Question

A new student in your lab is trying to test whether injection of FGF2 into the lesioned spinal cord led to functional regeneration of afferents across the lesion site. The student is stimulating the lateral corticospinal tract with two depolarizing pulses that are 1 millisecond apart. However, only the first stimulus results in an action potential being generated. What is the best explanation for the failure to generate an action potential with the second stimulus?

a. All the external sodium has entered the neuron and must be pumped out before the nerve can fire again.

b. The voltage dependent sodium channels have inactivated and cannot be opened until the refractory period has ended.

c. Due to a temporary increase in Cl- conductance, the neuron cannot be depolarized

d. Corticospinal neurons are glutamatergic, thus, they do not utilize sodium to conduct action

potentials

e. Corticospinal neurons exhibit a high degree of paired pulse depression

Answer 1

Option b-The voltage dependent sodium channels have inactivated and cannot be opened until the refractory period has ended.

Refractive period is the Time period in which a second stimulus following 1st Stimulus donot produce an Action Potential.

There is Absolute Refractive Period And Relative Refractory period.

Immediately following the 1st Stimulus cuasing Action potential in the neuron ,there is ABSOLUTE REFRACTORY PERIOD.In this Period,Action potential cannot be stimulated whatever the strength of the stimulus be.This is due to the inactivation of Na+ Channels(Depolarisation occur when this Na+ channel is opened allowing Entry of Na+ inside)

Following Absolute Refractory Period there is RELATIVE REFRACTORY PERIOD.Here also,Mostly The second stimulus cannot initiate action potential.This is Because of increase in the threshold for Opening of Na+ Channel.