Action Potential

In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and endocrine cells, as well as in some plant cells. In neurons, they play a central role in cell-to-cell communication. In other types of cells, their main function is to activate intracellular processes. 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. 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 its "spike train". A neuron that emits an action potential is often said to "fire".

Action potentials are generated by special types of voltage-gated ion channels embedded in a cell's plasma membrane. These channels are shut when the membrane potential is near the resting potential of the cell, but they rapidly begin to open if the membrane potential increases to a precisely defined threshold value. When the channels open, they allow an inward flow of sodium ions, which changes the electrochemical gradient, which in turn produces a further rise in the membrane potential. This then causes more channels to open, producing a greater electric current, and so on. The process proceeds explosively until all of the available ion channels are open, resulting in a large upswing in the membrane potential. The rapid influx of sodium ions causes the polarity of the plasma membrane to reverse, and the ion channels then rapidly inactivate. As the sodium channels close, sodium ions can no longer enter the neuron, and they are actively transported out of the plasma membrane. Potassium channels are then activated, and there is an outward current of potassium ions, returning the electrochemical gradient to the resting state. After an action potential has occurred, there is a transient negative shift, called the afterhyperpolarization or refractory period, due to additional potassium currents. This is the mechanism that prevents an action potential from traveling back the way it just came.

In animal cells, there are two primary types of action potentials, one type generated by voltage-gated sodium channels, the other by voltage-gated calcium channels. Sodium-based action potentials usually last for under one millisecond, whereas calcium-based action potentials may last for 100 milliseconds or longer. In some types of neurons, slow calcium spikes provide the driving force for a long burst of rapidly emitted sodium spikes. In cardiac muscle cells, on the other hand, an initial fast sodium spike provides a "primer" to provoke the rapid onset of a calcium spike, which then produces muscle contraction.

Read more about Action Potential:  Biophysical Basis, Phases, Propagation, Taxonomic Distribution and Evolutionary Advantages, Experimental Methods, Neurotoxins, History, Quantitative Models

Other articles related to "action potential, potential, action":

Coincidence Detection In Neurobiology - Principles of Coincidence Detection
... If each input neuron's EPSP is subthreshold for an action potential at C, then C will not fire unless the two inputs from A and B are temporally close together ... of these two inputs may push the membrane potential of a target neuron over the threshold required to create an action potential ... drop significantly, preventing the membrane potential of the target neuron from reaching the action potential threshold ...
Afterhyperpolarization
... or AHP, describes the hyperpolarization phase of a neuron's action potential where the cell's membrane potential falls below the normal resting potential ... This is also commonly referred to as an action potential's undershoot phase ... in part causes the neuronal refractory period, the time period following an action potential during which a neuron cannot initiate a subsequent action ...
Action Potential - Quantitative Models
... models are essential for understanding the action potential, and offer predictions that may be tested against experimental data, providing a stringent test of a ... is the Hodgkin–Huxley model, which describes the action potential by a coupled set of four ordinary differential equations (ODEs) ... on larger and more integrated systems by joining action-potential models with models of other parts of the nervous system (such as dendrites and synapses), researches ...
Calcium Compounds - Nutrition
... sodium as the mineral that depolarizes the cell, proliferating the action potential ... In cardiac muscle, sodium influx commences an action potential, but during potassium efflux, the cardiac myocyte experiences calcium influx, prolonging the action ...
Sodium Channel - Voltage-gated - Gating
... Before an action potential occurs, the axonal membrane is at its normal resting potential, and Na+ channels are in their deactivated state, blocked on the ... In response to an electrical current (in this case, an action potential), the activation gates open, allowing positively-charged Na+ ions to flow into ... This increase in voltage constitutes the rising phase of an action potential ...

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