PREPARED BY RASHIDUL HASAN ROBEL B. PHARM (RU), M. PHARM (RU) REG. NO. A4968 PGD-HRM (BIM) EMBA (ULAB)

1. Action Potential
Through
Neuron
PREPARED BY
RASHIDUL HASAN ROBEL
B. PHARM (RU), M. PHARM (RU)
REG. NO. A4968
PGD-HRM (BIM)
EMBA (ULAB)

2. Action
Potential
An action potential is a rapid rise and subsequent fall
in voltage or membrane potential across a cellular
membrane with a characteristic pattern.
It occurs in different cells, called excitable cells, which
include neurons, muscle cells, endocrine cells etc.
5 Steps of Action Potential
1. Resting Membrane potential
2. Threshold (early depolarization)
3. Depolarization
4. Repolarization
5. Hyperpolarization (Undershoot) &
Refractory period (Na⁺/K⁺ Pumps)

3. Membrane
Potential
Positive or negatively charged electrolyte can
cause a difference in electrical charge between
intra-cellular & extra-cellular portion of a neuron.
This is called membrane potential.
Nerve impulse can influence the movement of
electrically charged ions across the cell
membrane.

4. Step-1
Resting
Membrane
Potential
During resting state of neuron,
K⁺ concentration is higher inside the cell membrane with
anionic proteins &
Na⁺ & Clˉ concentration is higher outside the membrane.
The resting membrane potential of a neuron is about -70 mV
(mV means millivolt). It means that the inside of the neuron is
70 mV less than the outside.

5. Step-2
Threshold
Early depolarization is called threshold.
The action potential starts by a stimulus causing the
resting potential moving from -70mV to 0mV.
When the depolarization reaches about -55 mV, a
neuron will fire an action potential. This is the threshold.
If the neuron does not reach this critical threshold level,
then no action potential will start.
In this step, some Na-channel open which cause Na⁺ to
move through the channel into the cell due to stimulus.
Remember, sodium has a positive charge, so the inside
of neuron becomes more positive and becomes
depolarized. Outside of neuron becomes negative.

6. Step-3
Depolarization
After reaching threshold level,
More Na-channel open which cause huge Na⁺ to
move through the channel into the cell. So the inside
of neuron becomes more positive and becomes
depolarized.
And the membrane potential reaches from -55mV to
+40mV.

7. Step-4
Repolarization
After depolarization (huge Na⁺ inside the neuron
& membrane potential reaches +40mV),
Na-channel inactivated & K-channel open which
cause K⁺ to move through the channel outside
the cell. So the outside of neuron becomes more
positive and becomes repolarized. Clˉ moves
from outside to inside that turns into negative.
And the membrane potential falls from +40mV to
-70mV.

8. Step-5
Hyper
polarization
During hyperpolarization,
The voltage-gated K-channels stay open a little
longer than needed to bring the membrane back to
its resting potential. But Na-channels become closed
.This results in a phenomenon called undershoot, in
which the membrane potential more lower (more
negative -75mV) than its resting potential -70mV.
After that, K-channels are closed. No more K⁺ moves
from inside to outside of membrane.

9. Refractory
Period
The slow closure of the voltage-gated potassium
channels, which results in undershoot, also
contributes to the refractory period by making it
harder to depolarize the membrane (even once the
voltage-gated sodium channels have returned to their
active state).
During refractory period, both Na & K-channels
remain closed.
The refractory period ensures that an action potential
will only travel forward down the axon, not backwards.

10. Refractory
Period
During refractory period,
Interestingly Na⁺/K⁺ ATPase pumps are activated
by an ATP molecule. Then the pump allows 2K⁺
move inside the cell in exchange of 3Na⁺ outside
that results into reaching resting membrane
potential.

11. New
Action
Potential
When the action potential reaches the axon terminal
(nerve ending), it causes neurotransmitter-containing
vesicles to fuse with the membrane, releasing
neurotransmitter molecules into the synaptic cleft
(space between neurons).
When the neurotransmitters bind to ligand-gated ion
channels on the receiving cell, it may cause
depolarization of that cell, causing it to undergo its
own action potential.

12. +40 mV
-75 mV
❶
❷
❸ ❹
❺
Schematic Diagram
of
Action Potential
❶Resting Membrane potential
❷Threshold (early depolarization)
❸Depolarization
❹Repolarization
❺Hyperpolarization (Undershoot)
(Refractory period)
-55 mV
❶

13. Figure of
Action Potential

14. Movement of
electro-chemical
charge through axon

15. Thanks
for
watching …