Nerve Conduction Flashcards
Draw a diagram of a myelinated nerve and action potential
pg 3
What are the two different types of nerve conduction?
electronic conduction
saltatory conduction
Where are the nodes of ranvier
in b/w the myelin sheathes on a nerve cell
electronic conduction is through a ______ neuron
non-myelinated
saltatory conduction is through a ______ neuron
myelinated
describe how action potential travels vis electronic vs saltatory conduction
much faster via saltatory b/c the myelin sheaths help it travel faster
“conduction velocity” is another way of saying
propagation: a AP traveling down a cell
what are the two passive properties of axonal membranes
time & space
time and space constants are refelctions of what
the physical properties of the neuronal memrane
describe what the time constant tells you
how rapidly a membrane will respond to a stimulus.
the time it takes for the membrane potential change to reach 63% of its final value.
RmCm represents
time constant
what variables represent time constant
RmCm
the time constant represents the amount of time it will take for the membrane potential to reach what percent of its final value
63%
the smaller the time constant, the greater
the propagation velocity
what does Rm stand for
Resistive properties of the membrane
Rm is inversely related to what
permeability
if there is high membrane resistance, there will be
low permeability
increased time constant
What does Cm stand for?
Membrane Capacitance
really generally, membrane capacitance is a fancy way for saying
cell size
the larger the membrane capacitance, the
the greater the amount of charge that must flow to depolarize the membrane, the longer the time constant will be.
What is the equation for the length (space) constant?
√Rmd/Ri4
define the length constant
the distance it takes for the depolarization to decay by 63%
the greater the space constant, the
greater the propagation velocity
What does Rm d Ri stand for in the length constant equation
Rm = membrane resistance d = diameter of axon Ri = internal resistance
Using the length constant, describe why humans have myelinated axons
In order to increase propagation velocity by a factor of 2, the axon diameter has to quadruple because of the square root relationship in the length constant formula. Not practical in humans.
√Rmd/Ri4
another name for length constant
space constant
the propagation veloctiy is directly proportional to what? inversely proportional to what?
directly proportional to the space constant
inversely proportional to the time constant
what has to be done in electronic conduction in order for AP to be propegated along the entire length of the axon?
each adj. region has to be depolarized
what forms myelin
axon wrapped in sheath of schwann cells
what cells surround the axon in the CNS
Oligodendroglial cells
what cells surround the axon in the PNS
schwann cells
where is AP generated in myelnated axon
nodes of ranvier
myelin does what to the membrane resistance & the membrane capitance
increases membrane resistane
decreases membrane capitance
what does myelin do to Cm and Rm
The myelin effectively reduces the Cm and increases Rm to decrease time constant and increase length constant
myelinated axon has greater conduction velocity than an unmyelinated axon fiber that is how much larger in diameter
100x
in unmyelinated axons, what determines the conduction velocity
the diameter of the axon
the larger the diameter of the axon, the greater the speed of propagation
in myelinated axons, what determmines the conduction velociy
the distance b/w the nodes of ranvier
the greater the distance b/w the nodes of ranvier, the greater the velocity of the AP propagation
the larger the membrane capacitance, what happens to time constant
increases time it takes to make depolarization change
longer time constant
large diameter axon compared to small diameter, resistance to flow smaller in which one
the large diameter axon
a lot of resistance what happens to time constant
increases time constant
low resistance to membrane (no myelin) what happens to time constant
what happens regarding capacitance
decrease in time constant
high capacitance
overall take more time for time constant
the more cell membrane needed to charge up, the longer its going to take to
make depolarization change
the shorter the time constant the
faster the velocity propagation
if it has high resistance it likely is a
myelinated neuron
why do you want resistance to be high
so the AP doesn’t leave
think of it as insulation
longer length constant means what
it will move farther before it decays
when you get to node of ranvier you will always trigger a
action potential
capacitance goes way what with myelination
down
in MS what happens
start loosing myelin
what happens to conduction velocity in MS and why
it decreases
b/c resistance of membrane has gone down but capacitance has gone up. so the neurons will act like un-myelinated neuron
what happens to length constant in MS
goes down
what happens to time constant in MS
goes up
for unmyelinated nerve conduction velocity is proprotional to
diameter of axon
myelinated nerve velocity of propagation is determed by
distance b/w nodes of ranvier
