Conduction

Question 1

( d^2 V/ d x^2 ) = -r. di/dx

Answer 1

the cable equation
r= internal resistance (causes V drop)
x= distance

Question 2

the cable equation describes

Answer 2

AP moving along a nerve axon with the assumption that the bath or fluid outside the cell is highly conductive

Question 3

the cable equation components:
drop in potential difference due to?
loss of current inside cable is balanced by?
Change currents to what model?

Answer 3

internal resistance
the current leaving the cable across the membrane
Hodgkin and Huxley membrane model

Question 4

Sub-threshold stimulus

Answer 4

refers to a stimulus that is too small in magnitude to produce an action potential in excitable cells.

Question 5

membrane length constant

Answer 5

lambda m= sqrt( rm/ra)

Question 6

Membrane time constant

Answer 6

tau m= r.c

Question 7

Factors determining conduction velocity

Answer 7

Fibre diameter -velocity is higher in larger fibers
Length constant (how far the currents
associated with that AP reach)
Time constant (Reciprocal of the Time Constant)
Local-circuit current intensity (max dV/dt)
Threshold potential
Temperature
Myelination

Question 8

11. steps in modelling conduction

Answer 8

1. AP mechanism
2. Squid
   3.Voltage clamp
   4- Separate Na and K currents by changing bath
   5- Find membrane conductivity for Na and K from Ohms Law
   6- Model membrane conductivity using gating probabilities n, gk
3. Find constant voltage solution to the model in terms of n and tau
4. Fit model to g vs t to find alpha and Beta as functions of V
5. Model membrane currents and understand observations
6. Deduce membrane resistance, capacitance and cytoplasm resistance
7. Conduction velocity dependencies