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Bio 220 Lecture 16:
Neurobiology II
I.
Action potential48.7
Today we're going to discuss how
the action potential is propagated down the neuron, and how
it is initiated and passed from one neuron to the
next.
A.
Propagation of action potential along
axon48.8
a. Initiated at axon
hillock near cell body The action
potential is initiated at the axon hillock,
a region of the cell body
at the base of the axon, and
propagatesdown the
axon. As each segment depolarizes, the influx on Na+
leaks into the adjacent
segmentand causing that
segment to initiate an action potential.
b.
Unidirectional
The signal only propagates one
way- away from the cell body and towards the axon tip.
B.
Transmission speed
The action potential is
propagated because Na+ ions flowing in diffuse laterally.
This causes the adjacent region of the axon to reach
threshold. However, some of the Na+ ions are transported
out of the cell, reducing the depolarization.
Factors
that increase the lateral spread of Na+
ionswill increase the
speed of propagation.
Factors that increase the loss of Na+ ions from the cell
will decrease the
speed.
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