[Interneuronal synapses with electrical and chemical mechanisms of transmission and the evolution of the central nervous system].

It becomes increasingly evident that not only chemical but also electrotonic synapses are characteristic feature of the vertebrate brain. Experiments carried out on the isolated perfused central nervous system of lampreys and frogs have shown that in cyclostomes spinal motoneurons receive at least 4 different electrotonic inputs: from giant reticulospinal axons, from smaller descending fibers intrinsic to the cord, from primary afferents and ventral roots. In amphibian motoneurons it is possible to identify 3 electrotonically mediated monosynaptic actions: from primary afferents, recurrent, and reticulospinal. The exact mode of transmission of monosynaptic excitation 1a and supraspinal actions in mammals remains to be elucidated. The trends of evolutionary development of synaptic transmissional processes and synaptic organization in vertebrate nervous system are discussed.