Potential difference across the nerve fibre during conduction of impulses

1. ACTION POTENTIAL

2. • Action potential is abrupt pulse like change in
the membrane potential lasting for a fraction of
second
• During action potential there is reversal of
membrane potential i.e. inside becomes positive
and outside becomes Negative.
• We can see the action potential on cathode ray
oscilloscope

3. Properties of Action Potential
• Abrupt or sudden in onset
• Have limited magnitude or amplitude i.e. Inside, the
potential will go to + 35 or + 45 mV and not beyond
that.
• It is of short duration. Duration is in milli seconds.
Duration of spike potential Is 1 -2 milli second.
Action potential with plateau has longer duration i.e.
may be upto 300 msec

4. Properties of Action Potential
• It obeys All or None law i.e. if stimulus is sub
threshold it is not produced and when the stimulus
is threshold or supra threshold it will be produced
with maximum amplitude.
• It is self propagated i.e. once produced in a
membrane it is automatically propagated in both
directions. Inside the body because of presence of
synapses it is transmitted in one direction i.e. from
pre synaptic to post synaptic.
• It is not decremented with distance i.e. it will travel
with same amplitude through all the distance.

5. Properties of Action Potential
• It has refractory period. The period during which the
tissue will not respond to second stimulus after the
application of first stimulus. It could be Absolute
and Refractory.
▫ Absolute no response of tissue what so ever may be the
strength of stimulus
▫ Relative response with higher stimulus than threshold
stimulus

6. Phases of Action Potential
• DEPOLARIZATION: Sudden loss of Negativity
inside the membrane is depolarization.
• REPOLARIZATION: return of negativity inside
the membrane is Repolarization.
▫ After Depolarization
• HYPERPOLARIZATION: More Negativity inside
• RESTING MEMBRANE POTENTIAL

9. Mechanism of Action Potential
• Understanding of
▫ Channels Involved
 Voltage gated Sodium Channels
 Voltage gated Potassium Channels
 Sodium Potassium ATPase Pump
▫ Movements of ions
 Concentrations of Sodium and Potassium in ECF
and ICF
 Direction of movement

10. Voltage Gated Sodium Channels
• Two gates: outer side activation gate, inner side
inactivation gate
• In resting state activation gate is closed and
inactivation gate is open

11. Voltage Gated Potassium Channels
• Voltage Gated Potassium Channel: Have one
gate on inner side
• Remains closed at rest

12. Sodium Potassium ATPase Pump

16. Roles of Other Ions During the Action
Potential
• Impermeant Negatively Charged Ions
(Anions) Inside the Nerve Axon.
• Calcium Ions