2. Action Potential
1. Depolarization
phase
2. Repolarization
phase
3. Hyperpolarization phase
Resting potential
Threshold potential
A rapid change in membrane
potential from –ve value to
+ve and then back to –ve
value due to transport of
ions across cell membrane,
resulting in generation of
impulse
3. Magnitude of stimulus
• Sub threshold stimulus
• Threshold stimulus
Minimum rise in RMP that can initiate action potential
-65mv (-70mv to -50mv)
4. Channels in Cell Membrane
1. K-Na leak channels leak towards conc: gradients
2. Voltage gated Na+ Channels remain closed at normal RMP
3. Voltage gated K+ Channels remain closed at normal RMP
4. Slow Ca- Na Channels only in Cardiac & Smooth muscles
5. Pumps in Cell Membrane
1. Na- K Electrogenic pump
2. Ca+ pump
15. Latent period
• The interval corresponds to the time it
takes the impulse to travel along the
axon from the site of stimulation to the
recording electrodes.
• Its duration depends upon
1. The distance between the stimulating
and recording electrodes
2. The speed of conduction.
16. "All-or-None" Law
• The action potential fails to occur if the stimulus is
subthreshold in magnitude, and it occurs with constant
amplitude and form regardless of the strength of the
stimulus if the stimulus is at or above threshold intensity.
17. Adaptation
• Slowly rising currents fail to fire the nerve because the
nerve adapts to the applied stimulus, a process called
adaptation.
18. Refractory Period
Period during which a second action potential can not occur in
presence of first action potential
1. Absolute Refractory Period Stimulus given during depolarization
Na channel become inactivated & can’t
be reopened
2. Relative Refractory Period Stimulus given during repolarization
Na channel have been reversed from state
of inactivation