1. Nervous Impulse
Action Potential

2. The nature of Nerve Impulse
Nerve impulses are caused by the movement of electrically charged ions. **sodium, potassium**
These messages are caused by a potential or a difference between the inside and outside of the membrane of the neuron

3. Resting potential
When neuron is at rest
More Na+ ions outside
More K+ ions inside
Uses ATP for active transport to maintain concentration difference
Organic negative protein
- Gives overall negative charge inside neuron
To prevent diffusion

4. Action Potential – Up Swing
aka Depolarization
Nerves stimulated by electric shock   pH
Membrane becomes permeable to Na+ ions
Na+ gates open and Na+ diffuses in

5. Action Potential - Downswing
aka Repolarization
Restores negative potential
K+ gates open (membrane becomes
permeable)
- K+ diffuses out
Na+ Gates close

6. Recovery Phase Aka refractory period
Na+ and K+ gates unable to open  ensures action potential doesn’t move backwards
As soon as action potential has moved to next portion of neuron, previous portion undergoes refractory period.
This process requires 1/1000 sec.
(Draw Picture from board)

7. All or Nothing Law
The “All or Nothing” Law states that if the threshold is reached an impulse is carried, but if the threshold is not reached then there will be no impulse. It doesn’t matter how strong the stimulus. The same impulse is sent regardless of strength. The sensitivity to mild or severe pain depends on the number of neurons stimulated as well as the frequency of their stimulation.

8. Action Potential Graph
Depolarization
Repolarization
Refractory
Hyperpolarization

9. Speed of Conduction Non myelinated neuron
Action potential occurs at one small section of a neuron at a time
Non myelinated neuron
Usually occurs in invertebrates/small animals
Action potential moves slowly (0.5m/sec)

10. Myelinated Axon Action potential moves up to 200m/sec
In myelinated neurons action potential concentrated at nodes of Ranvier = saltatory conduction. Action potential jumps from node to node Causes “flip-flop” flow of charge
Animation

11. Action potential Review
Animation