The involuntary nervous system / by Walter Holbrook Gaskell.

  • Gaskell, Walter Holbrook, 1847-1914.
Date:
1920
Catalogue details

Licence: In copyright

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

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    it is no longer suitable. So far as the term system can be used at all, we are dealing only with motor cells and motor nerves to a special set of tissues, and with the connexions of such motor neurons with the central nervous system. There is one charac¬ teristic common to these special tissues, they are not directly under the command of the will. The motor nerve cells in ques¬ tion invariably send motor nerve fibres to involuntary muscles or glands, just as the motor nerve cells in the central nervous system send motor nerve fibres to voluntary muscles. The natural term then to use, if we wish to group together these vagrant motor cells and their connexions into one system, is to speak of it as the involuntary nervous system in contradistinction to the voluntary nervous system ; meaning thereby a system of motor nerve cells to involuntary structures, which have left the central nervous system and have migrated out to a greater or lesser distance. Now the vertebrate body is undoubtedly segmented ; that segmentation is shown on the motor side by the segmentation of the body muscles in the trunk region to form the myotomes, and by their innervation by the motor nerves, which pass from the anterior horn cells into each spinal nerve; again on the sensory side it is shown by the presence of the posterior root ganglion in each segment and the distribution of its sensory nerves to a de¬ finite segmental skin area. Each spinal nerve then is a segmental nerve as far as concerns the central and peripheral distribution of its motor and sensory components. We may then inquire how far such an arrangement also obtains in the case of its sym¬ pathetic components. The motor fibres which supply the muscles of the involuntary system arise from the vagrant ganglion cells of that system, and in the case of the so-called sympathetic part of that system, form the grey rami communi- cantes. These grey rami from each of the ganglia of the lateral or main chain supply the corresponding spinal nerve, and, as Langley has shown in the case of the pilo-motor muscles, reach their destination by way of the cutaneous branches of that nerve ; they thus afford evidence that these segmentally arranged motor neurons are closely associated in the adult with the segmental cutaneous sensory neurons, which must be the case if they have separated out from a conjoined mass of sensory and motor neurons, as Onodi has shown. Here then in the lateral ganglia of the sympathetic chain we find the true segmental motor nerve