1. Nerve Impulse
Every time you move a muscle & every time you think a thought, your nerve cells are hard at work. They are processing information: receiving signals, deciding what to do with them, & dispatching new messages off to their neighbors. Some nerve cells communicate directly with muscle cells, sending them the signal to contract. Other nerve cells are involved solely in the bureaucracy of information, spending their lives communicating only with other nerve cells. But unlike our human bureaucracies, this processing of information must be fast in order to keep up with the ever-changing demands of life.

2. Main idea:Transmission of a Nerve Impulse
Is how the nervous message moves along the length of a neuron

3. Nerve impulse is… An electrochemical message
Created by the movement of IONS across the cell membrane (sodium potassium)

4. Transmission of a signal – THINKING!!!
How is a signal transmitted down/along neuron?
“All or None response”
Think Dominoes!
2007

5. Nerve Impulse is…. Tricky!!!!! VOCAB- Resting Potential
Action Potential
Sodium & Potassium Gates (passive)
Sodium &Potassium Pumps (active)
Depolarization
Repolarization
Recovery

6. Nerve Impulse Order of the Impulse 1- Resting Potential
2-Action Potential
3- Recovery

7. 1- Resting Potential
There is a greater concentration of sodium ions outside the neuron & a greater concentration of potassium ions inside the neuron.
Inside the neuron has a relatively negative charge.
Resting potential is -65 mV
Think KIN (potassium in) K+
Na+ K+
Cl-
aa- + – K+
2007

8. 1- Resting Potential
Resting potential is maintained by the sodium-potassium pumps. (active transport)

9. 2 – Action potential – + + – + – – +
A) Depolarization - a Stimulus causes the Na+ channels to open (change in pH, electric shock, pressure, light)
Na+ ions diffuses into cell
charges reverse at that point on neuron
cell becomes depolarized (+ 40 mV) – + + –
Na+ + – – +

10. How does a nerve impulse travel?
Wave: nerve impulse travels down neuron
change in charge opens other Na+ gates in next section of cell
“voltage-gated” channels
Na+ ions continue to move into cell
“wave” moves down neuron = action potential – + + –
Na+ + – – +
wave 

11. 2- Action Potential + – B) Repolarization: K+ channels open up
K+ ions diffuse out of cell
Restoration of the same potential as resting (- 65 mV)
Causes the channels to close behind impulse + –
Na+ K+
wave 
Opening gates in succession =
- same strength
- same speed
- same duration
2007

12. 3- Recovery + – – + – + + – After firing a neuron has to re-set itself
Na+ needs to move back out
K+ needs to move back in
Sodium Potassium pumps work to re-establish the ion distribution of resting potential
Na+ K+ K+ + – – +
Na+ K+
Na+ – + + –
wave 
2007

13. Neuron is ready to fire again!!!
Na+ K+
aa-
resting potential (- 65 mV) + –
2007

14. Action potential - all together!
Resting potential
Stimulus reaches threshold potential
Na+ channels open; K+ channels closed
Na+ channels close; K+ channels open
Recovery - Na+ / K+ pumps
2007

15. Myelin sheath Schwann cells
insulate neuron (Na+ / K+ cannot enter cell)
Na+ / K+ can only enter at the nodes of ranvier
Increase speed of impulse
signal hops from node to node
150m/sec (330mi/hr) (vs. 5m/sec)
signal
direction
myelin sheath
2007

16. T cells attack myelin sheath loss of signal
Multiple Sclerosis
T cells attack myelin sheath
loss of signal
2007