AP Biology Nervous Systems Part 2

Animation 7Yk 7Yk

Membrane Potential

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

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+

Impulse generation Resting potential Threshold Membrane potential (mV) Action potential Time –100 – 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 +

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

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+

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

Reflex Arc