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 [HT.1 - transfer of copyright] dated 12:00 13th January 2010

 

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).  

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.

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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.