Hvílaspennan

Hvílaspennan is an Icelandic term that translates to "rest voltage" or "resting potential" in English. It refers to the electrical potential difference across the plasma membrane of a cell when it is not actively stimulated. This potential difference is crucial for the proper functioning 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 and the selective permeability of the membrane to these ions. Primarily, the sodium-potassium pump actively transports sodium ions out of the cell and potassium ions into the cell, creating concentration gradients. The membrane is more permeable to potassium ions than to sodium ions at rest, due to the presence of potassium leak channels. This higher permeability allows potassium ions to diffuse out of the cell down their concentration gradient, leaving behind a net negative charge inside the cell relative to the outside.

The typical resting potential for most animal cells is around -70 millivolts (mV), although this value can vary depending on the cell type and specific physiological conditions. This negative charge inside the cell is essential for maintaining the cell's stability and readiness to respond to stimuli. When a stimulus arrives, changes in the permeability of the membrane to ions, particularly sodium, lead to a rapid change in the membrane potential, known as an action potential. This process is fundamental to nerve impulse transmission and muscle contraction.