1. Graded potential vs action potential
graded potentials – current flow, amplitude
- post-synaptic potentials
Action potentials
Trigger zone
threshold voltage
All-or-none
Channel activity
Refractory period
Coding for stimulus intensity

2. Graded potential – amplitude decreases away from point of channel opening

3. Graded potential
Amplitude is directly proportional to the strength of the stimulating event
Depolarization wave known as local current flow
Strength depends on how much charge enters the cell
Decreases in strength as it travels through the cytoplasm
Can be depolarizing or hyperpolarizing

4. Graded potential – amplitude decreases away from point of channel opening

5. Action potential
Initiated if a threshold depolarization
is reached at the trigger zone
Also called a spike
Always the same amplitude
Amplitude does not diminish
“All or none”, essential for long
distance propogation

6. overshoot
After hyperpolarization
(undershoot)

8. Movement of ions through channels during the action potential
(ion conductance)

9. The voltage gated Na+ channels
Has two gates: an activation gate and an inactivation gate (gate can be opened, gate can be locked)

15. Refractory period
Another action potential cannot fire when the inactivation gate is latched.
Action potentials cannot overlap
The absolute refractory period
Limits the rate of spike frequency
Important for frequency coding

16. Resting membrane potential is not restored,
Na+ channel gates are unlatched (inactivation
Is removed)

17. Coding for stimulus intensity

18. Coding for stimulus intensity

19. NO lecture on Friday Today How are action potentials propagated?
Factors that affect conduction speed
The consequences of abnormal levels of extracellular K+

21. Coding for stimulus intensity

22. Coding for stimulus intensity

23. How does an action potential spread?

24. What causes adjacent voltage gated sodium channels to open?

28. Low resistance to current flow in large diameter axons
Low resistance to current flow in large diameter axons. (wide water pipe)

29. Mammalian axons are very thin, and action potential are conducted quickly.

30. Mammalian axons are insulated by myelin sheaths (myelinated axons).
Saltatory conduction

31. What will abnormally high levels of extracellular K+ cause?

32. Abnormally high levels of K+ will cause
Resting membrane potential will be shifted toward action potential threshold
Get too much excitation (too many action potentials)

33. Abnormally low K+ Membrane resting potential hyperpolarizes
Cell is far away from threshold for action potential