Myogenic contraction

Myogenic contraction refers to a contraction initiated by the myocyte cell itself instead of an outside occurrence or stimulus such as nerve innervation. Most often observed (although not necessarily restricted to) in smaller resistance arteries, this 'basal' tone may be useful in the regulation of organ blood flow and peripheral resistance, as it positions a vessel in a preconstricted state that allows other factors to induce additional constriction or dilation to increase or decrease blood flow.

Many cells have resting membrane potentials that are unstable. ility is usually due to ion channels in the cell membrane that spontaneously open and close (e.g. I_f channels in cardiac pacemaker cells). When the membrane potential reaches depolarization threshold an action potential (AP) is fired, excitation-contraction coupling initiates and the myocyte contracts.

Slow wave potential are unstable resting membrane potentials that continuously cycle through depolarization- and repolarization phases. However, not every cycle reaches depolarization threshold and thus an action potential (AP) will not always fire. Owing to temporal summation (depolarization potentials spaced closely together in time so that they summate), however, cell membrane depolarization will periodically reach depolarization threshold and an action potential will fire, triggering contraction of the myocyte.

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