Electrical Excitability and Action Potentials Flashcards
How much biger is the peak of the action potential to Vrest
~100mV
What is the overshoot?
part of AP that lies above the 0mV
What 3 factors influence the threshold, amplitude, time course, and duration of the action potential
the gating and permeability of ion channels (depend on Vm and time)
- the intra and extracellular concentration.
- membrane properties, capacitance resistance and the geometry.
What does a brief action potential reflect?
rapid signaling (e.g nerve axon)
what does a prolonged repetitive AP tell.
slower rhytmic contractions (cardiac and certain smooth muscle cells)
what does endothelin do?
shorten the duration of AP.
τ =
RC (product of membrane resistance and capacitance
what does happen to graded responses with distance?
decays
what happens with AP with distance
magnitude and shaoe stay same. however delay between stimulus and response increases.
What are graded voltage changes
yperpolarizations and subthreshold depolarizations
what is electrotonic conduction
As the graded response spreads, its magnitude decays exponentially with the distance from the site of stimulation because of passive loss of electrical current to the medium.
What kind of velocity do AP propagate
constant (130m/s)
Does a large stimulus have a long duration
large stimulus short duration
small stimulus long duration. of spike
What is the refractory period
time where it is (nearly ) impossible to fire AP
The absolute refractory period lasts from?
initiation to when repolarisation is almost complete
What is a feature of the absolute refractory period?
no second AP can be fired
whe does the relative refractory period start
after absolute refractory to almost Vrest
what is a feature of the relative refractory period
the minimal stimulus necessary for activation is stronger or longer than predicted by the strength-duration curve for the first action potential
is the current-voltage relationship between NA+ and K+ macrop or micro scopic? and why
macroscopic because the currents represent many individual ion channels
why are the K channels called delayed rectiefier K+?
activate with a time delay
ix=gx(Vm-Ex) explain the parameters
ix is the single channel current.
gx is the single channel conductance.
what is ohmic in a graph
linear
what is Boltzman distribution
The probability of a channel’s being open depends on V m
Ix=NPoix
What is P the probability that the channel is open.
what are the parameters of Hodgkin and Huxley (not full names)
n,m,h dimensionless parameters between 0 and 1
what do the parameters mean of Hodgkin and Huxley (n,m,h)
activation parameter n= the probability that the K + channels are open.
activation parameter m= the probability that the Na + channels are open.
the inactivation h- Na + current inactivates,
when are the parameters of Hodgkin and Huxley measured
at infinite time (e.g steady state)
what causes depolarisation
increase in Na + conductance
what causes repolarisation
inactivation of Na + conductance and delayed activation of K + conductance
what can be the external stimulus to activate Na+ channels at AP
electrode, a synaptic event, or propagation of a depolarizing wave
what is a gating current
small movement of charge that should accompany the activasion of voltage gated Na and K channels
what are receoptor and synaptic potentials
graded responses
what are two ways in improving conduction properties of nerve fibers
increase diameter of axon (higher conductance)or
myelinating the fiber
what are Schwann cells
glial cells that produce myelin in the periphery
what are oligodendrocytes
glial cells that produce myelin in the brain.
what does myelin do
increase membrane resistence which minimizes loss of current.
what are the nodes of Ranvier
unmyelinated zones, containing a large density of voltage gated Na+ channels.
where are the Na channels in the nodes of ranvier
nodal membrane
where are the K channels in the nodes of ranvier
paranodal regions flanking each node
what is saltatory conduction
impulse conduction where, Current flow that is initiated at an excited node flows directly to adjacent nodes with little loss of transmembrane current through the internode region
what is more effecient and propagates AP faster myelin or larger diameter
myelin (130 m/s)
is there a transmembrane current in internodal regions?
no, only capacitative current.
what are electrotonic currents
decaying currents that spready away of the location of the electrode.
what are the two cable parameters?
time and length constant
when myelinated fibers with a very small diameter (<1 µm), is conduction than faster than unmyelinated axons with the same outeer diameter.
no, becasue the resistance of the axoplasm dominates.
what is multiple sclerosis
autoimmune disorder in which the myelin sheath surrounding CNS axons is progressively lost, eventually resulting in nerve blockage
a high h favors the …state of the channel.
open
