20 Facts About Action potentials

Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and in some plant cells.

Action potentials are generated by special types of voltage-gated ion channels embedded in a cell's plasma membrane.

Action potentials are driven by channel proteins whose configuration switches between closed and open states as a function of the voltage difference between the interior and exterior of the cell.

Action potentials are triggered when enough depolarization accumulates to bring the membrane potential up to threshold.

The frequency at which a neuron elicits action potentials is often referred to as a firing rate or neural firing rate.

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In contrast to passive spread of electric potentials, action potentials are generated anew along excitable stretches of membrane and propagate without decay.

Action potentials are most commonly initiated by excitatory postsynaptic potentials from a presynaptic neuron.

Rectifying channels ensure that action potentials move only in one direction through an electrical synapse.

Therefore, action potentials are said to be all-or-none signals, since either they occur fully or they do not occur at all.

The period during which action potentials are unusually difficult to evoke is called the relative refractory period.

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

However, if a laboratory axon is stimulated in its middle, both halves of the axon are "fresh", i e, unfired; then two action potentials will be generated, one traveling towards the axon hillock and the other traveling towards the synaptic knobs.

For example, action potentials move at roughly the same speed in a myelinated frog axon and an unmyelinated squid giant axon, but the frog axon has a roughly 30-fold smaller diameter and 1000-fold smaller cross-sectional area.

In general, action potentials that reach the synaptic knobs cause a neurotransmitter to be released into the synaptic cleft.

Muscle action potentials are provoked by the arrival of a pre-synaptic neuronal action potential at the neuromuscular junction, which is a common target for neurotoxins.

The fundamental difference from animal action potentials is that the depolarization in plant cells is not accomplished by an uptake of positive sodium ions, but by release of negative chloride ions.

Action potentials are found throughout multicellular organisms, including plants, invertebrates such as insects, and vertebrates such as reptiles and mammals.

The integration of various dendritic signals at the axon hillock and its thresholding to form a complex train of action potentials is another form of computation, one that has been exploited biologically to form central pattern generators and mimicked in artificial neural networks.

Study of action potentials has required the development of new experimental methods.

The conduction velocity of action potentials was first measured in 1850 by du Bois-Reymond's friend, Hermann von Helmholtz.