Voltage clamp
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purpose of voltage clamp
control the membrane potential to see which channel is open and how long does it take for it to open
what happens when both membrane potential (Vm) and command voltage (Vc) = -70mV(only K+ channel)?
there is no different in current = no current output
what happens when membrane potential (Vm) = -70mV and command voltage (Vc) = -10mV (only K+ channel)?
since there is a large difference -> large (+) current output (K+ efflux) -> make Vm become -10mV
why does there is a increase current signal detect in the ammeter when membrane potential (Vm) = -70mV and command voltage (Vc) = -10mV?
since the Vm will be brought to -10mV due to K+ efflux -> there is a (+) charge injected to avoid Vm change
according to the voltage clamp when Vm= -10mV, what is the direction of Na+ current?
Na+ current go inward (go down on ammeter graph)
according to the voltage clamp when Vm= -10mV, what is the direction of K+ current?
K+ current go outward (go up on ammeter graph)
according to the voltage clamp when Vm= -55mV, what is the direction of Na+ current?
Na+ current has no inward current (flat line in ammeter) because -55mV is equillibrium potential of Na too
according to the voltage clamp when Vm= -55mV, what is the direction of K+ current?
K+ current has large outward current (go up on ammeter graph)
what substance block Na+ channel?
TTX
how does TTX affect the voltage clamp system?
block Na+ channel -> NO Na+ current in ammeter = inactivation gate close
what substance block K+ channel?
TEA
how does TEA affect the voltage clamp system?
Na+ inward current (go down) -> TEA block K+ channels = No outward K + current
factor determine the conduction velocity of action potential
• size of diameter • myelinate
large diameter axons have _______ conduction velocities
fast
The degree to which the current spreads down the axon depends on two features:
• internal resistance • membrane resistance
internal resistance and membrane resistance become ___ as axon diameter increase
smaller
although the diameter is large, why does only small amount of current pass down axon?
most current lost thru leakage since it take least resistance
larger myelinated axons have _____ conduction velocities
faster
how does damaged myelin in multiple sclerosis affect the action potential?
damaged myelin blocks signal from brain -> AP fail to propagated