Sinapsii

Sinapsii (synapses) are specialized junctions through which neurons communicate with other neurons, muscle cells, or glandular cells. In the nervous system, the majority of intercellular signaling occurs at chemical synapses, while electrical synapses also exist in certain circuits. A chemical synapse typically consists of a presynaptic terminal containing neurotransmitter-filled synaptic vesicles, a synaptic cleft, and a postsynaptic membrane equipped with receptors. Electrical synapses comprise gap junction channels that permit direct ionic current flow between cells.

During neurotransmission, an action potential arriving at the presynaptic terminal opens voltage-gated calcium channels, allowing Ca2+ influx. This triggers vesicle fusion and release of neurotransmitter into the synaptic cleft. The transmitter diffuses across the cleft and binds to receptors on the postsynaptic membrane, causing ion channels to open or activating intracellular signaling pathways. The resulting change in the postsynaptic membrane potential can be excitatory (EPSP) or inhibitory (IPSP). Metabotropic receptors can produce slower, modulatory effects via second messenger systems, altering neuronal excitability and synaptic strength.

Synapses are dynamic and subject to plasticity. Repeated activity can strengthen synaptic connections (long-term potentiation) or weaken them (long-term depression), changes that accompany learning and memory. Structural changes, such as the growth or elimination of dendritic spines and synapse formation (synaptogenesis), also contribute to plasticity and circuit remodeling.

Impairment of synaptic function is linked to various neurological conditions, including neurodegenerative diseases, psychiatric disorders, and neuromuscular junction disorders. The study of sinapsii is central to understanding how the brain processes information and adapts to experience.