Synaps

Synaps, or synapse in English, is the functional junction between two neurons or between a neuron and another cell type. It enables electrical or chemical signaling across the nervous system. A typical chemical synapse comprises a presynaptic terminal containing synaptic vesicles filled with neurotransmitters, a synaptic cleft about 20–40 nanometers wide, and a postsynaptic membrane with neurotransmitter receptors. An electrical synapse uses gap junctions that permit direct ionic current flow.

Transmission occurs when an action potential arrives at the presynaptic terminal, opening voltage-gated calcium channels. Calcium influx triggers vesicle fusion with the membrane and release of neurotransmitters into the cleft. Neurotransmitters bind to receptors on the postsynaptic membrane, producing excitatory or inhibitory postsynaptic potentials. Termination of the signal occurs through reuptake, enzymatic breakdown, or diffusion.

Types: excitatory synapses (commonly using glutamate) raise likelihood of firing; inhibitory synapses (GABA, glycine) suppress activity. Receptors are classified as ionotropic (ligand-gated ion channels) or metabotropic (G-protein-coupled).

Plasticity: synapses change strength with activity, underpinning learning and memory via short-term plasticity and long-term potentiation/depression. Developmentally, synaptogenesis forms networks; pruning refines them.

Clinical relevance: synaptic dysfunction is implicated in many disorders, including Alzheimer's disease, schizophrenia, and autism. Many drugs modulate synaptic transmission, such as cholinesterase inhibitors, NMDA receptor modulators, and various neurotransmitter reuptake inhibitors.