Neurotranszmitter

A neurotransmitter is a chemical messenger that transmits signals across a synapse from a neuron to another neuron, a muscle cell, or a gland cell. When an action potential reaches the presynaptic terminal, the neurotransmitter is released into the synaptic cleft, binds to receptors on the postsynaptic cell, and induces a response that may be excitation, inhibition, or modulation of signaling. Neurotransmitters are typically cleared rapidly from the synapse by reuptake into the presynaptic neuron, enzymatic degradation, or diffusion away from the synapse.

Major classes include small-molecule transmitters such as acetylcholine, glutamate, gamma-aminobutyric acid (GABA), and glycine; monoamines such as dopamine, norepinephrine, epinephrine, serotonin, and histamine; and neuropeptides such as substance P, enkephalins, and oxytocin. In addition, certain gases like nitric oxide and carbon monoxide can act as unconventional neurotransmitters. These chemicals can function as primary transmitters or as co-transmitters that modulate signaling alongside other transmitters.

Synthesis and storage occur in the nerve terminal. Acetylcholine is made by choline acetyltransferase; amino acid transmitters are produced from common metabolic precursors; monoamines are synthesized through specific enzymatic steps. After synthesis, transmitters are packaged into synaptic vesicles and released in response to calcium influx.

Receptors on the postsynaptic membrane are of two main types: ligand-gated ion channels (ionotropic) and G protein-coupled receptors (metabotropic). Receptor binding can produce fast postsynaptic potentials or slower signaling cascades, and effects are shaped by receptor distribution, transporter activity, and enzymatic degradation. Disruptions in neurotransmission are linked to many conditions, including Parkinson’s disease, depression, epilepsy, and Alzheimer’s disease, and many therapeutic drugs act by altering neurotransmitter systems.