Exam 2 Flashcards
what controls the firing pattern of action potentials? what channels are open when?
resting channels are always open
ligand gated channels open as the AP reaches threshold
V-gated ion channels open once neuron reaches threshold
are resting membrane potentials ohmic
yes
are action potentials ohmic
no
who came up with the voltage clamp method
Kenneth Cole
what is the voltage clamp method
it holds V (membrane potential) constant so you can measure ion currents
works bc of gNa = INa / (Vm - ENa)
ENa is always constant
method is holding Vm constant
what is a profuse axon? how do you get one
an axon with all of the axoplasm removed
1) flush out squid axon (remove proteins)
2) replace w salt solutions
3) insert electrode
4) measure membrane potential
what did the profuse axon show in Cole’s experiments
almost identical action potential to normal –> the action potential is entirely controlled by membrane proteins and not intracellular proteins
describe the feedback loop of an action potential
positive
Inward Na current –> inc depolarization –> inc Na channel opening –> inc inward Na current
How does the permeability of K, Na, and Cl compare during rest and during AP
K stays almost same
Cl stays almost same
Na increases about 500x (almost impermeable to very permeable
what ion change is responsible for the rising phase of APs?
Na
what ion change is responsible for the falling phase of APs?
K
what happens to the Na if you inc/dec Na?
inc Na –> higher peak
dec Na –> lower peak
end stays the same
what was Hodgkins and Katz’s hypothesis
depolarization of a cell to a membrane potential above threshold causes a brief inc in the mem permeability to Na ions
Hodgkin and Katz formula
gNa = INa / (Vm - ENa)
a voltage clamp setup involves…
injection of a variable current to hold membrane potential constant
What is TTX
Na channel blocker
What is TEA
K channel blocker
what makes up the total current across the membrane
the Na current + the K current
which current starts first? Na or K?
Na
what current do yo get when using TTX? describe the shape of the current
K
looks sigmoidal –> delayed start, s shaped curve leveling out at top
what current do you get when using TEA? describe the shape of the current
Na
looks like upside down bell curve with long right tail –> starts sooner and ends at 0
which current is transient (Na or K)? what does this mean
Na is transient
it lasts a short time and returns to 0
does conductance increase or decrease with increasing depolarization
increase
compare v-gated Na and K channels opening in response to membrane polarization
they both open when depolarized
compare v-gated Na and K channels probability of opening with changing depolarization size
both inc chance of opening with inc depolarization
