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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 second paper, by Hugh Huxley and Jean Hanson, is titled "Changes in the cross-striations of muscle during contraction and stretch and their structural interpretation". It is more elaborate and was based on their study of rabbit muscle using phase contrast and electron microscopes. According to them: [19]
A stretch-shortening cycle (SSC) is an active stretch (eccentric contraction) of a muscle followed by an immediate shortening (concentric contraction) of that same muscle. Research studies [ edit ]
Since work is defined as force multiplied by displacement, the area of the graph shows the mechanical work output of the muscle. In a typical work-generating instance, the muscle shows a rapid curvilinear rise in force as it shortens, followed by a slower decline during or shortly before the muscle begins the lengthening phase of the cycle.
When muscle contraction is sufficiently great, it is able to stop the downward movement very quickly. This phase is sometimes called the phase of amortization in which the athlete absorbs some of the force and stops downward movement by the strong eccentric contraction of the muscles.
Tetanic contraction can exist in a variety of states, including isotonic and isometric forms—for example, lifting a heavy box off the floor is isotonic, but holding it at the elevated position is isometric. Isotonic contractions place muscles in a constant tension but the muscle length changes, while isometric contractions hold a constant ...
In muscle cells, for example, an action potential is the first step in the chain of events leading to contraction. In beta cells of the pancreas , they provoke release of insulin . [ a ] Action potentials in neurons are also known as " nerve impulses " or " spikes ", and the temporal sequence of action potentials generated by a neuron is called ...
Each muscle contraction involves an action potential that activates voltage sensors, and so releases Ca 2+ ions from the muscle fibre's sarcoplasmic reticulum. The action potentials that cause this also require ion changes: Na influxes during the depolarization phase and K effluxes for the repolarization phase.