Re: what makes you salivate?

ACETYLCHOLINE!

Well. let's take a step back..

Acetylcholine is a neurotranmitter that comes form nerve endings in the salivary gland. The nerve endings secrete it when they receive stimulation from "higher up." The endings contact cells in the salivary gland, alerting them to release their contents into the mouth (saliva).

Still not enough?

The nerve endings in the salivary gland belong to a part of the nervous system referred to as the Autonomic Nervous System. The ANS has two subdivisions, the parasympathetic nervous system, and its counterpart, the sympathetic nervous system. Each system has inverse, but equally important functions.

• Parasympathetic: You should think of your parasympathetic nervous system as the wiring that handles basic "bodily functions." These functions include eating, digesting, and going to the bathroom. The primary messenger of the parasympathetic nervous system is a molecule called acetylcholine.
• Sympathetic: In contrast, the sympathetic nervous system handles "flight/fright" reactions - things that help you survive in the event of danger or other stressful situations. Stimulation by the sympathetic nervous system increases the heart rate, blood pressure, and causes the eyes to dilate (the better with which to see?). Nor-epinephrine (adrenalin) is the primary messenger of the sympathetic nervous system**.

If you want to take a further step back..

Nerve centers for both the sympathetic and parasympathetic systems live in the brain, and are integrally connected with other functional areas, including ones that process smells, tastes and images. Certain stimuli lead to parasympathetic signals that go to the salivary gland while others may lead to sympathetic output, or no output whatsoever..

So when you smell/see/taste a delicious apple pie, a combination of stimuli are received and processed by the brain. A smart brain realizes *IT'S TIME TO EAT*. Parasympathetic centers are stimulated (digestion) and send output along parasympathetic nerve fibers that innervate the salivary glands. The fibers release *acetylcholine* (not epinephrine) which causes the glands to secrete saliva, and viola! you salivate.

Note: I am oversimplifying somewhat to keep things simple... Some elements of the sympathetic nervous system (certain "preganglionic fibers") do use acetylcholine as a neurotransmitter.