Alkaloid

Many alkaloids act by blocking or intensifying the actions of neurotransmitters, chemicals released by nerve cells in response to an electrical impulse called a neural signal. Neurotransmitters diffuse into neighboring cells where they produce an appropriate response, such as an electrical impulse, in another nerve cell or contraction in a muscle cell.

Each nerve cell produces only one type of neurotransmitter; acetylcholine and norepinephrine are the most common. Cells may respond to more than one type of neurotransmitter, however, and the response to each type may be different.