Neurotransmitia

Neurotransmitia are chemical messengers that mediate communication between neurons and their target cells at synapses. They are released from the presynaptic terminal in response to an action potential and travel across the synaptic cleft to bind to receptors on the postsynaptic membrane, thereby altering the electrical or chemical state of the target cell.

Two broad groups are commonly recognized: small molecule transmitters and neuropeptides. Small molecule transmitters include acetylcholine, glutamate, gamma-aminobutyric acid (GABA), glycine, and biogenic amines such as dopamine, norepinephrine, serotonin, and histamine. Neuropeptides, such as substance P, endorphins, and neurotensin, are often released with longer-lasting activity and can modulate neural networks.

Neurotransmitia are stored in synaptic vesicles at the presynaptic terminal. An arriving action potential opens voltage-gated calcium channels, Ca2+ influx triggers vesicle fusion, and transmitters are released by exocytosis. They bind to receptors on the postsynaptic cell, producing fast excitatory or inhibitory effects via ionotropic receptors or slower modulatory effects via metabotropic receptors. The resulting signal is typically brief and highly localized.

Termination mechanisms limit the duration of signaling. Neurotransmitia are removed by reuptake into the presynaptic neuron, enzymatic degradation (for example acetylcholinesterase acting on acetylcholine), or diffusion away from the synapse. Receptor density and signaling pathways can undergo plastic changes with activity, contributing to learning and adaptation.

Neurotransmitia underpin neural circuits for sensation, movement, learning, memory, mood, and autonomic control. Dysregulation is linked to numerous conditions, including Parkinson disease, depression, anxiety, schizophrenia, and epilepsy. Pharmacological agents often target neurotransmitia or their receptors to treat these disorders.