Bell–Magendie law

History

The findings were described independently by two professors working in different medical paradigms: by Sir Charles Bell an anatomist and Francois Magendie – a pathophysiology and physiology professor . Their independent observations were 11 years apart. Another definitive experimental proof was given nine years after Magendie's experiments by Johannes Peter Müller during a vivisection of a frog in 1831.

Bell's discovery

In 1811 in a self-sponsored and published pamphlet Charles Bell referred to the motor functions of nerve fibers exiting the ventral roots of the spinal cord but did not mention the sensory functions of the dorsal roots. That was in part because his studies were dissectionist and not vivisectionist; pain is elicited and detected best in a conscious animal. A dead, or rendered unconscious, animal would not produce the desired effect when posterior horn fibers, responsible for sensation and transfer of noxious signals, are stimulated. Bell's nephew, John Shaw travelled in 1812 to Paris where he presented Bell's system to the French anatomists. Reportedly Shaw staged a demonstration on the facial nerves of a donkey without the intended effect.

Magendie's puppies experiment

Eleven years later, Magendie announced in the magazine Journal de physiologie expérimentale et de pathologie his discovery that the motor neuron fibers exit from the anterior root and the sensory neuron fibers from the dorsal root: "(trans)section of the dorsal root abolishes sensation, (trans)section of ventral roots abolishes motor activity, and (trans)section of both roots abolishes both sensation and motor activity."

Magendie gave the first complete description of the experimental proof of the Bell–Magendie law. His experiments were public, often conducted in the presence of medical students and curious citizens. That particular experiment was conducted by severing the anterior and posterior roots of spinal nerves in different combinations of several dogs in a litter of puppies. Stimulation of the posterior roots caused pain, and stimulation of the anterior – movement. The experiment was criticized for its cruelty by the Paris and London Humane societies. Detailed description of the experiment was published in the same magazine for physiology and pathology.

Müller's frog experiment

The third scientist, not credited in the name of the law, was the German physician and physiologist Johannes Peter Müller; he carried out neuroanatomical and physiological experiments on rabbits for quite some time and without success .

Then he decided to simplify his experiments, and thus analysis, by reducing the object of the study to a less complex nervous system – that of a frog. He was assisted by then student and later famous German physiologist and anatomist Theodor Schwann.

Because the frog spinal cord is relatively simple and easy to remove, and the relationships between the nerve roots are more apparent, Müller could simplify his design, which also resulted in better reproducibility of the experiment. His experiment involved innervations of the hind legs of the frog. One procedure involved first severing the posterior roots of the spinal nerve leading to the leg, with the result that the leg became insensible but not paralyzed. The second part of his experiment involved severing the anterior roots, so that the limb became paralyzed but not insensible. Müller's frog experiment became a physiology professor's favorite – it was an easily reproducible experiment, and has been used widely in teaching neurophysiology.