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Intro to Neuroscience

  • Thread starter Wek
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Wek

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I need a little help with this assignment from my neuroscience class. I have tried to answer them but I'll like to know if my reasoning is right or wrong. I had to use the Neurons in Action software at school for some simulations but I think most of the questions could be answered without it.

First problem:
1. Using the plain bilayer membrane circuit and the default settings available in the membrane tutorial perform the following experiment:
a) Bring the capacitive Current vs Time graph. Under membrane parameters, change the membrane capacitance (microFarad/cm2) to the following values: 1, 2, 5, 10 and 100. Generate a plot of the rate of change of Vm as a function of capacitance. What kind of function describes the relationship between these variables?
By changing the membrane capacitance to values of 1, 2, 5, 10 and 100 (microFarad/cm2), the Vm across the membreane would decrease as the membrane capacitance increases. This due to the fact that the membrane's ability to hold a charge is increased and the electrical charge across the membrane is lowered.

b) Add the leak channels and repeat the experiment described in panel a. Can you explain what happens to the time constant of this circuit? Can you find an example in biology where the effective capacitance may increase several-fold from the canonical value of 1 microFarad/cm2? Explain.
By adding the leak channels to the bilayer membrane, the electrical current "decays" faster and the time constant is larger, making the speed of responses slow. No idea about an example, any help with this part would be appreciated.

c) Add HH channels and repeat the experiment. What happens to the capacitive current density between conditions b and c? What happens to the membrane threshold? Set the membrane capacitance to a value of 10 microFarad/cm2 , before you run the simulation, increase the density of Na and K channels by tenfold. Can you explain what happens to the membrane potential?
By adding the HH pump, the capacitve current density increases. The membreane threshold decreases. When the membrane capacitance has a value of 10 microFarad/cm^2 and the density of Na and K channels increased by tenfold, there is no change since everything increased by tenfold. Definetely not sure if this is right or not.

2. You may find the equilibrium potentials tutorial useful to answer the following problem: A recent study described the following concentration values (in mM) for the giant cell of the sea snail Aplysia.
[K+]in = 175 [Na+]in = 35 [Cl-]in = 60
[K+]out = 8 [Na+]out = 345 [Cl-]out = 335
and at rest, PK : PNa : PCl = 1 : 0.005 : 0.45
a) What is Vrest as predicted by the Goldman equation?
b) What would be the effect of a tenfold increase in the external K+ concentration on the resting potential?
c) The resting membrane conductances have been measured in this cell to be: gK = 0.57 microS; gNa = 0.11 microS; and gCl =0.32 microS. What is the resting potential of this cell predicted by the parallel conductance model? Remember the following equation:
Vrest = (gKEK + gNaENa + gClECl)/(gK + gNa + gCl)
a) Using the Goldman equation, the Vrest is -55 mV. Not sure how to calculate this Vrest.
b) It would increase the resting potential from -55 to -28 mV.
c) Using thi formula Vrest = (gKEK + gNaENa + gClECl)/(gK + gNa + gCl), the Vrest is -31.96 mV. I think a and c should match so one of them is worng, but sure which one.

I do not expect you guys to just tell me the anwer straight foward but any help would be appreciated. I have until wednesday to hand in this assignment and tuesday I'll try to redo the simulations with the software and double check.

Thanks
 

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