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MERP Physiology Mini 1 Learning objectives

Terms in this set (58)

The primary cation inside the cell is potassium which can cross the membrane through K-channels. The major anions are proteins, phosphates and sulfates all of which cannot cross the cell membrane.
Because there is a concentration gradient favoring K diffusion out of the cell, it moves down its concentration gradient leaving behind impermeable anions. This separation of charge makes the inside of the cell membrane slightly negative relative to the outside of the cell membrane. This electrical potential difference is called the resting membrane potential and is present in all cells of the body.
The number of K ions that move to generate the resting membrane potential is very small (~ 6x10-13 moles/cm2). Because of this there is not a measurable change in either the intracellular or extracellular K concentrations. This also means it would take a long time for the K concentration gradient to dissipate and cause the resting membrane potential to go to zero.
To sustain (maintain) the high intracellular K concentration, the Na-K ATPase pump moves two K ions into the cell in exchange for three Na ions out of the cell. Because more positive ions leave than enter the cell during this exchange, the pump is said to be "electrogenic". It makes the cell slightly more negative inside.
Do not confuse the role of K diffusion and the role of the Na-K ATPase pump in generating the resting membrane potential. The membrane potential is due to the diffusion of K from the cell. The pump just keeps intracellular K concentration high. Inhibiting the Na-K pump will only produce a small change (depolarization) in membrane potential. It will not prevent the membrane potential. The membrane potential will continue until the K concentrations are the same on both sides of the cell membrane.