1. Neural Communication: Action Potential
Lesson 9

2. Neural Signaling: Axon
Action Potentials
propagated electrical signal
regenerated
Large & rapid changes in Em
depolarization
repolarization ~

3. Action Potentials Electrically-gated channels or voltage-gated
Characteristics
all-or-none
relatively slow
non-decremental ~

4. Threshold of Excitation
also: threshold potential
Triggered at axon hillock
point of decision
integration
Threshold potential
Depolarization;
approximately 10 mV
EPSPs  AP ~

5. -70
-60
+40
-80
Time Em

6. Em drive Na+ into cell +40 -60 -70 -80 Time C & E gradients
Depolarization
Na+ influx Em
-60
-70
-80
Time

7. Na+ + - K+

8. Na+ + - K+

9. +40
Repolarization
K+ efflux Em
-60
-70
-80
Time

10. Na+ + - K+

11. Na+ + - K+

12. +40
After-
hyperpolarization Em
-60
-70
-80
Time

13. Refractory Period After AP time-out prohibits or resists AP
absolute & relative ~

14. Refractory Period Absolute refractory period Na+ channels deactivate
will not trigger AP
must reset
one-way transmission of signal
Ball & Chain Model ~

15. Na+ channel deactivation

16. Na+ channel deactivation

17. Refractory Period Relative refractory period
during after-hyperpolarization
requires greater depolarization to reach threshold ~

18. Frequency Code Intensity of stimulus frequency of APs Pattern
Type of stimulus
Brain area that receives signal
Visual, auditory, pain, etc.
Doctrine of Specific Nerve Energies ~

19. FREQUENCY CODE Weak stimulus 1. Moderate stimulus 2. Strong stimulus3.

20. Saltatory Conduction Myelinated neurons
oligodendrocytes & Schwann cells
Long distances transmission
APs relatively slow, regenerates
EPSPs - fast, decremental
Saltatory: combines both types of current
speed without loss of signal ~

21. Saltatory Conduction Nodes of Ranvier action potentials no myelin
Myelinated portions
passive current
decremental but triggers AP at next node ~

22. Saltatory Conduction
Nodes of Ranvier

23. PSPs vs APs Graded Summation longer duration 10-100 msec
chemical-gated
passive spread
instantaneous
decremental
All-or-none
short
1-2 msec
voltage-gated
propagated
slow
nondecremental