Q. During the transmission of nerve Impulse through a nerve fibre, the potential on the inner side of the plasma membrane has which type of electric charge :-
(1) first positive, then negative and continue to be negative
(2) first negative, then positive and continue to be positive
(3) first positive, then negative and again back to positive
(4) first negative, then positive and again back to negative
Plasma membrane of a non-conducting neuron is positive on the outside and negative inside. The difference in charge is about 70 to 90 mV which is called as resting potential and the membrane is said to be polarized. A typical value of resting potential is -70mV.
When a plasma membrane of neuron is stimulated, its permeability changes and sodium potassium pump stop operating which results in the positive charge inside and negative charge outside.The nerve fibre is said to be in action potential or depolarized. The action potential inside the membrane is about +30 mV.
After a period of action potential, sodium pump operates again and membrane will get resting potential of -70mV by repolarization.
Thus, Option (4) first negative, then positive and again back to negative , is correct