sinaps

Sinaps, or synapse, is the junction through which a neuron communicates with another neuron or with an effector cell such as a muscle or gland. In most synapses in vertebrates, communication is chemical, whereas electrical synapses use direct currents through gap junctions. A typical chemical synapse comprises a presynaptic terminal at the end of an axon, a synaptic cleft, and a postsynaptic membrane on the receiving cell. Presynaptic terminals contain synaptic vesicles filled with neurotransmitters; the arrival of an action potential opens voltage-gated calcium channels, triggering vesicle fusion and release of neurotransmitters into the cleft. The neurotransmitters diffuse across the cleft and bind to receptors on the postsynaptic membrane, producing excitatory or inhibitory postsynaptic potentials (EPSPs or IPSPs). Signal termination occurs via neurotransmitter reuptake, enzymatic degradation, or diffusion away from the synapse.

Electrical synapses use gap junctions that allow ions to pass directly between cells, enabling fast, bidirectional transmission and synchronization of neural activity.

Synaptic strength can change with activity, a phenomenon known as synaptic plasticity. Long-term potentiation (LTP) and long-term depression (LTD) are cellular mechanisms underlying learning and memory. The efficient operation of synapses depends on a wider cellular context, including glial cells at the tripartite synapse.

Major classical neurotransmitters include acetylcholine at neuromuscular junctions; gamma-aminobutyric acid (GABA) and glutamate are dominant in the central nervous system, mediating inhibition and excitation respectively.