synapse


synapse

Site of transmission of electric nerve impulses between two nerve cells or between a nerve cell and a gland or muscle cell. At chemical synapses, impulses are transmitted across microscopic spaces via chemical substances called neurotransmitters. In electric synapses, direct communication between nerve cells whose membranes are fused is possible because ions flow between the cells through channels. Electric synapses are found mainly in invertebrates and lower vertebrates; they transmit messages faster than chemical synapses. Chemical transmission seems to have evolved in large, complex vertebrate nervous systems, in which multiple messages must be transmitted over long distances.

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