Lecture on October 1st: The Action Potential (Continued)

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Psychology & Brain Sciences
Lori Astheimer Best

Behavioral Neuroscience, Lecture on October 1 st Refers to chart: Chlorine has an equal force with diffusion and electrostatic keeping it out. Potassium- diffusion is greater which is why we need the pump to keep them inside. Resting potential -60 to -70 Action potential, 1) threshold when it hits above a certain voltage. Depolarization through EPSPs. Sodium channels open, sodium enters the cell. Voltage is changed enough so the shape of the cell changes. Occurs at the axon hillock. 2) depolarizing. Voltage gated potassium channels enables the potassium channels to open, potassium begins to leave the cell. 3)peak of the action potential (40+) potential stops once the sodium channels close and go into a refractory period. No more sodium can enter the cell so no more positive ions can enter. 4) hyperpolarizing. Potassium ions rapidly leave the cell, causes the membrane potential to return to resting level. 5) return to negative resting potential. Potassium channels close and sodium channels are now reset and can open again once depolarized. 6) hyperpolarized briefly. Cell gets more negative because the potassium channels close more slowly and so much potassium rushes out of the cell that the cell ends up getting more hyperpolarized. We have a lot more potassium outside the cell than inside the cell. How do we recover from this? Extra Potassium outside of the cell diffuses away into extracellular space. Refractory period, Absolute refractory period is when there is no way to generate another action potential because the sodium channels already open or they are closed in the refractory state. No amount of stimulation can cause another potential. Gives the neuron time to recover. Relative refractory period, neuron is hyperpolarized and only strong stimulation will cause another action potential.
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