neurotransmittorn

Neurotransmittorn is a chemical messenger that transmits signals across a synapse between neurons and from neurons to effector cells. It is synthesized and stored in the presynaptic neuron and released into the synaptic cleft in response to an action potential, after a rise in intracellular calcium triggers the fusion of synaptic vesicles with the presynaptic membrane.

On the postsynaptic side, the neurotransmittorn binds to specific receptors, producing either excitatory or inhibitory effects. Ionotropic receptors open ligand-gated ion channels; metabotropic receptors activate second messenger pathways. The net effect depends on the receptor type and the ionic driving forces of the postsynaptic cell.

Neurotransmittorns are broadly categorized as small-molecule transmitters (such as acetylcholine, glutamate, GABA (gamma-aminobutyric acid), glycine, dopamine, norepinephrine, serotonin, and histamine) and neuropeptides (such as substance P and endorphins). There are additional signaling substances, including gaseous transmitters like nitric oxide, which can act as retrograde signals.

After release, neurotransmittorns are removed from the synaptic cleft by reuptake into the presynaptic neuron or neighboring glial cells, enzymatic degradation (for example acetylcholine by acetylcholinesterase), or diffusion. Reuptake and degradation terminate the signal and allow vesicles to be recycled.

Disruptions in neurotransmittor systems are linked to many disorders. Pharmacological agents often target these systems to modify mood, perception, movement, or arousal, such as SSRIs that increase serotonin signaling or acetylcholinesterase inhibitors that raise acetylcholine levels.