Describe Action Potential

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 stereotyped trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and endocrine 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.[citation needed] 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".


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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 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 electrical current, which produces a further rise in the membrane potential. This then causes more channels to open, producing a greater electrical current, etc. The process proceeds explosively until all of the available ion channels are open, resulting in a large upswing in the membrane potential, often to the extent of briefly reversing its polarity. The ion channels then rapidly inactivate, allowing the membrane potential to drop back to its baseline level, sometimes sped by other types of voltage-gated ion channels that are active specifically during the falling phase of an action potential. Having problem with Displacement Equation keep reading my upcoming posts, i will try to help you.

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 less than 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.