A patient has been diagnosed with Horner’s syndrome, a disorder that is due to damage of sympathetic nerves that travel to the eye. It occurs unilaterally and results in extreme pupil constriction and reduced sweating on the affected side. The young resident who diagnosed the condition is an autonomics freak and is eager to determine if it is the pre-ganglionic nerve or the post-ganglionic nerve that is damaged. For his determination, he injects acetylcholine, which caused sweating on the affected side, but he sees no change in pupil size. He then injects norepinephrine and the pupil dilates, but no sweating occurs.

Is the pre-synaptic or the post-synaptic neuron damaged?