Resting membrane potential - electrical polarity and maintenance requirements

• A resting membrane potential exists when there is a buildup of: 1. positive ions outside the membrane. 2. negative ions inside the membrane. • Membranes with opposing charges are said to be polarized. • The difference in charge applies only to the small distance across the membrane. • The cytosol and extracellular fluids are electrically neutral. • A typical value for a resting membrane potential is -70 millivolts. • Maintaining a resting membrane potential requires. 1. An unequal distribution of ions and charges. 2. A greater permeability of the membrane to K+ ions than Na+ ions because of more K+ pores in the membrane. • More K+ ions diffuse out than Na+ ions diffuse in leaving the interior of the cell slightly negative. 3.The Na+/K+ pump's effect. • Since Na+ is always leaking in and K+ leaking out, the pump maintains the diffusion gradients of these ions by pumping out the Na+ as fast as it leaks in. • A constantly maintained electrical charge - or resting membrane potential - results. • In summary, • Many K+ ions leak out of the cell leaving the inside of the membrane slightly negative. • A small amount of Na+ ions leak into the cell. • The Na+/K+ pump maintains the chemical gradients of Na+ and K+ and provides a small change in voltage. • The average voltage maintained across a resting neuron's cell membrane is about -70 mV.

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