Transmitterne

Transmitterne, in Danish and Norwegian, refers to neurotransmitters—the chemical messengers that carry signals across synapses between nerve cells and from nerves to muscles or glands. They operate at chemical synapses and, in some systems, at neuromuscular junctions, enabling rapid and targeted communication within the nervous system. They can also function as neuromodulators or neurohormones in broader signaling networks.

Major categories include small-molecule transmitters and neuropeptides. Small-molecule transmitters include glutamate (excitatory in the CNS), GABA and glycine (inhibitory), acetylcholine, and biogenic amines such as dopamine, norepinephrine, serotonin, and histamine. Neuropeptides, such as substance P, endorphins, vasopressin, oxytocin, and neuropeptide Y, typically modulate signaling over longer timescales. Some diffuse signaling molecules, known as gasotransmitters (for example nitric oxide), act differently from conventional synaptic transmitters by diffusing more freely between cells.

Synthesis, storage, and release follow a common sequence. Transmitters are synthesized in the presynaptic neuron and loaded into synaptic vesicles. Upon an action potential, voltage-gated calcium channels open, triggering vesicle fusion and release into the synaptic cleft. They bind to postsynaptic receptors, which can be ionotropic (direct, fast effects) or metabotropic (indirect, modulatory, longer-lasting effects).

Termination mechanisms include reuptake into the presynaptic neuron or neighboring glial cells, enzymatic degradation (as with acetylcholine by acetylcholinesterase), and, for some transmitters, diffusion away from the synapse.

Transmitterne are essential for perception, movement, learning, memory, mood, and autonomic regulation. Dysfunctions in transmitter systems are linked to diseases such as Parkinson's disease, Alzheimer's disease, depression, anxiety disorders, epilepsy, and schizophrenia. Therapeutic agents often target these pathways, including SSRIs, MAO inhibitors, acetylcholinesterase inhibitors, and various receptor modulators. History notes Otto Loewi's 1921 demonstration of chemical transmission.