neurotransmitor

Neurotransmitter, sometimes misspelled as neurotransmitor, is a chemical messenger that transmits signals between neurons or between neurons and other cells at synapses. Most neurons store neurotransmitters in synaptic vesicles and release them in response to an action potential, triggered by calcium influx through voltage-gated channels. The released molecules diffuse across the synaptic cleft and bind to receptors on the postsynaptic cell, producing excitatory or inhibitory effects that shape neural circuits. The action is terminated by reuptake into presynaptic terminals, enzymatic degradation, or diffusion away from the synapse.

Major classes include small-molecule transmitters such as acetylcholine; amino acids such as glutamate, GABA, and glycine; monoamines such as dopamine, norepinephrine, and serotonin; purinergic transmitters like ATP; and neuropeptides such as substance P. Gasotransmitters, notably nitric oxide, diffuse directly without conventional vesicular release or receptors.

Receptors are broadly of two types: ionotropic receptors that form ion channels for rapid responses, and metabotropic receptors that activate intracellular signaling cascades. Termination of signaling commonly involves neurotransmitter reuptake by specific transporter proteins (e.g., SERT, DAT, NET) or enzymatic degradation (e.g., acetylcholinesterase for acetylcholine).

Neurotransmitters operate throughout the nervous system, mediating reflexes, sensation, movement, learning, and mood. Their effects depend on receptor type and cellular context; the same transmitter can be excitatory in one location and inhibitory in another.

Disruptions in neurotransmitter systems are linked to many disorders, including Parkinson's disease (dopamine depletion), Alzheimer's disease (glutamatergic and cholinergic dysfunction), depression (serotonin and norepinephrine), and schizophrenia (dopaminergic and glutamatergic imbalance).