neurotransmiterem

Neurotransmitters are chemical messengers that transmit signals between neurons and other cells in the nervous system. They are released from the presynaptic terminal in response to an action potential, diffuse across the synaptic cleft, and bind to receptors on the postsynaptic membrane, influencing the excitability of the receiving cell. Termination of signaling occurs through reuptake into the presynaptic neuron, enzymatic degradation, or diffusion away from the synapse.

Neurotransmitters can be broadly categorized into small molecules, peptides, and gases. Small-molecule transmitters include glutamate (the primary excitatory neurotransmitter in the central nervous system), GABA and glycine (major inhibitory transmitters), acetylcholine (important at neuromuscular junctions and some central synapses), and monoamines such as dopamine, norepinephrine, and serotonin. Neuropeptides, such as substance P and endorphins, modulate signaling with typically longer-lasting effects and often act as neuromodulators rather than direct fast transmitters. Gaseous transmitters, including nitric oxide and carbon monoxide, can act as retrograde signals that influence synaptic strength.

Receptors for neurotransmitters are of two main types: ligand-gated ion channels (ionotropic receptors) that produce rapid, short-lived responses, and G-protein–coupled receptors (metabotropic receptors) that initiate slower, longer-lasting intracellular cascades. The precise combination and balance of neurotransmitters and receptors determine the net effect on a target neuron or tissue, enabling complex modulation of mood, movement, perception, and learning.

Dysfunction of neurotransmitter systems is implicated in numerous conditions, including Alzheimer's disease (cholinergic loss), Parkinson's disease (dopaminergic deficit), depression (serotonin and norepinephrine alterations), and schizophrenia (dopamine and glutamate signaling abnormalities).