#13 Flashcards
AP All-or-None
Occurs or doesnt.
Once an AP starts, whole thing occurs
Absolute Refractory Period
Short period right after AP, impossible to initiate another AP
Relative Refractory Period
Short period right after AP, possible to initiate another AP but requires STRONG stimulus
Overshoot
Peak of AP
Vm > 0mV
Bernstein Hypothesis
Membrane breakdown allows current in and out
Largest depolarization = 0mV
Big, nonselective hole would have Vrev = 0
Hodgkin & Katz Hypothesis: Sodium Hypothesis
Cell increase in Na
Max depolarization = Ena
Na Hypothesis Test
Incrementally reduce NaOut until no AP occurs
Voltage Clamp Theory
Control Voltage and measure current
AP Initiation Conductance
Due to increase in gNa
AP Termination Conductance
Decrease in gNA
Increase in gK
What determines changes in conductance?
Vm
Na Hypothesis Measuring Current Ik and INa
From measurements, deduced g at each V
Why is it hard to control voltage of a cell?
Resistance of the electrodes causes voltage drop
V = I * R
Why use giant squid axon?
Axon so large, allows use of small wire to measure V and pass I
Vcommand Control (Maintain = to Vm)
Pass I constantly and dynamically to keep Vm constant
Measure change in CURRENT I!!!
Isopotentiality
Measuring I difficult because V varies over axon d/t longitudinal resistance
Solved with wire directly in center
iM (Total Membrane Current) of Passive Neuron
= iLeak + iCapacitor
iCapacitor
Changes to compensate for change in Vm
