Depolarization of neuronal plasma membrane

Question

How is the depolarization of neuronal plasma membrane produced? How does the cell return to its original rest?

Answer 1

When the neuron gets a stimulus by the binding of neurotransmitters to particular receptors sodium channels open and the permeability of plasma membrane in the postsynaptic region is changed. Sodium ions then go in the cell causing lowering (less negative) of membrane potential. If this reduction of membrane potential reaches a level called excitation threshold or threshold potential, about –50 mV, action potential is generated, that is, the depolarization intensifies till reaching its maximum level and depolarization current is transmitted along the remaining length of neuronal membrane.

If excitation threshold is reached voltage-dependent sodium channels in membrane open allowing more sodium ions to enter cell in favor of the concentration gradient and an estimated –35 mV level of positive polarization of the membrane is accomplished. The voltage-dependent sodium channels then close and more voltage dependent potassium channels open. Potassium ions then exit the cell in favor of the concentration gradient and the potential difference of the membrane diminishes, a process named as repolarization.

The action potential triggers the same electrical phenomenon in neighboring areas of plasma membrane and impulse is therefore transmitted from dendrites to terminal region of the axon.