APK 2105C Lecture Notes - Lecture 26: Peripheral Neuropathy, Tetraodontidae, Hypoesthesia
5 Jun 2018
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Chapter 7, Lecture 5
Neurons
• 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
axon
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
directions
▪ Depolarization = positive
feedback to open more Na
channels
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 again—this
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
myelinations
• 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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