So far, researchers have discovered about 15–20 different neurotransmitters, and new ones are still being identified. The nervous system communicates accurately because there are so many neurotransmitters and because neurotransmitters work only at matching receptor sites. Different neurotransmitters do different things.
| Neurotransmitter | Major functions | Excess is associated with | Deficiency is associated with |
| Acetylcholine | Muscle movement, attention, arousal, memory, emotion | Alzheimer’s disease | |
| Dopamine | Voluntary movement, learning, memory, emotion | Schizophrenia | Parkinsonism |
| Serotonin | Sleep, wakefulness, appetite, mood, aggression, impulsivity, sensory perception, temperature regulation, pain suppression | Depression | |
| Endorphins | Pain relief, pleasure | ||
| Norepinephrine | Learning, memory, dreaming, awakening, emotion, stress-related increase in heart rate, stress-related slowing of digestive processes | Depression | |
| GABA | Main inhibitory neurotransmitter in the brain | ||
| Glutamate | Main excitatory neurotransmitter in the brain | Multiple sclerosis |
Agonists are chemicals that mimic the action of a particular neurotransmitter. They bind to receptors and generate postsynaptic potentials.
Antagonists are chemicals that block the action of a particular neurotransmitter. They bind to receptors but can’t produce postsynaptic potentials. Because they occupy the receptor site, they prevent neurotransmitters from acting.
