Handout 20

Handout 20 - Daniel Hans OH: Monday 3-4:00PM Caf Roma...

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Daniel Hans OH: Monday 3-4:00PM Café Roma Handout 2 I. Graded vs. Action Potentials a. Graded Potentials i. How does the amplitude change with distance? decays ii. Is it proportional to stimulus? yes iii. Summation - 2 or more stimuli can be added together Temporal  Summation Several impulses from one neuron over time Spatial Summation Several impulses from several neurons close by iv. Where are they found in the neuron? Dendrites and cell body b. Action Potentials i. How does the amplitude change with distance? It doesn’t ii. Is it proportional to stimulus? Amplitude is not . iii. Can action potentials be summated? nope iv. Where are they found in the neuron? Trigger zone throughout  axon II. Mechanism of Action Potential a. Property How does this feature contribute to action potential? Threshold The current of Na+ ions coming into the cell exceed the current of K+  ions going out of the cell. If depolarization from stimulus exceeds threshold, AP is fired. VG Na+  Channels Depolarization triggers voltage sensor. Na+ activation  gate opens very very fast. Na+ rushes into the cell, down its concentration gradient . Na+ inactivation gate closes channel and Na+ stops
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Daniel Hans OH: Monday 3-4:00PM Café Roma flowing in. VG K+ Channels Depolarization triggers voltage sensor. Channels open very slowly. K+ flows out of the cell, slowly, down its concentration gradient. Absolute  Refractory  Period Another AP cannot be made because inactivation  gates on VG Na+ channels are closed still . Relative  Refractory  Period VG K+ channels are still open, allowing K+ out of the cell making the membrane potential MORE negative than the RESTING MEMBRANE POTENTIAL. So need a stronger stimulus to fire an action potential. b.
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This note was uploaded on 01/31/2010 for the course BILD BIPN100 taught by Professor Fortes during the Spring '10 term at UCSD.

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Handout 20 - Daniel Hans OH: Monday 3-4:00PM Caf Roma...

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