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Lecture 5

PSYC 4640 Lecture 5: actionpothandout

1 Page
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Fall 2015

Department
Psychology
Course Code
PSYC 4640
Professor
Kelly
Lecture
5

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1. The neuron’s resting potential is -70mV; the charge is slightly negative inside the cell
relative to outside the cell.
2. At rest, Na+’s concentration and electrical gradients are driving it into the cell, but its
gates are closed.
3. At rest, K+’s concentration gradient is driving it out of the cell, and its electrical gradient
is driving it into the cell, but its gates are closed.
4. Once threshold is reached [~ -55mV], an action potential occurs. Na+ gates open wide
and Na+ rushes into the cell, the charge overshooting 0 so that the cell becomes
positively charged [inside]. This causes Na+’s electrical gradient to now drive it OUT of
the cell – this opposition of gradients closes the Na+ gates.
5. At about the peak of the action potential, K+ gates open, and now its concentration and
electrical gradients [its positive inside now] are driving it out of the cell, so much so that
it eventuates in hyperpolarization of the membrane.
6. Eventually, things right themselves [with some help from the Na+/K+ pump] and the
neuron returns to its resting potential.
7. The neuron can’t immediately refire because of its refractory period.
8. Recall all or none law – once that threshold [-55mV] is reached the intensity of the
stimulus is irrelevant – it may be the #, or the pattern, of neurons firing.
9. On neurons without myelin, information travels down the axon via propagation, never
losing strength as a new potential is created at each point along the axon.
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Description
1. The neurons resting potential is 70mV; the charge is slightly negative inside the cell relative to outside the cell. 2. At rest, Na+s concentration and electrical gradients are driving it into the cell, but its gates are closed. 3. At rest, K+s concentration gradient is driving it out of the cell, and its electrical gradient is driving it into the cell, but its gates are closed. 4. Once threshold is reached [~ 55mV], an action potential occurs. Na+ gates open wide and Na+ rushes into the cell, the charge overshooting 0 so that the cell becomes positively charged [inside]. This causes Na+s electrical gradient to now drive it OUT of the cell this opposition of gradients closes the Na+ gates. 5. At about the peak of
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