A neurotransmitter is a chemical messenger that plays an important role in transmitting signals within the nervous system. It is produced by neurons and transported to synapses, where it is released into the synaptic cleft to communicate with other neurons or target cells. Neurotransmitters are responsible for various functions such as muscle contraction, gland secretion, and regulation of moods and behaviors. The action of neurotransmitters is usually brief, lasting only milliseconds before being removed from the synaptic cleft by reuptake or enzymatic degradation.