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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]
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]
A myoclonic seizure (myo "muscle", clonic "jerk") is a sudden involuntary contraction of muscle groups. The muscle jerks consist of symmetric, mostly generalized jerks, localized in the arms and in the shoulders and also simultaneously with a head nod; both the arms may fling out together and simultaneously a head nod may occur.
The smooth muscle of the blood vessels reacts to the stretching of the muscle by opening ion channels, which cause the muscle to depolarize, leading to muscle contraction. This significantly reduces the volume of blood able to pass through the lumen, which reduces blood flow through the blood vessel.
Muscle stiffness and contraction can cause abnormal resting postures. Around 70% of those with SPS have the "classic" form of the disease. [5] People with classic SPS typically first experience intermittent tightness or aching in the muscles of the trunk. [6] These muscles repeatedly and involuntarily contract, causing them to grow and rigidify ...
An isometric exercise is an exercise involving the static contraction of a muscle without any visible movement in the angle of the joint. The term "isometric" combines the Greek words isos (equal) and -metria (measuring), meaning that in these exercises the length of the muscle and the angle of the joint do not change, though contraction ...
Fasciculations arise as a result of spontaneous depolarization of a lower motor neuron leading to the synchronous contraction of all the skeletal muscle fibers within a single motor unit. An example of normal spontaneous depolarization is the constant contractions of cardiac muscle, causing the heart to beat. Usually, intentional movement of ...
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.