Action potential (AP)



Local potential Vs. Action potential

Local potential

Action potential
Subthreshold stimuli is enough to produce local potential

Threshold stimuli is needed

Gradual response

All or none response
Can be summated

Cannot be summated

Site of generation of action potential:

  • Motor neuron: Initial segment
  • Sensory neuron: Initial node of Ranvier

Events of an action potential:


  1. Neurons are LEAST excitable during Depolarization phase
  2. Maximum conductance of Na+: At the tip of depolarization (Point 4 in upper picture)
  3. Maximum conductance of K+: At mid point of repolarization (Point 5 of upper picture)
  4. Potential closest to equilibrium potential for K+: Point 1 of upper picture.

Refractory period

It is defined as a period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation.

Type From To
Absolute Firing level Repolarization is 1/3rd complete
Relative Repolarization is 1/3rd complete End of hyperpolarization

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