hvíldarspennu

Hvíldarspenna, also known as resting potential, refers to the electrical potential difference across the plasma membrane of a cell when it is not stimulated or excited. This state is characteristic of excitable cells such as neurons and muscle cells. The resting potential is established and maintained by the differential distribution of ions across the cell membrane, primarily sodium (Na+), potassium (K+), chloride (Cl-), and negatively charged organic ions.

The sodium-potassium pump plays a crucial role in maintaining the resting potential by actively transporting three sodium ions out of the cell for every two potassium ions pumped into the cell. This creates concentration gradients for these ions. The selective permeability of the cell membrane to certain ions, particularly potassium ions through leak channels, allows potassium to diffuse down its concentration gradient and move out of the cell. This outward movement of positive charge contributes to a net negative charge inside the cell relative to the outside, thus establishing the resting potential, which is typically negative, often around -70 millivolts in neurons.

This polarized state is essential for the cell's ability to generate action potentials, which are rapid changes in membrane potential that enable communication in nerve cells and contraction in muscle cells. Any disruption or alteration of the ion gradients or membrane permeability can affect the resting potential and consequently the cell's excitability.