Action potential is a rapid change in membrane voltage due to ion movement, critical for nerve impulse transmission and muscle activation. The process involves depolarization, repolarization, and hyperpolarization, guided by the opening and closing of sodium and potassium channels, following the all-or-none law. Key properties include propagation, biphasic nature, a refractory period, and the influence of myelination on conduction speed.

1. ACTION POTENTIAL
PRESENTED BY SEHELI SINHA
MPT 1ST
YEAR

2. INTRODUCTION
• Action potential is a rapid sequence of changes in the voltage across a membrane by the
help of movement of ion in extracellular to intracellular, and the permeability of each ion.
• In neurons, the rapid rise in potential, depolarization, is an all-or-nothing event that is
initiated by the opening of sodium ion channels within the plasma membrane.The
subsequent return to resting potential, repolarization,
• It is Due to disturbance in the ionic equilibrium across the cell membrane. (Alterations
in the ionic channels)

3. PROPERTIES OF ACTION POTENTIAL
Action potential has four important properties
1. It is propagated.
2. It is biphasic.
3. It obeys all or none law.
4. It has refractory period.
Conduction of impulse through a myelinated nerve fiber is about 56 times faster than through a non
myelinated

4. WHY CELL MEMBRANE NEGATIVE INSIDE POSITIVE
OUTSIDE?
• It has two reasons
A. The concentration of Na+ is higher outside the membrane as compared to inside
B. Presence of non diffusible substance inside the cell membrane Like K+,Cl-,P+Ca+

5. STIMULI
• Electrical
• Mechanical
• Chemical
Importance of AP are
• Transmission of impulse along the nerve fiber
• Release neurotransmitter
• Activate the muscle for the contraction

6. PHASES OF AP
• Latent period: is a short delay (1-2 msec) from the time when the action potential
reaches the muscle until tension
• Depolarisation:A significant influx of sodium ions is produced when the threshold
potential activates voltage-gated sodium chnnels.This period is known as depolarisation.
• Cause –Na+ enter inside cell become more positive
• From – 70 mV to +35mV

7. • Repolarisation: Following the action potential firing, the potassium ion channels that
efflux from the cell open, and the sodium ion channels closed when the cell membrane
overshoot which results in a significant potassium inflow and a reduction in the
electropositivity of cells.
• Cause K+ efflux occur cell become more negative
• From +35 to -70 mV

8. • Hyperpolarisation: This phase possesses more electronegativity in the membrane
potential than in the usual resting membrane potential.
• Cause when K+ start enter into the cell more than normal resting state.
• From -70mV to more negativity

10. SERIES OF EVENTS OF ACTION POTENTIAL
GENERATION
Both K+ and Na+ channel are closed and membrane resting potential is maintained.
A stimulus opens some Na+ channels. If the Na+ influx achieves threshold potential, then additional Na+ gates open, triggering an action potential.
Activation gates of the Na+ channels are open, but the K+ channels remain closed. Na+ ions rush into the cell and the interior of the cell becomes more
positive.
Na+ Channels close and potassium channels open. K+ ions leave the cell and the loss of positive charge causes the inside of the cell to become more negative
than the outside.
Na+ channels are closed, but the slower K+ remains open.

11. HOW TO RESTORE THE ION
• There are two pumps used for this situation
and these pumps use ATP.
1- Na – K pumps (ATPase): pumps 3 Na outside
the cell & takes 2 K inside the cell.
2- Ca pumps: pumps Ca outside the cell or to
Sarcoplasmic reticulum if it’s muscle

12. Absolute refractory period Relative refractory period
Period during which the nerve does not
show any response at all, what ever may be
the strength of the stimulus.
Period during which the nerve fiber shows, if
the strength of stimulus is increased to
maximum
Corresponds to the period from the time
when firing level in reached till .The time
when 1/3 of repolarization is completed.
It extends through rest of the repolarization
period

13. ORTHODROMIC AND ANTIDROMIC
CONDUCTION OF ACTION
ANTIDROMIC CONDUCTION
An axon can conduct impulse in either direction when A.P is
initiated in the middle of segment (2 impulses travelling in
opposite direction by electro tonic depolarization)
ORTHODROMIC CONDUCTION
Impulses pass in one direction only from receptors along the
axon to termination.

14. THANKYOU