1. Action Potentials
Department of Biology, WCU

2. Introduction Electricity Measured in mV Potential Current
neutral, positive, negative
Measured in mV
Potential
Current
resistors (plasma membrane)
Conductor (axon)

3. Plasma membrane Proteins as channels Passive vs active Protein gates
Respond to:
chemicals (synapse)
Voltage (along an axon)
Electrochemical gradient

4. Resting membrane potential
Measurement
-70 mV
across plasma membrane

5. Resting membrane potential
Due to diffusion gradient and voltage gradient

6. Membrane potentials Changes result of: Types of signals
1. Permeability of ions
2. Ion concentration
Types of signals
Graded potentials
Action potentials

7. Membrane potentials Depolarization Hyperpolarization
Inside of cell less negative than RMP
Hyperpolarization
Inside of cell more negative than RMP

8. Graded potentials Short distance, short lived Reason for “graded” name
Types
1. Receptor potential (light)
2. Postsynaptic potential (EPSP or IPSP)

9. EPSP’s
Influx of Na+ causing a depolarization
Never reaches threshold

10. IPSP’s Increase in K+ or Cl- permeability
No effect on Na+ permeability

11. Summation
Neural integration
Types
temporal
spatial

12. Action potentials Characteristics occurs along the axon
stronger stimulus, “All or nothing”
no decrease in strength
unidirectional

13. Action potentials
Phases
1. Resting membrane potential

14. Action potentials
2. Depolarization
- increase in Na+ influx (5,000 x)

15. Action potentials 3. Repolarization decrease in Na+ influx
increase in K+ efflux (10 x)

16. Action potentials 4. Hyperpolarization sluggish K+ gates
potential restored by Na/K pump

17. Characteristics 1. Unidirectional AP’s are discrete events
propagation of impulse

18. Propagation of impulse

19. Propagation of impulse

20. Absolute refractory period
Voltage gated Na+ gates are open

21. Characteristics
2. Threshold stimulus
stimuli must be mV

22. Characteristics 3. All or none phenomenon 4. Stimulus intensity
it either occurs or it does not
4. Stimulus intensity
firing at a set intensity (can increase)

23. Characteristics 5. Refractory period absolute (already discussed)
relative period
will only fire with a stronger stimulus

24. Relative refractory period
Re-open Na+ gate with a stronger second stimulus

25. Summary
Integration of potentials
EPSP/IPSP’s
GP’s
GP’s
AP’s
AP’s