| Neurotransmitter | Function | Examples of Malfunctions |
| Acetylcholine (ACh) | Enables muscle action, learning, and memory | With Alzheimer’s disease, ACh-producing neurons deteriorate. |
| Dopamine | Influences movement, learning, attention, and emotion | Oversupply linked to schizophrenia. Undersupply linked to tremors and decreased mobility in Parkinson’s disease. |
| Serotonin | Affects mood, hunger, sleep, and arousal | Undersupply linked to depression. Some drugs that raise serotonin levels are used to treat depression. |
| Norepinephrine | Helps control alertness and arousal | Undersupply can depress mood. |
| GABA (gamma-aminobutyric acid) | A major inhibitory –neurotransmitter | Undersupply linked to seizures, tremors, and insomnia. |
| Glutamate | A major excitatory neurotransmitter; involved in memory | Oversupply can overstimulate brain, producing migraines or seizures (which is why some people avoid MSG, monosodium glutamate, in food). |
| Endorphins | Neurotransmitters that influence the perception of pain or pleasure | Oversupply with opiate drugs can suppress the body’s natural endorphin supply. |