Volume 10

Twentieth century practice : an international encyclopedia of modern medical science / by leading authorities of Europe and America ; edited by Thomas L. Stedman.

Date:
1895-1903
Catalogue details

Licence: In copyright

Credit: Twentieth century practice : an international encyclopedia of modern medical science / by leading authorities of Europe and America ; edited by Thomas L. Stedman. Source: Wellcome Collection.

    38/880 (page 24)
    after leaving the cell; it can be followed as a continuous thread for a long distance. The teachings of neuroanatomists to-day are towards a tieatment of the ganglion cell with its axis-cylinder prolongation as an anatomical and functional entity, to which the name neuron (Waldeyer) is given. Almost all ganglion cells have but one axis-cylinder prolon- gation, although some axis-cylinder prolongations divide into two. The course of this prolongation is generally a long one, and it gives off in the mean time but few lateral branches, the so-called collaterals which course for a greater or lesser distance in pericellular baskets or network (Fig. 8). At its termination, which is always around certain individual or some nest of ganglion cells, it splits up into terminal end branches, technically known as terminal arborizations. The gan- glion cell has other prolongations than the one which is called the axis-cylinder prolongation; all these split up soon after their origin into a fine network, which are traceable only a short distance after their branching. These processes are known as protoplasmic pro- longations in contradistinction to axis-cylinder prolongations, or more commonly as dendrites. The terminal branchings of these dendrites as well as the terminal arborization of the nerve fibres are always free—that is, there is no continuity or confluence between them and the dendrites of other cells or of the terminal arborizations of other axis-cylinder prolongations. Their connection is by simple contact only. It was formerly thought, and is still by some (Golgi, Daziel) that the ramifications and especially the end arborizations of the nerve processes form anastomoses with, those of the other nerve ele- ments, thus forming actual networks through which the impulse could be carried over from one nerve element to the other. It is almost certain, however, that each nerve element with all of its rami- fications preserves an individuality and that the transmission of a nervous impulse from one element to another occurs without anasto- mosis of the anatomical elements. Contact or close proximity of the ramifications of one nerve element with that of the other sub- serves this function. Neurons are divided first of all, according to their function, into motor and sensory. Each of these is divided into a primary or cen- tral neuron and a secondary or peripheral neuron. A primary motor neuron consists of a ganglion cell in the motor areas of the brain (ascending frontal and ascending parietal convolutions) and its axis-cylinder prolongation, which extends to ganglion cells in the oblongata and cord around which cells the arborization of the axis cylinder takes place. This constitutes the corticonuclear division of the motor tract. A secondary or peripheral motor neuron is made up of a ganglion cell around which the arborization of the axis-cylin-