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.

Question
Is the pre-synaptic or the post-synaptic neuron damaged? Explain your rationale in detail (in other words, detail how you came to your conclusion). You’re going to have to really think about this one. It’s not something you can look up in the text. You will need to use what you have learned about the autonomic nervous system and some critical thinking to arrive at the answer.