Depolarization of neuronal plasma membrane

Question

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

Answer 1

Whenever the neuron obtains a stimulus by the binding of neurotransmitters to particular receptors sodium channels open and the permeability of plasma membrane in the postsynaptic area is modified. Sodium ions then go to the cell causing lowering (that is, less negative) of the membrane potential. Whenever this reduction of membrane potential reaches a level termed as the excitation threshold, or threshold potential, around –50 mV, the action potential is produced, that is, the depolarization intensifies until reaching its utmost level and the depolarization current is transmitted all along the remaining length of neuronal membrane.

When the excitation threshold is reached voltage-dependent sodium channels in membrane open permitting more sodium ions to enter the cell in the favor of concentration gradient and an around –35 mV level of positive polarization of the membrane is attained. The voltage-dependent sodium channels then close and additional voltage-dependent potassium channels open. Potassium ions then depart the cell in favor of concentration gradient and the potential difference of the membrane reduces, a process termed as repolarization.

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