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?

                                                        water

a colorless, transparent, odorless, tasteless liquid that forms the seas, lakes, rivers, and rain and is the basis of the fluids of living organisms.

                                                        halon  

any of a number of unreactive gaseous compounds of carbon with bromine and other halogens, used in fire extinguishers, but now known to damage the ozone layer.

                                                  dry chemical

extinguishing agent used on class a, class b, and class c fires.

                                                  carbon dioxide

a colorless, odorless gas produced by burning carbon and organic compounds and by respiration. it is naturally present in air (about 0.03 percent) and is absorbed by plants in photosynthesis.