Q. How is the depolarization of the neuronal plasma membrane generated? How does the cell return to its original rest?
When the neuron receives a stimulus by the permeability of the plasma membrane in the postsynaptic region is altered and the binding of neurotransmitters to specific receptors sodium channels open. Sodium ions then go into the cell causing lowering that is less negative of the membrane potential. If this reduction of the membrane potential reaches a level called as the excitation threshold or threshold potential about -50 mV the action potential is generated that is the depolarization intensifies until reaching its maximum level and the depolarization current is transmitted along the remaining length of the neuronal membrane.
If the excitation threshold is reached voltage-dependent sodium channels in the membrane open allowing more sodium ions to enter the cell in favor of the concentration gradient and an approximate -35 mV level of positive polarization of the membrane is achieved and 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 decreases a process called as repolarization.
The action potential triggers the same electrical phenomenon in neighboring regions of the impulse and the plasma membrane is thus transmitted from the dendrites to the terminal region of the axon.