The involuntary nervous system / by Walter Holbrook Gaskell.

  • W. H. Gaskell
Date:
1920
Catalogue details

Licence: In copyright

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

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    corresponding motor neurons of the somatic segmentation and supply in this region only dorso-ventral muscles. It is a great mistake to call this bundle of motor fibres the descending root of the trigeminal without adding the word motor ; the right dis¬ tinction between the two sets of trigeminal fibres called at present the “ descending ” and “ ascending ” roots is “ descending motor ” and “ descending sensory ” roots ; for the latter root behaves with respect to the somatic segmentation in exactly the same manner as the fasciculus solitarius, which is called the descending root of the vagus, with respect to the splanchnic segmentation. Similarly, in the mesosomatic region (Fig. i) the groups of motor cells, known as the facial nucleus and the nucleus ambiguus, represent the motor neurons of the splanchnic segmentation, and represent therefore the motor neurons of the muscles of the meso¬ somatic appendages ; they are quite separate from the nucleus of the abducens, which supplies motor fibres to the only remaining dorso-ventral muscles, a pair of which originally existed in each segment, and from the hypoglossal nucleus containing the motor cells of the longitudinal somatic muscles. These mesosomatic groups also extend down the cord ; the splanchnic group being represented by the nucleus accessorius or the lateral horn of the cervical region, which is formed from the lateral cell groups of the anterior horn ; the somatic group by the cells of the anterior horn, supplying motor fibres to the longitudinal trunk muscles. Thus the cells of the motor neurons of the voluntary system form two well-defined groups in accordance with the double segmentation of the striated musculature in the cranial region. On the sensory side (Fig. i) there are also two distinct sets of sensory fibres represented in the double segmentation, belonging respectively to the somatic and splanchnic segments. In the pro- somatic region the sensory neurons for both segmentations are found in the Gasserian ganglion ; but in the mesosomatic region the somatic sensory neurons belong mainly to the trigeminal and are also found in the Gasserian ganglion, while the splanchnic sensory neurons are found in the sensory ganglia on the facial, glossopharyngeal, and vagus nerves. So also there must be corresponding connector neurons for these two sets of segments, in order to carry out the primary or segmental reflexes, similar to those in the trunk region. These primary connector neurons are
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