synapsí

The synapsí, or synapse, is the junction where one neuron communicates with another neuron or with a non-neuronal cell. Most signals in the brain are transferred at chemical synapses, while a subset uses electrical coupling.

In a typical chemical synapse, the presynaptic terminal contains synaptic vesicles loaded with neurotransmitters. The synaptic cleft separates the presynaptic and postsynaptic membranes. The postsynaptic membrane bears receptors that bind neurotransmitters, transforming chemical signals into electrical changes in the target cell. The structure is often supported by astrocytes in a tripartite synapse.

Electrical synapses rely on gap junctions formed by connexin proteins that permit ions to flow directly between cells, enabling rapid and bidirectional signaling. They are less common in the mature mammalian CNS but important in certain circuits.

Transmission sequence: an arriving action potential opens voltage-gated Ca2+ channels, triggering neurotransmitter release via exocytosis. Released molecules diffuse across the cleft and bind receptors, causing excitatory or inhibitory postsynaptic potentials. The process is rapid, variable in strength, and subject to modulation.

Plasticity: synapses can strengthen or weaken over time. Short-term plasticity includes facilitation and depression; long-term changes such as LTP and LTD contribute to learning and memory. Synaptogenesis and synaptic pruning shape neural networks during development and experience.

Clinical relevance: synapse dysfunction is linked to neurological and psychiatric disorders; understanding synapses informs treatments and pharmacology.