Nerve Endings

What bodily changes cause us to have a dry throat when we're nervous ?

When you're nerve-ridden during public speaking. the body is set into the fight or flight state. This is caused by an activation of the autonomic nervous system.

The nerves are selectively activated, depending on how important they are for response. Because eating is not considered to be vital at this time. You just want to get the heck out of there. The nerves that control the salivary glands are suppressed, so your mouth dries up. your pupils dilate and the blood vessels to your muscles and heart widen to get blood to the most important organs for whatever action is necessary.

In a tense or dangerous situation, your body shuts down all unnecessary functions, including the digestive system. your salivary glands are part of it. You don't need to digest your last meal if a lion is trying to make you his next. This is also where " butterflies in the stomach" comes from.