The sympathetic nervous system in disease / by W. Langdon Brown.

  • Walter Langdon-Brown
Date:
1923
Catalogue details

Licence: In copyright

Credit: The sympathetic nervous system in disease / by W. Langdon Brown. Source: Wellcome Collection.

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    greater sensiblitv, the pain is referred to the latter rather than to the former, where, however, the stimulus actually arose. To appreciate the clinical importance of this it is necessary to understand the distribution of cutaneous sensibility. The segmental arrangement of the primitive vertebrate still persists in the skin and muscles. Bolk calls the former dermatomes, the latter myotomes. Meta¬ merism is more obvious in the former. Both have a ring- shaped distribution in the neck and trunk, but in the limbs the metameric arrangement has become obscured in a way which is only intelligible when we recall their development. When we remember that the limbs arise as buds which have their axes at right angles to the trunk, we can see that the higher segments will be distributed along the pre-axial or primitive upper side of the limb, while the lower segments are placed along the post-axial side. So that the xOwest segments of all will be grouped around the coccyx and perineum, which represent the caudal region of the primitive vertebrate. The meta¬ merism of such efferent sympathetic nerves as the pilo¬ motor and vasomotor fibres to the skin corresponds with the dermatomes. These dermatomes overlap one another to a certain extent; but in the central part of each, sensibility is still preserved when all overlapping is abolished by section of the neighbouring posterior roots (Winkler & van Ryn- berk, Proc. Roy. Soc., 1901-2). The central portions of the dermatomes correspond with the zones of hyper¬ esthesia which Head found on the surface of the body in the presence of visceral disea.se. He explained them by saying that, when abnormal excitations from a diseased internal organ reach the cord by way of its afferent nerves, the excitability of the spinal segment becomes exag¬ gerated, so that when another cutaneous excitation of low intensity reaches the same segment it provokes pain, whereas under normal conditions it would only arouse a sensation of contact. And he also was able to demon- 2