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PMCOL 371 Midterm Exam Latest Update
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PMCOL 371 Midterm ExamLatest Update
Formula for time constant of r//c - Answer T= rm x cm, can find capacitance from
measured T
Charging formula - Answer V=iR (1-e^-t/T)
e^-1 is 0.37, so after one T of charging the voltage is 63% of the max value
Discharging formula - Answer V=iR (e^-t/T)
e^-1 is 0.37, so after one T of discharge the voltage is 37% of the max value
Voltage and length constant formula - Answer Vx=Vo(e^-x/y) where y is length constant
and x is distance from injection point
Length constant formula - Answer y=square root of (rm/ri) (membrane resistance/axial
resistance)
Capacitor formula - Answer C=Q/V
Q=C/V
Nernst equation - Answer Ek=(RT/ZF) ln (Ko/Ki)
Z is valence
At 20 degrees, Ek= 58mV log (Ko/Ki)
For divalent divide by two, for anions add negative
Goldman-Hodgkin-Katz equation - Answer Vm = 58log((Pk[k]out+PNa[Na]out +
PCl[Cl]in)/(Pk[k]in+PNa[Na]in)+ PCl[Cl]out )
You can use 58 because all ions are monovalent and you flipped Cl to reverse the
charge
Ik (delayed rectifier) - Answer -Delayed sigmoidal opening with multiple pre open states
-Preferentially conduct out due to only being open at positive voltages and due to K
gradient
-Repolarizes AP
-Inactivates with longer current pulses, not on AP timescale
, M channels (Im) - Answer -Open slowly with depolarization (too slowly to act within a
single AP)
-Do not inactivate
-Limits repetitive AP discharge
-Closed by ACh acting at muscarinic, causes excitatory central cholinergic effects
(hyperexcitable)
-Activated by retigabine
Retigabine - Answer Im potassium channel opener/activator
-Lowers resting potential to suppress excitation, hyperpolarizing shift in
voltage-dependence (open at lower voltages), helps with epilepsy
Maxi K, Ca channels (BK channels) - Answer -Depend on depolarization and intracellular
calcium
-High unitary conductance
-Intrinsic Ca-sensing mechanism
Iahp channels (SK channels) - Answer -Weakly voltage dependent, strongly Ca
dependent
-Low conductance
-Influx of Ca with APs activates channel to produce slow afterhyperpolarization (less Ca
means no AHP), relevant for bursts in rhythmic activity
-Extrinsic CA sensing via calmodulin binding site
-Blocked by apamin
Apamin - Answer Blocks Iahp/SK, prevents slowing of APs after bursts
A-currents (Ia) / transient currents - Answer -Activated by depolarization
-rapid inactivation by ball and chain (N-type)
-To reactivate, must hyperpolarize
-Example of encoding: higher stimulus causes Na to win over repolarizing, Ia cannot
recover, and APs happen at at a higher frequency
KIR (inward rectifiers) - Answer -Pass current easier inward, but never do under
physiological conditions
-Allow small outward current near rest to maintain Vrest
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