neurotrasmiter

A neurotransmitter is a chemical messenger that transmits signals across synapses between neurons and from neurons to other excitable cells. Most neurotransmitters are synthesized in the presynaptic neuron and stored in synaptic vesicles. When an action potential reaches the axon terminal, calcium influx triggers vesicle fusion and release into the synaptic cleft.

After release, neurotransmitters bind to receptors on the postsynaptic cell. Receptors are broadly categorized as ionotropic (ligand-gated ion channels) that produce rapid changes in membrane potential, and metabotropic (g protein-coupled) that initiate slower but longer-lasting effects through second messengers. The signaling is terminated by reuptake into the presynaptic neuron or nearby glial cells, enzymatic degradation, or diffusion away from the synapse.

Neurotransmitters can be grouped into two main classes. Small molecule transmitters include glutamate, which typically acts as an excitatory signal; GABA and glycine, which are primarily inhibitory; and acetylcholine, dopamine, norepinephrine, and serotonin, which regulate diverse functions such as movement, mood, attention, and arousal. Neuropeptides, such as substance P, enkephalins, oxytocin, and vasopressin, often modulate network activity and can have widespread, longer-lasting effects.

Neurotransmitter systems underlie sensory processing, motor control, cognition, emotion, and autonomic regulation. Disruptions in neurotransmitter signaling are linked to many neurological and psychiatric disorders, including epilepsy, Parkinson’s disease, depression, and schizophrenia. Treatments frequently target synthesis, receptor activity, or reuptake to restore balanced signaling.