Myogenic
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187516368
2008-01-28T18:41:56Z
146.9.22.121
'''Myogenic''' contraction refers to a [[myocyte]] [[contraction]] that originates from a property of the [[myocyte]] itself. I.e. the contraction is initiated by the cell itself, not an outside occurrence or stimulus such as nerve innervation.
== Mechanisms ==
=== Unstable Membrane Potentials ===
Many [[cells]] have [[resting membrane potential]]s that are unstable. This instability is usually due to [[ion channels]] in the [[cell membrane]] that spontaneously open and close (e.g. [[Funny current|I<sub>f</sub> channels]] in [[cardiac pacemaker]] cells). When the [[membrane potential]] reaches [[Action_potential#Threshold_and_initiation|depolarization threshold]] an [[action potential]] (AP) is fired, [[excitation-contraction coupling]] initiates and the [[myocyte]] contracts.
==== Slow wave potentials ====
[[Slow wave potential]] are unstable [[resting membrane potential]]s that continuously cycle through [[depolarization]]- and [[repolarization]] phases. However, not every cycle reaches [[Action_potential#Threshold_and_initiation|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 [[Action_potential#Threshold_and_initiation|depolarization threshold]] and an [[action potential]] will fire, triggering contraction of the [[myocyte]].
==== Pacemaker potentials ====
[[pacemaker potential|Pacemaker potential]]s are unstable [[resting membrane potential|cell membrane potentials]] that reach [[Action_potential#Threshold_and_initiation|depolarization threshold]] with every [[depolarization]]/[[repolarization]] cycle. This results in [[action potential|AP's]] being fired according to a set rhythm. [[cardiac pacemaker|Cardiac pacemaker]] cells, a type of [[cardiac myocyte]] in the [[SA node]] of heart, are an example of cells with a [[pacemaker potential]].
=== Stretch ===
This mechanism involves the opening of mechanically-gated Ca<sup>2+</sup> channels when some [[myocyte]]s are stretched. The resulting influx of Ca<sup>2+</sup> ions lead to the initiation of [[excitation-contraction coupling]] and thus [[contraction]] of the myocyte.
== See also ==
[[Membrane potential]] <br />
[[Action potential]] <br />
[[Excitation-contraction coupling]]<br />
[[Myogenic mechanism]] (Myogenic reflex) <br />
[[Category:Animal physiology]]