Question

For each of these multiple choice questions. I not only want your answer, but I also want an explanation for why you as a group think that the answer that you have chosen is the right answer. This should include why the other answers are incorrect too. Let's spend a moment on membrane potentials in a typical neuron (ie, the squid giant axon). Which of the following statements is NOT true?

Answer 1

Answer: a & e & f

1. Statement ‘a’ is False- At 0mV, there will not be any rise in sodium and potassium currents at rest in neuron with voltage clamp technique.

Reason: We have to inject depolarizing current across an excitable membrane may be sufficient to generate an action potential (also called an 'impulse' or 'spike') in voltage clamp techque. Normal resting potential is -65mV approximately.

Reasons why other statements are correct:

Then the sodium channels are blocked with tetrodotoxin, thereby less inward current slow out ward current and the measurement represents only the potassium current. Thereafter, the tetrodotoxin is flushed away, and a control measurement is made. You can see in the image with volateclamp+tetradotoxin (TTX)

out out Control Control out out in 300 nM TTX 6 mM TEA 30 Time [ms] 0 5 0 0 20 Time [ms]

20 Depolarization [mV] 109 100 18 76 14-63 12- 51 38 32 10x GN 10 mV] 26 19 8 Time [ms] 10

As per Hodgkin-Huxley theory, behavior of sodium conductance in voltage clamp experiments. Here the clamp voltage is expressed as a change from the resting value (in [mV]). Note that the change in sodium conductance is small for subthreshold depolarizations but increases greatly for transthreshold depolarization ( Vm = 26 mV). There by E_Na and G_Na is gerater than 0. Membrane reaches threshold only when the sodium channels open.