neuronal action potential

Definition

Target type: biologicalprocess

An action potential that occurs in a neuron. [GOC:dph, GOC:isa_complete, GOC:tb]

Neuronal action potentials are rapid, transient changes in the electrical potential across the plasma membrane of a neuron, which serve as the primary means of communication in the nervous system. The process unfolds in a series of distinct stages:

1. **Resting potential:** In its resting state, a neuron maintains a negative electrical potential inside the cell relative to the outside. This is primarily due to an uneven distribution of ions across the membrane, with higher concentrations of potassium (K+) inside the cell and sodium (Na+) outside. The membrane is selectively permeable to K+, allowing it to leak out, contributing to the negative internal charge.

2. **Depolarization:** When a neuron receives a stimulus, it triggers the opening of voltage-gated sodium channels. This allows Na+ to rush into the cell, causing the internal charge to become more positive. If the stimulus is strong enough, the membrane potential reaches a critical threshold, initiating an action potential.

3. **Rising phase:** Once the threshold is reached, the influx of Na+ rapidly depolarizes the membrane, causing a steep increase in the electrical potential. The membrane potential approaches the equilibrium potential for Na+, which is positive.

4. **Peak:** The action potential reaches its maximum positive value, marking the peak of the depolarization phase. At this point, Na+ channels begin to inactivate, slowing the influx of Na+.

5. **Repolarization:** As Na+ channels inactivate, voltage-gated potassium channels open, allowing K+ to flow out of the cell. This outward movement of positive charge counteracts the influx of Na+, leading to a rapid decrease in the membrane potential, returning it towards its resting value.

6. **Hyperpolarization:** The potassium channels remain open for a brief period, leading to a temporary hyperpolarization of the membrane, where the potential becomes even more negative than the resting potential.

7. **Refractory period:** Following the action potential, the neuron enters a refractory period during which it is less likely to fire another action potential. This is due to the inactivation of Na+ channels and the increased permeability to K+. The refractory period ensures unidirectional propagation of the action potential and limits the frequency of firing.

8. **Return to resting potential:** The potassium channels eventually close, and the Na+/K+ pump actively restores the original ion concentration gradients, returning the neuron to its resting potential. This process is essential for maintaining the electrochemical gradient across the membrane and ensuring the ability to generate future action potentials.

The action potential is a self-regenerating event that propagates along the axon without losing its amplitude. This is achieved by the opening of voltage-gated ion channels at the leading edge of the action potential, triggering the depolarization of the adjacent membrane and initiating a new action potential. This continuous cycle ensures that the signal is transmitted efficiently over long distances within the nervous system.'
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Proteins (21)

Compounds (613)