmaceutical drugs , particularly neuroleptics , [ 3 ...
[2] [3] The skeletal muscle cells are much longer than in the other types of muscle tissue, and are also known as muscle fibers. [4] The tissue of a skeletal muscle is striated – having a striped appearance due to the arrangement of the sarcomeres. A skeletal muscle contains multiple fascicles – bundles of muscle fibers.