Question

8. Consider a neuron whose resting potential is -60 mV, and the EK = -100 mV and the ENa = +40 mV. a) What is the driving force for Na+, and what is the driving force for K+ at the resting potential? Just give a number, don’t describe what a driving force is in words. b) What is the relative resistance of the cell membrane for sodium and potassium (i.e. how many times greater or less than the RK must the RNa be? N.B. resistance not permeability!) Just give a number, no words. c) A neurotransmitter-gated channel on this cell when opened has a synaptic reversal potential of -120 mV. Is it possible that the ion that flows through this channel is positively-charged? Give a yes or no answer, then briefly explain.

Answer 1

(a) The driving force of Na+ at the resting potential is -100mV.

The driving force of K+ at the resting potential is +40mV.

(b) The relative resistance of the cell membrane for sodium and potassium is 2.5, i.e., RNa is 2.5 times greater than the RK.

(c) No. Synaptic reversal potential is the state when neurotransmitters cause no net current flow of ions through that neurotransmitter-gated channel at this stage.

We know that,

Driving force (DF)= Vm-VE,

where, Vm is membrane potential and VE is equilibrium potential. In single ion system, Veq is referred to as reversal potential.

and, Current flow, I= g(Vm-VE)

When the membrane potential is equal to reversal potential, Vm-VE becomes zero.

That means, driving force also becomes zero. As a result, no ions movement occurs through the channels.