Synapse

SYNAPSIS, or synapse (from Greek synapsis—connection), is the anatomical and physiological contact between individual neurons. In lower invertebrates, nerve cells are in continuous connection with one another through protoplasmic processes that pass directly from one cell into another. In higher invertebrates and all vertebrates, the nervous system is represented not as such a network of directly connected cells, but as separate neurons: the cells do not have a continuous connection with each other, but merely touch each other with their processes. The site of such a combination between neurons is designated by the term S., proposed by Sherrington (1906). The following forms of synaptic combinations are distinguished: 1. Axosomatic S., in which the terminal branches of the axon of one neuron entwine the cell of another neuron; an example of such a S. is the entwinement of the body of Purkinje cells by the terminal branches of the axons of basket cells of the cerebellum; axosomatic synapses are also observed in some other areas of the central nervous system, as well as in the sympathetic system of the intestine. 2. Axodendritic S., in which communication between neurons occurs by way of contact between the branches of the axon of one neuron and the dendrite of another; in this case, two varieties of this form of S. are distinguished: primary axodendritic S., in which there is an enveloping of dendritic endings by axonal endings (examples of this can be the climbing fibers of the cerebellum, entwining with their endings the terminal branches of the dendrites of Purkinje cells in the molecular layer of the cerebellar cortex), and terminal axodendritic S., in which the axon and dendrite come into contact by the distal endings of their branches, an example of which is the combination between mossy fibers and the dendrites of granule cells in the granular layer of the cerebellum, as well as in the motor region of the cerebral cortex. The physiological role of the synapse consists in the integrative function, i.e., in the function of combining impulses, stimulating them, and inhibiting them. The synapse is also ascribed the function of polarization of the combining neurons, i.e., directing impulses from the axon of one neuron to the dendrite of another (see Reflexes).

M. Astvatsaturov. [Note on cell nucleus / germ cells context in original OCR fragment: ...vits] express doubts about the coincidence of the physiological significance of S. observed in male and female germ cells, based on the large interval of time that elapses in oocytes between the end of S. and the beginning of the reduction division itself. American and English authors introduce a new terminology for the described phenomenon—meiotic phenomena, meiosis; the stage of the synaptic knot is designated by them as synezesis. S. Zalkind.