Volume 4

Studies in neurology / by Henry Head ; in conjunction with W.H.R. Rivers [and others].

  • Henry Head
Date:
1920
Catalogue details

Licence: Public Domain Mark

Credit: Studies in neurology / by Henry Head ; in conjunction with W.H.R. Rivers [and others]. Source: Wellcome Collection.

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    from intramedullary disease with the maximum supply of posterior roots led to nothing but confusion. No clinician seems to have recognised that the complete cutaneous dis¬ tribution of a nerve, of a posterior root or of a segment of the spinal cord, could only be discovered by observing how much of the skin was sensitive, when that afferent path alone remained intact. If we wish to know how much of the palm is supplied by the median nerve, we cannot do so by observ¬ ing the extent of the loss of sensation caused by its division. A case must be selected where the ulnar, the radial and the external cutaneous nerves have been divided; then, any part of the hand which remains sensitive must receive its innervation from the median. ’ This is the method of residual sensibility invented by Sherrington, and so ably employed by him to discover the maximum afferent distribution of each posterior root. If we wish to determine the exact level of the affected intramedullary segment, we are compelled to adopt an indirect method. For lesions within the spinal cord, such as those produced by fracture of the spine or rapidly spreading growths, lead to widespread destruction. However well defined may have been the disturbance of sensation, some disease will be found corre¬ sponding to parts beyond its limits. Moreover, the opportunities are too limited for correlating these areas of residual sensibility with the extent of intramedullary disease. Head [44] showed that there is a close correspondence between the dis¬ tribution of the tenderness caused by irritation of the segments within the spinal cord, concerned with the reception of painful impulses, and the areas marked out on the skin by the eruption of herpes zoster. Now, herpes zoster is due, in most cases, to acute inflammation of a posterior root ganglion, whereas the tender areas in visceral disease are due to the irritation of intramedullary segments. But, though all the cells and the fibres peculiar to them must be affected by the profound inflammation of the ganglion, one system only, as far as we know, can produce an antidromal effect upon the skin. These are the fibres shown by Bayliss [4] to have their cells of origin in the ganglion of the posterior root. Bayliss, in conjunction with one of us, has been able to show, that these antidromal fibres are capable of excitation in the divided nerve of a cat, five weeks after it has been reunited to the central nervous system. In the time and manner of their regeneration, these fibres closely resemble those of the protopathic system. Thus, it is probable that this power of producing acute changes in the skin of the periphery is a function of fibres, which run in the protopathic system. On this hypothesis, the eruption of herpes zoster would correspond to the distribution of the fibres and cells of the protopathic system in the ganglion of the posterior root. Now Head and Sherren showed, that division of several posterior roots