jälkipotentiaali

Jälkipotentiaali, also known as afterpotential, is a term used in electrophysiology to describe the changes in membrane potential that occur after an action potential has been initiated. Following the rapid depolarization and repolarization phases of an action potential, the membrane potential often exhibits further, smaller fluctuations. These deviations are known as the afterpotential.

There are generally two types of afterpotentials: the positive afterpotential (PAP) and the negative afterpotential (NAP). The positive afterpotential is characterized by a brief period where the membrane potential becomes slightly more positive than the resting potential. This is often attributed to the slow closure of voltage-gated potassium channels or incomplete inactivation of sodium channels. The negative afterpotential, on the other hand, is a period where the membrane potential becomes hyperpolarized, meaning it is more negative than the resting potential. This hyperpolarization is typically caused by the continued outward movement of potassium ions through open potassium channels that close more slowly than sodium channels inactivate.

The presence and duration of these afterpotentials can vary depending on the type of neuron or muscle cell, as well as the specific ionic conductances involved. Afterpotentials play a role in regulating neuronal excitability and can influence the firing rate of neurons. They are a critical aspect of understanding the complex electrical behavior of excitable cells.