APK 2105C Lecture Notes - Lecture 26: Peripheral Neuropathy, Tetraodontidae, Hypoesthesia

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Chapter 7, Lecture 5
AP frequency
o Coding for stimulus strength
The hillock can stay depolarized to
threshold for several msec
Stays depolarized during stimulus
Refractory period is usually about 15 msec
If the stimulus lasts for long enough (as
long as the refractory period) you can get
multiple AP
Suprathreshold stimulus that is long
will be able to send the most APs
AP propogation
o AP generation happens at the axon hillock
Summation of enough graded potentials to be able to generate an AP
Lots of voltage gated Na and K channels
o Happens unidirectionally down the
o Site A is region of depolarization
Inside of cell is more positive
than outside of cell
Different from normal
Na that rushes into the cell
spreads out in lots of
Depolarization = positive
feedback to open more Na
o Propogation = Na that rushes in
causes the sites further down the
axon to start depolarizes
Once it moves down to Site B,
Site A goes into refractory period and the Na channels close againthis
explains why the AP moves down the axon only
Get exact same amount of depolarization at every site
Saltatory vs. electrotonic propogation
o Have to be considered when the axon is myelinated
o Electrotonic propogation = happens Na channel by
Na channel
Somewhat slower processes
o Saltatory propogation = takes larger steps
Nodes of ranvier = gaps between
Have large conc of Na channels
Na comes in in these areas
In the areas where there is myelination
Large amounts of electrical insulation
Very hard for ions to move around
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