Lecturer's Précis - Bell (1811) / Magendie (1822)
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First published online 10:40 GMT 11th March 2002,
Copyright Derek J. Smith (Chartered Engineer). This
version [2.0 - copyright] 09:00 BST 8th July 2018
Sir Charles Bell and François Magendie's Anatomically Grounded Sensorimotor Hierarchy
The Scottish physician Sir Charles Bell (1774- 1842) published New Anatomy of the Brain in 1811. In it he analysed the organisation of the spinal cord and proposed a fundamental distinction between sensory and motor functions. The motor tracts, he claimed, ran ventrally (ie. on the anterior, or forward, aspect of the spinal cord in a two-footed animal). The French physiologist Francois Magendie (1783-1855) confirmed Bell's analysis 1822 by adding that the sensory tracts ran dorsally (ie. on the posterior, or backward, aspect of the spinal cord in a two-footed animal). This tract-separation principle has since become known as the Bell-Magendie Law. Magendie's work is well illustrated by the following description of an experiment upon a puppy:
"I
was able with the help of a very sharp scalpel to expose the posterior half of
the spinal marrow. I was able to cut the posterior roots of the lumbar and
sacral pairs on one side. [] I reunited the wound by a suture, and then
observed the animal. I at first thought the member was paralysed because it was
insensible to the strongest prickings and pressures.
But soon, to my great surprise, I saw it move. I began to think it probable
that the posterior roots of the spinal nerves might have different functions
from the anterior roots. It naturally occurred to the mind to cut the anterior
roots, leaving the posterior untouched. As in the preceding experiment, I made
the section on one side only, in order to have a point of comparison. The
member was completely immovable and flaccid, at the same time preserving its
sensitivity. Finally, that nothing might be neglected, I cut the anterior and
posterior roots at the same time. There ensued absolute loss both of
sensibility and of motion." (Magendie,
1822).
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Bell (1811); Magendie (1822): Sensory fibres from each peripheral nerve enter the spinal cord via the sensory roots (blue cluster, lower right), and then ascend via the dorsal columns of the spinal cord to the brainstem. Motor fibres leave the spinal cord via the motor roots (red cluster, lower left), having descended via the anterior columns of the spinal cord. Captions above the level of the brainstem show the more complete understanding of brain location established by research later in the nineteenth century. If this diagram fails to load
automatically, it may be accessed separately at |
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Copyright © 2002, Derek J. Smith. |
References
Bell, C. (1811). Idea of a New Anatomy of the Brain. London.
Magendie, F.J. (1822). Expériences
sur les fonctions des racines des nerfs. Journal de Physiologie
Expérimentale et Pathologique, 4.