Question

Can someone explain action potential generation followed by propagation.

Answer 1

Action potential generated when a stimulus applying is reaches to its threshold value. The resting membrane potential of neuron lies between -55 mV to -75 mV. When a stimulus reaches up to threshold value i.e. -55 mV an action potential generated. There are four phases of action potential:

1. Depolarization: At threshold stimulus value voltage gated sodium channel open and sodium ions rush into the cell as the extracellular concentration of sodium is very high.Since this sodium ions contain positive charge it brings depolarization in the cell and the membrane potential reaches up to + 55 mV.

2. Repolarization: Once the maximum depolarization is achieved, sodium ions closed and the change in membrane potential causes opening of potassium channel resulting into intracellular movement of potassium ions since potassium ion contain positive charge, outside movement brings repolarization in the nerve cell.

3. Hyperpolarization: Outside movement of potassium continues even after attaining the resting potential leading to hyperpolarization.

4. Attaining Resting potential: after hyperpolarization sodium channels open again and brings the membrane potential back to the resting potential.

Propagation: The action potential generated at the axon hillock and propagates as a wave through the axon. The currents flowing inwards at a point on the axon during an action potential spread out along the axon, resulting into depolarization of the the adjacent sections of its membrane. A sufficient strong depolarization causes a similar action potential at the neighboring membrane patches.