Consider the following scenario and then answer the question in detail: A patien

Question

Consider the following scenario and then answer the question in detail:

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?

Explanation / Answer

Lets understand Horner’s syndrome first. This is happens when group of nerves known as the sympathetic trunk is damaged in facial area and eye. As it mentioned, signs will be extreme pupil constriction and reduced sweating on the affected side.

The case mentioned about young resident in the question, both pre and post synaptic neurons are damaged.  Because he has preganglionic (Pre synaptic) lesions that releases acetylcholine, he has reduced sweating. When he injects Acetyl choline it caused sweating. And he also has postganglionic (post synaptic) lesions, because of which norepinephrine release is stopped and hence results in extreme pupil constriction. When he injects norepinephrine, the pupil dilates. So, we can easily understand from this, his pre-synaptic and the post-synaptic neurons are damaged. Due to which acetylcholine injection is producing only sweating and norepinephrine injection is producing only pupil dilation.

That proves he needs to inject both acetylcholine & norepinephrine to see sweating and pupil dilation.

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