sinapses

Sinapses, commonly called synapses in English, are junctions where neurons communicate with other neurons or with non-neuronal cells such as muscles or glands. They can be chemical or electrical. Chemical synapses are the most widespread, using neurotransmitters to convey signals across a small gap, while electrical synapses rely on direct electrical coupling via gap junctions for rapid, bidirectional transmission.

A chemical synapse consists of a presynaptic terminal packed with synaptic vesicles, a specialized active zone for vesicle fusion, a synaptic cleft, and a postsynaptic membrane with receptors. An arriving action potential triggers opening of voltage-gated calcium channels, causing vesicles to fuse with the presynaptic membrane and release neurotransmitter. The transmitter diffuses across the cleft and binds to receptors on the postsynaptic cell, opening ion channels or modulating other signaling pathways to generate excitatory or inhibitory postsynaptic potentials.

Electrical synapses connect adjacent cells through gap junction channels formed by connexins in vertebrates or innexins in invertebrates. These channels permit direct passage of ions, producing fast, usually bidirectional electrical signaling with less flexibility than chemical synapses.

Synapses are plastic; their strength can change with activity. Short-term changes include facilitation and depression, while long-term changes such as long-term potentiation and long-term depression are associated with learning and memory. Plasticity is influenced by neurotransmitter systems, receptor composition, intracellular signaling, and structural remodeling.

During development, synapses form in a process called synaptogenesis and are later refined through pruning. Proper synaptic function is essential for sensation, movement, cognition, and behavior. Abnormal synaptic transmission has been linked to various neurological and psychiatric conditions, making synapses a central focus of neuroscience research.