After finishing this chapter, students should be able to understand:
Chemical signals in the body are important for maintaining homeostasis. The two types of chemical signals are hormones and neurotransmitters.
Neurotransmitters act over brief time periods and very small distances because they are released into the synapse between neurons and are then rapidly cleared from the synapse.
Receptors are specialized structures that recognize neurotransmitter molecules and, when activated, cause a change in the electrical activity of the neuron.
The nervous system can be roughly divided into the central nervous system, the somatic system, and the autonomic system.
The autonomic system, with its sympathetic and parasympathetic branches, is important because so many psychoactive drugs also have autonomic influences on heart rate, blood pressure, and so on.
Specialized chemical pathways contain the important neurotransmitters dopamine, acetylcholine, norepinephrine, and serotonin.
The nigrostriatal dopamine system is damaged in Parkinson's disease, leading to muscular rigidity and tremors.
The mesolimbic dopamine system is thought by many to be a critical pathway for the dependence produced by many drugs.
The neurotransmitter GABA is inhibitory and is found in most parts of the brain.
The life cycle of a typical neurotransmitter chemical involves uptake of precursors, synthesis of the transmitter, storage in vesicles, release into the synapse, interaction with the receptor, reuptake into the releasing neuron, and metabolism by enzymes.
Psychoactive drugs act either by altering the availability of a neurotransmitter at the synapse or by directly interacting with a neurotransmitter receptor.
