An American text-book of physiology . akes themore explicit form of the question whether cell-branches become continuousby secondary union. In mammals, man included, there is no good histo-logical evidence that such secondaryunion occurs in the central system,A close apj)roximation of the partsof two nerve-cells is alone to beseen. The means by which the cellsare brought close together are notalways the same. If the branchingof the neurons in the neighborhood ofthe dendrons of the large pyramidalcells is subject to the interpretationthat the impulses act across the smallintervals that separate
An American text-book of physiology . akes themore explicit form of the question whether cell-branches become continuousby secondary union. In mammals, man included, there is no good histo-logical evidence that such secondaryunion occurs in the central system,A close apj)roximation of the partsof two nerve-cells is alone to beseen. The means by which the cellsare brought close together are notalways the same. If the branchingof the neurons in the neighborhood ofthe dendrons of the large pyramidalcells is subject to the interpretationthat the impulses act across the smallintervals that separate these two struc-tures, then, when it is found that theneurons in some cases end in an en-closing basket or frame about thebodies of the cells of Purkinje, itwould be correct to infer that the ac-tion took place between the terminalsof the neuron and the bodij of the cellwhich they surround. If this infer-ence is correct, then the dendrons are not necessarily the sole pathways for theimpulses which affect a given cell (see Fig. 164).. Fig. 164.—Showing at the lower edge of the figurea series of basket-like terminations of neuronswhich surround the bodies of the great cells ofPurkinje in the cortex of the cerebellum (Ram6ny Cajal): C, cell-body; N, neurons; B, basket-liketerminations arising from cell C, and enclosing thecells of Purkinje. 644 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. Theories of the Passage of the Nerve-impulse.—Accej)tiug the viewtliat the nervous system is composed of discontinuous l)ut closely apjuoxi-mated cell-elements, it remains to explain how impulses arising within thelimits of one element are able to influence others. As an hypothesis, this may be assumed as dependent on chemical changesset up at the tips of the terminals and affecting the surrounding substance,which, thus affected, acts to stimulate the neighboring dendrons. As this isonly an hypothesis, it may be left with the statement that it seems to fit inlarge measure the group of facts which it
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Keywords: ., bookautho, bookcentury1800, bookdecade1890, booksubjectphysiology
