Defining Membrane Potential
Membrane potential refers to the electrical voltage difference or charge separation across the plasma membrane of a cell. This difference arises due to the unequal distribution of electrically charged ions (like sodium, potassium, and chloride) between the inside and outside of the cell.
Creation and Maintenance
It is primarily established and maintained by ion pumps, notably the sodium-potassium pump, which actively transports ions against their concentration gradients, and by selective ion channels that allow specific ions to diffuse across the membrane. This creates a net negative charge inside the cell relative to the outside.
Resting Potential Example
In a resting neuron, the membrane potential, known as the resting potential (typically around -70 millivolts), is maintained by the sodium-potassium pump moving three sodium ions out for every two potassium ions moved in, coupled with potassium leak channels allowing K+ to slowly exit the cell.
Biological Significance
Membrane potential is fundamental for various cellular processes, including nerve impulse transmission (action potentials), muscle contraction, glandular secretion, and regulating heartbeat. It allows cells to respond to stimuli and transmit signals efficiently throughout an organism.