A neurotransmitter is a chemical messenger that transmits signals across synapses between neurons or from neurons to other types of cells, such as muscle or gland cells. They play a pivotal role in neurocommunication, influencing a variety of physiological processes, from muscle contractions to mood regulation. Common neurotransmitters include serotonin, dopamine, and acetylcholine, each with specific functions in the nervous system. Proper neurotransmitter balance is crucial for overall mental and physical health, with imbalances often linked to various disorders, including schizophrenia and depression.