1. Do Now: 1. What is 1 of the characteristics of nerve signals that you defined from the “dominos” lab? 2. What is the role of the axon? 3. What creates electrical signals? 4. What creates chemical signals?

2. What is the Action Potential?
How neurons send signals electrically down their axons.
Neurons do this by using their membrane potentials.
What does electricity mean?

3. So, what is a Membrane Potential?
Membrane potentials come from the charge of the axon cell membrane.
When neurons are NOT sending a signal, their cell membrane is negative!

4. So, what is makes a cell membrane negative?
Ions!
Chloride ions (Cl-) sit in the cell membrane and make it negative. They will not move
Outside
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Inside
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Outside

5. To create an action potential, we have to let ions move!
Can ions just flow into the cell?
We need ion channels!
How do we open ion channels
at the synapse?
Do you think all ion channels
open that way?

6. Voltage-Gated Ion Channels
They only open up when the cell membrane changes charge!

7. Two ions are responsible for nerve signaling:
Sodium (Na+) has high concentration (more of it) outside the cell when there is no signal.
Potassium (K+) has high concentration inside the cell when there is no signal.

8. Neuron before signal looks like this!
Sodium ions are mostly outside!
Potassium ions are mostly inside!
Cl- K+
Outside
Inside
Na+

9. Ion mostly inside cell
Ion mostly outside cell
Charge inside cell
Charge outside cell
Signal?

10. +70
(membrane potential)
Charge
+50
-70
Time

11. So, we need to send a signal. What happens?
The neurotransmitter will open
up sodium channels at the synapse!
This will then make voltage sodium
channels open up nearby
What do you think is happening to the
charge of the cell?

12. Sodium turns ON an action potential
Needs a small change in charge!

13. Neuron when signaling looks like this!
Sodium ions are mostly inside!
Potassium ions are mostly inside!
Cl- K+
Outside
Inside
Na+

14. +70
(membrane potential)
Charge
+50
-70
Time

15. Ion mostly inside cell
Ion mostly outside cell
Charge inside cell
Charge outside cell
Signal? K+
Na+
Negative
Positive No

16. Potassium turns OFF an action potential
Needs a BIG change in charge!

17. Neuron when stops signaling looks like this!
Sodium ions are mostly inside!
Potassium ions are mostly outside!
Cl- K+
Outside
Inside
Na+

18. +70
(membrane potential)
Charge
+50
-70
Time

19. Ion mostly inside cell
Ion mostly outside cell
Charge inside cell
Charge outside cell
Signal? K+
Na+
Negative
Positive No
None
Yes

20. Now we need to reset! We need to go back to where we started.
Which ion should be outside the cell?
Which ion should be inside the cell?

21. The sodium-potassium pump resets it.
It uses energy to exchange 3 sodiums for 2 potassiums to bring it back to the starting position.

22. +70
(membrane potential)
Charge
+50
-70
Time

23. Ion mostly inside cell
Ion mostly outside cell
Charge inside cell
Charge outside cell
Signal? K+
Na+
Negative
Positive No
None
Yes