Module 6.3 - H&H's Mathematical description of the AP

Question 1

Of the three currents observed by H&H, what did the capacitive current represent?

Answer 1

Current required to change the voltage

Question 2

Of the three currents observed by H&H, what did the early inward current represent?

Answer 2

Na+ influx

Question 3

Of the three currents observed by H&H, what did the late outward current represent?

Answer 3

K+ efflux

Question 4

What four things did H&H achieve with their mathematical description of the AP?

Answer 4

1. Used voltage-clamp to record voltage-gated sodium and potassium channel currents at different fixed voltages
2. Mathematically converted recorded currents to conductances
3. Derived equations that mathematically simulate conductances at different voltages
4. Used these equations to define the change in voltage over time over the course of an AP

Question 5

How did H&H transform the recorded Na and K current into conductance curves?

Answer 5

Using Ohm’s Law (e.g., GK = IK/(Vm-EK))

Question 6

What happens to the peak Na and K conductances at stronger depolarization ?

Answer 6

Peak Na and K conductances increase with stronger depolarization towards a maximal value

Question 7

Define these equations and their variables:
GK(t) = GK(max)n^4
n = 1-e-(t/Tn)

Answer 7

GK(max) is maximal conductance
t = time
Tn = voltage-dependent parameter
Plugging in these values into GK(t) simulates K+ conductance curve

Question 8

Define these equations and their variables:
GNa(t) = GNa(max)m^3h
m = 1-e-(t/Tm)
h = e-(t/Th)

Answer 8

GNa(max) = maximal conductance
t = time
Tn = voltage
GNa(t) simulates Na+ conductance curve

Question 9

Outline the steps taken by H&H to simulate the AP. (6)

Answer 9

1. Assumed a mild depolarization of Vm takes place at t = 0.01 ms
2. Used this new Vm to determine new GNa and GK at t = 0.01 ms
3. Used the new conductances to determine new total Na+ and K+ currents acting on membrane at t =0.01 ms
4. Calculated the change in Vm that resulted from the increased INa and IK values
5. Summed the change in Vm and the previous Vm to give Vm at t = 0.02 ms
6. repeated steps 2-5 repeatedly to simulate the conductance curves over the course of an entire AP

Question 10

What Nobel prize did H&H win for their research?

Answer 10

1963 Nobel Prize in Physiology or Medicine