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AP Biology

AP Biology. Nervous Systems Part 2. Animation. http://www.youtube.com/watch?v=90cj4NX87Yk. CYTOSOL. EXTRACELLULAR FLUID. [Na + ] 150 m M. [Na + ] 15 m M. Membrane Potential and ion concentrations. [K + ] 150 m M. [K + ] 5 m M. [Cl – ] 120 m M. [Cl – ] 10 m M. [A – ] 100 m M.

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AP Biology

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  1. AP Biology Nervous Systems Part 2

  2. Animation • http://www.youtube.com/watch?v=90cj4NX87Yk

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

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

  5. Stimuli Stronger depolarizing stimulus Stimuli +50 +50 +50 Action potential Resting Potential 0 0 0 Membrane potential (mV) Membrane potential (mV) Membrane potential (mV) Threshold Threshold –50 –50 –50 Threshold Resting potential Resting potential Resting potential Depolarizations Hyperpolarizations –100 –100 –100 1 1 4 1 4 0 0 5 2 3 0 6 2 3 5 2 3 5 4 Time (msec) Time (msec) Time (msec) Graded potential hyperpolarizations Graded potential depolarizations Action potential

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

  7. Axon Action potential Na+ Propagation An action potential is generated as Na+ flows inward across the membrane at one location. Action potential K+ Na+ 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. Action potential K+ Na+ 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.

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

  9. Reflex Arc

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