Outline how nerve impulses are transmitted along a nerve fibre.

a. (sodium channels/voltage-gated channels open and) Na+ diffuse into neuron (down concentration gradient);
b. inside of neuron becomes positive compared to outside / potential is reversed / depolarization;
c. wave of depolarization moves (down the membrane);
d. (potassium channels open and) K+ diffuse out (down concentration gradient);
e. inside becomes negative compared with outside / potential across membrane restored / repolarization;
f. active transport of K+ (into neuron) and Na+ (out of neuron) restores resting potential;

Many low to medium scripts had answers which tackled this question from an anatomical or cytological rather than neurophysio point of view. There was confusion about the meaning of “along a nerve fibre.” Many thought that a “fibre” was more than a single neuron. This lead to outlines of a neural pathway rather than the changes that occur within a single neuron as an impulse passes. Several candidates outlined synaptic transmission. This question could have been set for more marks. Consequently, the strongest candidates often earned more marks than the maximum that could be awarded, while most earned no marks.