24 Facts About Action potential


An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls.

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In muscle cells, for example, an action potential is the first step in the chain of events leading to contraction.

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At the axon hillock of a typical neuron, the resting Action potential is around –70 millivolts and the threshold Action potential is around –55 mV.

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Ion channels switch between conformations at unpredictable times: The membrane Action potential determines the rate of transitions and the probability per unit time of each type of transition.

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An action potential occurs when this positive feedback cycle proceeds explosively.

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The time and amplitude trajectory of the action potential are determined by the biophysical properties of the voltage-gated ion channels that produce it.

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Currents produced by the opening of voltage-gated channels in the course of an action potential are typically significantly larger than the initial stimulating current.

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Principal ions involved in an action potential are sodium and potassium cations; sodium ions enter the cell, and potassium ions leave, restoring equilibrium.

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How much the membrane Action potential of a neuron changes as the result of a current impulse is a function of the membrane input resistance.

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One consequence of the decreasing action potential duration is that the fidelity of the signal can be preserved in response to high frequency stimulation.

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Amplitude of an action potential is independent of the amount of current that produced it.

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Course of the action potential can be divided into five parts: the rising phase, the peak phase, the falling phase, the undershoot phase, and the refractory period.

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The undershoot, or afterhyperpolarization, phase is the period during which the membrane Action potential temporarily becomes more negatively charged than when at rest .

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The period during which no new action potential can be fired is called the absolute refractory period.

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Each action potential is followed by a refractory period, which can be divided into an absolute refractory period, during which it is impossible to evoke another action potential, and then a relative refractory period, during which a stronger-than-usual stimulus is required.

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Action potential generated at the axon hillock propagates as a wave along the axon.

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The currents flowing inwards at a point on the axon during an action potential spread out along the axon, and depolarize the adjacent sections of its membrane.

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Once an action potential has occurred at a patch of membrane, the membrane patch needs time to recover before it can fire again.

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However, only the unfired part of the axon can respond with an action potential; the part that has just fired is unresponsive until the action potential is safely out of range and cannot restimulate that part.

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The arrival of the action potential opens voltage-sensitive calcium channels in the presynaptic membrane; the influx of calcium causes vesicles filled with neurotransmitter to migrate to the cell's surface and release their contents into the synaptic cleft.

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Cardiac action potential plays an important role in coordinating the contraction of the heart.

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Whereas, the animal action potential is osmotically neutral because equal amounts of entering sodium and leaving potassium cancel each other osmotically.

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In 1902 and again in 1912, Julius Bernstein advanced the hypothesis that the action potential resulted from a change in the permeability of the axonal membrane to ions.

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In 1907, Louis Lapicque suggested that the action potential was generated as a threshold was crossed, what would be later shown as a product of the dynamical systems of ionic conductances.

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