Afterhyperpolarization

Afterhyperpolarization (AHP) is a phase in the action potential of a neuron or muscle cell following the depolarization and repolarization phases. This phase is characterized by a transient increase in membrane potential that makes the cell more negative than its normal resting potential.

Overview

During an action potential, the membrane potential of the cell rapidly rises and falls. This is followed by a period of hyperpolarization, where the membrane potential is more negative than the resting potential. This is known as the afterhyperpolarization phase. The afterhyperpolarization phase is crucial in preventing the immediate generation of another action potential, thus ensuring that signals in neurons and muscle cells are transmitted in one direction only.

Mechanism

The afterhyperpolarization phase is primarily caused by the continued open state of potassium channels that were activated during the repolarization phase. This allows a greater amount of potassium ions to leave the cell, making the inside of the cell more negative.

There are three types of afterhyperpolarization: fast, medium, and slow. The fast afterhyperpolarization is primarily due to the efflux of potassium ions, while the medium and slow afterhyperpolarizations are due to the activation of other types of potassium channels.

Role in Neuronal Function

Afterhyperpolarization plays a crucial role in controlling the frequency of action potentials, and thus the overall excitability of neurons. It also plays a role in the adaptation of firing rates in response to sustained input, and in the regulation of spike timing.

Clinical Significance

Alterations in afterhyperpolarization have been implicated in a number of neurological and psychiatric disorders, including epilepsy, schizophrenia, and Alzheimer's disease. Understanding the mechanisms of afterhyperpolarization could therefore have important implications for the development of new treatments for these conditions.

The afterhyperpolarization phase is shown here in an action potential diagram.

See Also

• Action potential
• Hyperpolarization (biology)
• Depolarization
• Repolarization