1. The Action Potential

2. The Resting Potential of the Neuron
results from difference in ion distribution inside and outside of cell (-70mV)

4. Forces Behind Resting Potential
Selective Permeability- some molecules pass through membrane more freely than others; ion channels
Sodium-Potassium Pump transports 3 Na out of, 2 K into cell
Result:
Concentration Gradient
Electrical Gradient

7. Forces Behind Resting Potential
What would you do to generate electrical signal fast?
RP takes work (Na/K Pump). Why do we bother?

8. Molecular Basis of Action Potential
Sodium channels open once threshold is reached, influx of sodium
Potassium channels open at AP peak; potassium flows out

11. The All-or-None Law
The size, amplitude, and velocity of an action potential are independent of the intensity of the stimulus that initiated it.
How then is stimulus intensity coded?

13. Figure 2.20  Saltatory conduction in a myelinated axon An action potential at the node triggers flow of current to the next node, where the membrane regenerates the action potential.

14. The Action Potential The RefractoryPeriod Absolute Refractory Period
Sodium gates are firmly closed
Membrane cannot produce AP, regardless of the stimulation.
Relative Refractory Period
Sodium gates in usual state, but the potassium gates remain open.
Stronger than normal stimulus needed for action potential.

15. Propagation of the Action Potential
From: Axon Hillock
To: Terminal Buttons
AP travels in one direction only. WHY?

16. The Myelin Sheath and Saltatory Conduction
Myelin Sheaths increase the speed of neural transmission
Nodes of Ranvier-Short area’s of the axon that are unmyelinated
Saltatory Conduction-jumping action of actions potentials from node of Ranvier to node of Ranvier

18. Signaling Without Action Potentials
Depolarizations and hyperpolarizations of dendrites and cell bodies
Small Local neurons-produce graded potentials (membrane potentials that vary in magnitude and do not follow the all-or-none law)