The Sodium-Potassium Pump (Na-K Pump) was discovered in
the 1950’s by Skou, who won the Nobel Prize in 1997. It is the mechanism used by the
cell to preserve a high intracellular concentration of Potassium and low concentration
of Sodium, compared to opposite concentrations in the extracellular fluid. The cell
membrane has a protein channel that uses ATP energy to create the Na-K gradients for
cell function. The channel has an affinity for sodium ions. When they enter the
channel the protein changes shape, allowing potassium to move against gradient. The
process is reversible.
Highly excitable cells such as
neurons are able to respond to stimuli and transmit impulses, and the Na-K Pump is
needed for this activity. Neurons preserve their membrane potential by creating high
intracellular potassium and low sodium.
The Na-K Pump
resets the neuron to its resting potential after an action potential has been
transmitted. Thus, it is not the Na-K Pump that transmits the signal, but instead it
resets the cell membrane to allow it to transmit another action potential. The
electrical impulse of the action potential triggers the release of neurotransmitter at
the synaptic gap. It is the neurotransmitter, which crosses the gap and fires the
second neuron.
The Na-K Pump maintains a nerve in a
polarized state (also called resting potential), ready to be triggered by an Action
Potential. With passage of the Action Potential there is a sudden depolarization of the
neuron, causing opening of voltage-activated channel at which point the Na-K Pump
reverses and resets the membrane to resting potential, ready for the next Action
Potential. During the reset process the neuron is in a refractory
period.
Thus, the Na-K Pump sets and resets the cell
membrane to allow it to transmit the Action Potential. The Action Potential causes the
release of the neurotransmitter, which passes the signal to the next
nerve.
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