Aksessioonipotentsiaal

Aksessioonipotentsiaal refers to the electrical potential difference across the plasma membrane of a neuron or muscle cell that allows it to generate an action potential. This potential is primarily determined by the concentration gradients of ions, such as sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl-), across the cell membrane, and the selective permeability of the membrane to these ions. At rest, a neuron maintains a negative resting membrane potential, typically around -70 millivolts, due to the unequal distribution of ions and the action of the sodium-potassium pump.

When a neuron receives a stimulus, it can cause a change in the membrane permeability, leading to an influx or efflux of ions. If the stimulus is strong enough to reach the threshold potential, usually around -55 millivolts, voltage-gated ion channels open. For an action potential, a rapid influx of sodium ions causes depolarization, making the inside of the cell positive relative to the outside. This is followed by repolarization, where potassium ions flow out of the cell, restoring the negative membrane potential. The ability of the cell membrane to undergo these rapid changes in potential is crucial for signal transmission in the nervous system and muscle contraction.