Despolarización

Despolarización refers to a rapid change in the electrical potential across a cell membrane, specifically a neuron or muscle cell. This change involves a decrease in the membrane potential, moving it closer to zero or even becoming positive. It is a crucial process for nerve impulse transmission and muscle contraction.

Typically, a cell membrane maintains a resting potential, which is a negative charge inside the cell relative to the outside. This resting potential is established by the unequal distribution of ions across the membrane, primarily sodium and potassium ions, and the action of ion pumps. When a stimulus, such as a neurotransmitter binding to a receptor, triggers the opening of ion channels, positively charged ions, most notably sodium ions, flow into the cell. This influx of positive charge reduces the negative charge inside the cell, causing the membrane potential to become less negative.

If the depolarization reaches a certain threshold level, known as the threshold potential, it triggers a much larger and faster depolarization called an action potential. The action potential is an all-or-nothing event that propagates along the axon of a neuron, enabling communication between cells. Following the action potential, the membrane repolarizes, returning to its resting potential, often with a brief hyperpolarization phase where the membrane potential becomes even more negative than resting.