1. Biology 12
Neuron Function

2. Joke of the day:

3. What is a nerve impluse? Neurons carry messages as electrical impulses
It comes from:
Another neuron
A sensory receptor
Here we are looking at how an impulse travels within one neuron, down the axon!

4. For an impulse to be sent there must be a difference in electrical charge between the inside and the outside of the cell.
Also called an ACTION POTENTIAL

5. Electrical Charge: Sodium (Na+) Potassium (K+)
Found inside and outside of neurons
Since both are positive…. It`s all relative!
Positive = more positive ions
Negative = fewer positive ions

6. Step 1: Resting potential
Not sending an impulse
Neuron is polarized
When a neuron receives a stimulus, the cell is ready/armed to transmit the signal by having a charged difference across the membrane
Neuron impermeable to Na+
Na+ collects outside
K+ moves freely (permeable)

7. Step 1: Resting potential
Outside is positive
All Na+ and some K+
Inside is negative
Some K+
Polarized

8. Step 2:Action Potential
When a neuron is excited by a stimulus, the cell membrane become highly permeable to Na+ ions
Na+ channels (gates) open
Na+ diffuses (moves) into cell
The negative charge become positive inside the cell

9. Step 2: Action Potential
Polarity reversed
Inside positive
Outside negative
Depolarized

10. Step 2: Action Potential
Note: Na+ gates are only open for a fraction of a second
Na+ gets trapped inside the cell

11. Step3: Refractory Period
Na+/K+ pumps returns membrane to rest
Na+ moves out
K+ moves in
Repolarized
Outside now +
Inside now –
Neuron is now returned to “resting potential”

12. “Like a wave” Depolarization occurs in a small area
Affects adjacent gates
Creates “wave” of electricity
Travels length of axon

13. “wave pictures”

14. Threshold:
Minimum strength stimulus required for action potential to occur
NOT all stimuli can cause action potential
Different for each neuron

15. All or None Response: Impulses are all alike once threshold reached
Different strength of stimuli are detected depending only on number of impulses sent
Greater the number of impulses reaching the brain the great the response

16. Graph of Action Potential
Na+ channel closes
Na+ channel opens

17. Animations:
Resting Potential:
Action Potential

18. To do :
Read pages
Page 426 #3, 4, 6, 7, 8, 10, 11