1. AP Biology Nervous Systems Part 2

2. Animation http://www.youtube.com/watch?v=90cj4NX8 7Yk http://www.youtube.com/watch?v=90cj4NX8 7Yk

3. Membrane Potential and ion concentrations CYTOSOL EXTRACELLULAR FLUID [Na + ] 15 mM [K + ] 150 mM [A – ] 100 mM [Na + ] 150 mM [K + ] 5 mM [Cl – ] 120 mM [Cl – ] 10 mM Plasma membrane

4. Na+/K+ pumps Cytoplasmic Na + bonds to the sodium-potassium pump CYTOPLASM Na + [Na + ] low [K + ] high Na + EXTRACELLULAR FLUID [Na + ] high [K + ] low Na + ATP ADP P Na + binding stimulates phosphorylation by ATP. Na + K+K+ Phosphorylation causes the protein to change its conformation, expelling Na + to the outside. P Extracellular K + binds to the protein, triggering release of the phosphate group. P P Loss of the phosphate restores the protein’s original conformation. K + is released and Na + sites are receptive again; the cycle repeats. K+K+ K+K+ K+K+ K+K+ K+K+

5. Resting Potential Hyperpolarizations Graded potential hyperpolarizationsGraded potential depolarizations 5 Time (msec) Resting potential 4 32 1 0 Threshold –100 –50 0 Membrane potential (mV) Stimuli +50 Depolarizations 5 Time (msec) Resting potential 4 32 1 0 Threshold –100 –50 0 Membrane potential (mV) Stimuli +50 Action potential 5 Time (msec) Resting potential 4 32 1 0 Threshold –100 –50 0 Membrane potential (mV) Stronger depolarizing stimulus +50 Action potential 6

6. Impulse generation Resting potential Threshold Membrane potential (mV) Action potential Time –100 –50 +50 0 Potassium channel Extracellular fluid Plasma membrane Na + Resting state Inactivation gate Activation gates Sodium channel K+K+ Cytosol Na + Depolarization K+K+ Na + Rising phase of the action potential K+K+ Na + Falling phase of the action potential K+K+ Na + Undershoot K+K+ Na +

7. Propagation An action potential is generated as Na + flows inward across the membrane at one location. Na + Action potential Axon Na + Action potential K+K+ The depolarization of the action potential spreads to the neighboring region of the membrane, re-initiating the action potential there. To the left of this region, the membrane is repolarizing as K + flows outward. K+K+ Na + Action potential K+K+ The depolarization-repolarization process is repeated in the next region of the membrane. In this way, local currents of ions across the plasma membrane cause the action potential to be propagated along the length of the axon. K+K+

8. Saltatory Conduction Cell body Schwann cell Depolarized region (node of Ranvier) Myelin sheath Axon

9. Reflex Arc