membranpotentialsförändringar

Membranpotential refers to the electrical potential difference that exists across the plasma membrane of a cell. This potential difference arises due to the unequal distribution of ions inside and outside the cell. The primary ions involved are sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl-).

The cell membrane is selectively permeable, meaning it allows certain ions to pass through more easily than others. This permeability is largely due to the presence of ion channels and pumps. The sodium-potassium pump, for example, actively transports three sodium ions out of the cell for every two potassium ions pumped into the cell, contributing significantly to the ion gradients.

In a resting cell, the membranpotential is typically negative on the inside relative to the outside. This is known as the resting membrane potential. The negative charge inside is primarily due to a higher concentration of negatively charged molecules within the cytoplasm, as well as the outward movement of positively charged potassium ions through leak channels.

Changes in membranpotential are crucial for cellular communication, particularly in excitable cells like neurons and muscle cells. When a cell is stimulated, ion channels open, allowing ions to flow across the membrane, altering the potential. This rapid change in membranpotential, called an action potential, allows for the transmission of electrical signals throughout the cell and between cells. The precise value of the membranpotential is determined by the Nernst equation and the Goldman-Hodgkin-Katz equation, which consider the concentrations and permeabilities of various ions.