Physiology Muscle Weakness action potentials

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resting cell potential: 60mV
hodgkin hixley and katz: studied squid axon to understand electrical excitability
if the change in a membrane potential during an action potential was due to K+ selectivity changing to non-selectivity what would the AP look like?: the membrane potential would go from Ek to 0mV
where are action potentials ellicited from: the axon hillock
how long ia an AP: milliseconds
when is an action potential graded?: stimulus below threshold
hyperpolarizing
what proof is there that depolarization isnt due simply to K permeability: if it was just K permeability then the AP would only go to 0mV(Ek), instead hodgkin and huxley saw it go to around +40mV, NOT consistent with the "break down hypothesis"
what does the peak of the AP depend on?: extracellular Na concentration
followed the nernst potential for Na
exlain AP in terms of GHK equation: a transient alteration in the permeab
what does alpha from the GHK eqn equal when the membrane becomes non selective: alpha=1
the mechanism of an AP: - Na permeability of axons is V dependent
- At rest NA permeability is low
- when depolarized, Na permeability increases (aloha increases)
- na influx causes further depol and further na influx
explain hodgkin and huxley's volatage clamping technique: membrane potential at a constant controlled level

used TEA (tetraethylammonium) to block K+ conductance
Na conductance increased transiently and then underwent INACTIVATION to normal resting value

K+ conductance was measued (Na blocked by TTX tetrodotoxin), depol caused slower increased conductance and no inactivation
how do you measure ion conductance?: we are measuring I in the cell(know V cause we put it in)
V= IR . . . R = V/I,
conductance is the reciprocal of resistance (g=1/R),
membrane potential at rest permeability alpha voltage: permeable to K
alpha = .05
potential near Ek(-60)
membrane potential at peak permeability alpha: approaches Ena
alpha ~ 20
describe an AP: depol over threshold
NA gates open fast, K opens slower, Na peaks and starts to close fast (around Ena) K starts to close slower, by the time the potential has reached resting state Na is closed but K is still closing thus you get hyperpolarization which gradually gets back to the resting potential
what happens to the graph of AP when you add TEA, tetraethylammonium: broadening and lack of after hyperpolarization
Refractory period absolute relative: absolute - another AP CANNOT happen, slow Na inactivation process must subside after an AP, in area of graph around the peak

relative - K+ conductance subsides(hyperpolarization), need a big stimulus
describe the K and Na channels in terms of gates: Na has both activation(ECM) and inactivation(intracellular) gates.
- in resting state channel is closed and but inactivation gate is open. Depol causes activation gate to open(ECM open), inactivation happens slower but gate on intra side eventually closes. activation gates rapidly return but inactivation takes a while to open again(hence absolute refractory period)

K - only an activation gate which depols and opens, closes slowly when voltage returns to resting level (hence hyperpol)
describe k/na channels: both have sensing elements (aa group) that respond to a change in electrical field

conformational changes are analogous to opening and closing of gates

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