The involuntary nervous system / by Walter Holbrook Gaskell.

  • W. H. Gaskell
Date:
1916
Catalogue details

Licence: In copyright

Credit: The involuntary nervous system / by Walter Holbrook Gaskell. Source: Wellcome Collection.

    18/200 page 2
    the central nervous system unites the two; this I shall call throughout this book the “connector element When these three neurons belong to the same segment, the reflex may be termed a primary or segmental reflex; and the connector neurons concerned in such reflexes may be called primary connector neurons (Fig. 2, A). A connector neuron does not necessarily communicate directly with an excitor neuron but may only connect after a series of communications with other connector neurons, which thus form a series of relays between the receptor and excitor ele¬ ments. By means of this relay system of connector neurons the higher centres of the nervous system are brought into harmony with the segmental mechanism. The connector neurons of these relay systems may be called secondary connector neurons. The axon of a connector neuron cannot be called a motor or a sensory nerve fibre; I propose therefore to call it simply a con¬ nector fibre. When such connector fibres are grouped together in definite parts of the central nervous system, they are called tracts, which are designated as ascending or descending according to the position of the nerve cells, of which they are the axons. The great characteristic of these connector nerve fibres is the formation of collaterals, by means of which each nerve fibre connects with more than one neuron. In all cases the receptor neurons of the voluntary system are found in the posterior root ganglia both in the cranial and spinal regions, and the excitor neurons in the groups of nerve cells found in the central nervous system, which form the motor centres and give origin to the motor nerves of the voluntary muscles. These motor cell groups are not situated in the same position in all parts of the central nervous system. We have every reason to believe that the central nervous system of the verte¬ brate indicates a derivation from a segmentally arranged nervous system, such as is found in the higher forms of invertebrates, and the nerves which supply these segments form a succession of segmental nerves, which commence just posterior to the infundi¬ bulum and form a great group of nerves extending to the end of the body. They may therefore be termed infra-infundibular, in contradistinction to the nerves of special sense, olfactory and optic, which arise from the supra-infundibular region of the central nervous system. These infra-infundibular segmental nerves,
    No text description is available for this image
    No text description is available for this image
    No text description is available for this image