These slides explain about nerve impulse generation and action potential

1. Physiology of
NERVE IMPULSE
By
Ms. Keerti H
Dept of OBG Nursing

2. NERVE IMPULSE/ ACTION POTENTIAL
A stimulus is a change in the environment with
sufficient strength to initiate a response.
The nerve impulse causes a movement of ions across the cell
membrane of the nerve cell.
Excitability is the ability of a neuron to respond to the stimulus
and convert it into a nerve impulse.
When a nerve is stimulated, the resting potential changes.
Examples of such stimuli are pressure,
electricity, and chemicals, etc.

3. Different neurons are sensitive to different
stimuli (Although most can register pain). The
stimulus causes sodium ion channels to open.
The rapid change in polarity that moves along
the nerve fiber is called the "action potential.'

4. Resting potential:
* Resting potential may be defined as when there is
variance in voltage between the inside and outside of
the cell as measured across the cell membrane.
* When a neuron is not being stimulated, it maintains
a resting potential Ranges from -40 to -90 millivolts
(mV) Average about -70 mV.

5. Two major forces act on ions in starting the
resting
Membrane is potential:
* Electrical potential produced by unequal
distribution of charges.
* Concentration gradient produced by unequal
concentrations of molecules from one side of the
membrane to the other.

7. When an action potential transfer down the
axon,Polarity modifications occurs across the
membrane.
Once the signal reaches the axon terminal, it
stimulates other
neurons.

8. Steps of the formation of an action potential:
Step 1- A stimulus from a sensory cell or another
neuron causes the target cell to depolarize
toward the threshold potential
Step 2- If the threshold of excitation is reached
all Na+ channels open and the membrane
depolarizes.

9. Step 3 : At the peak action potential, K+ channels
are opened and K-+ begins to leave the cell.
At the same time, Nat channels are
closed.
Step 4 : The membrane becomes hyperpolarized as K+ ions
continue to leave the cell. The
hyperpolarized membrane is in a refractory
period and cannot fire
Step 5 : The K+ channels close and the Na+/K+
transporter restores the resting potential.

12. An action potential comprised of six
phases:
1. Stimulus and Hypopolarization.
2. Depolarization.
3. Repolarization.
4. Hyperpolarization.
5. Resting state.

13. 1. Stimulus and Hypo-polarization:
Stimulus starts the rapid change in voltage or action
potential. In patch- clamp mode, sufficient current
must be administered to the cell in order to raise the
voltage above the threshold voltage to start
membrane depolarization.

14. 2. Depolarization Phase:
Depolarization is caused by a rapid rise in membrane
potential opening of sodium channels in the cellular
membrane, resulting in a large influx of sodium ions.
During depolarization, the inside of the cell
becomes more and more electropositive, until the
potential gets closer the electro chemical equilibrium
for sodium of +61 mV. This is called the overshoot
phase.

15. 3. Repolarization phase:
After the overshoot, the sodium permeability
suddenly decreases due to the closing of its
channels.
The overshoot value of the cell potential opens
voltage-gated potassium channels, which
causes a large potassium efflux, decreasing the
cell's electro-positivity.

16. 4. Hyperpolarization phase:
Hyperpolarization is a lowered membrane
potential caused by the efflux of
potassium ions and closing of the
potassium channels.

17. 5. Resting state:
Resting state is when membrane potential
returns to the resting voltage that occurred
before the stimulus occurred.