The plan of the central nervous system : a thesis for the degree of Doctor of Medicine in the University of Cambridge / by Alex. Hill.

  • Hill, Alex, 1856-1929.
Date:
1885
Catalogue details

Licence: Public Domain Mark

Credit: The plan of the central nervous system : a thesis for the degree of Doctor of Medicine in the University of Cambridge / by Alex. Hill. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    opinion as to their importance would be formed if the cord of a fish were first examined; in the fish the filaments of the meshwork are coarse and conspicuous, the cells little more than nuclei situate at their meeting points. Indeed it would appear that the course taken by the disturbance of nerve force which constitutes an impulse, depends upon the resistance in the matrix felt-work, not iipon that in the cells. An im.pulse travelling up a certain sensory fibre reaches the cell in the spinal cord with which that fibre is in connection ; from this it travels, if the road be open, up the sensory tract, either by means of felt-work, or of long or short commissural fibres, be- cause the resistance is less in this direction than it is across from sensory to motor cell. If however the aesthesodic route be blocked, transference across to a motor cell of its own meta- mer occurs, and a simple reflex action is the result. We can only describe the functions of the cell in this connection as distributive. It is the shunt at which meet many lines of con- duction, and through which alone therefore can a redistribution of the impulse occur; while the course which the impulse now takes depends not upon the resistance within the cell but in that in the various lines of conduction which diverge from it. I should regard the distributive function of the cell in this instance as re-directive. A simpler arrangement appears how- ever to obtain in the case of the ganglion cells of the retina. Here the fibres connecting the rods and cones with the ganglion cells are much more numerous than those connecting the gan- glion cells with the primary optic centre, and the object of the interposition of the cells is to condense, in other woixls, the distribution is associative. Many instances occur to us of an arrangement the reverse of this; compare for instance the single process reaching each cell of Purkiuje in the cerebellum (cells not wholly unlike the ganglion cells of the retina in ex- ternal appearance) with the number of processes leaving it. In this case the distribution is dissociative, and probably the func- tion of nerve cells throughout the system is to a very large extent that of increasing the number of fibres towards the peri- phery. Nerve cells may be regarded as the nodal points of the nerve-network.