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Tuesday, October 2, 2012

Charles Sherrington

 

The English physiologist Sir Charles Scott Sherrington (1857-1952) described the fundamental mechanisms of the working of the mammalian nervous system. He formulated the principle of the reciprocal innervation of effectors and discovered the functional significance of muscle receptors.
Charles Scott Sherrington was born on Nov. 27, 1857, in Islington. He began his medical studies at the Royal College of England and ended them in 1879 at St. Thomas Hospital in London as a fellow of the Royal College of Surgeons. Then he went to Cambridge, where he soon became a fellow of Caius College.
Neurophysiology soon attracted Sherrington, and his first two publications, which he authored in collaboration with J. W. Langley, were devoted to the study of secondary degenerations of the spinal cord of a dog which had undergone an experimental excision of the cerebral cortex. These papers revealed Sherrington's mastery over histological techniques which were such an important asset in his later research.
In 1892 Sherrington married Ethel Wright. In 1895, after a short period devoted to travel during which he was attracted by anatomopathology and bacteriology, he was appointed to the chair of physiology at Liverpool, which allowed him to develop his experimental activity in a well-equipped laboratory.
At the end of the 19th century neurophysiology had just accomplished a decisive step. The spinal cord was no longer a bundle of conducting fibers with no other function than connecting the brain with the somatic receptors and the muscles, for the demonstration had been made once and for all of its reflexive function. It was also demonstrated that the column of gray matter, interposed between the dorsal and ventral roots, played an important role in nerve cord performance and that this gray matter was composed of myriads of nerve cells linked to one another without protoplasmic confluence. The notion of a relation between the irreciprocity of central nervous conduction and the existence of this structural and trophic discontinuity of the central neuronal nets had become apparent. On the other hand, the study of the neural reactions in invertebrates had revealed the interplay of elementary processes very similar to those whose participation in the functioning of the neuraxis of vertebrates was only beginning to appear.
No coherent doctrine had emerged from these fragmentary observations until 1906, when Sherrington's Integrative Action of the Nervous System was published. This book, which contained the Silliman Lectures he delivered at Yale University in 1904, was a milestone in its field.
Integrative Action
The chain of processes, making the spinal cord isolated from the brain a mechanism of high precision and a perfect functional unity, was set forth in a series of logically ordered chapters. Locomotion in mammals was shown to be the result of the orderly cooperation of a group of reflexes admirably adapted to their ends, successively calling each other in a strict temporal and causal seriation through the action of dynamic factors. The study of certain rhythmical reflexes led to the fundamental distinction of the respective functional roles of interneurons and motor neurons. The organization of central autochthonal rhythms was the prerogative of the former, whereas the emission of efferent impulses, both reflex and voluntary ones, was the function of the latter, constituting a "final commonpath."
Sherrington described another more complex neural machinery: the decerebrated preparation with its peculiar characteristic of the permanent contraction of muscles which antagonize gravitation. He definitively characterized as genuine reflexes such brief contractile responses as are aroused by tendinous percussion acting through the sudden elongation of the neuromuscular spindles. The cerebral cortex, which is the warden of associative memory, informed by the telereceptors which greatly enlarge the perceptual space, crowns the neural construction of mammals. It confers unto the creature the power of adaptation to the incessant variations of the environment within which it must defend its ephemeral integrity to ensure the survival of the species. Such was, in its majestic order, this henceforth classical monument of neurophysiology.
Other Discoveries
World War I, in which Sherrington served for the National Defence, interrupted his physiological research at Liverpool. Then came his work at Oxford. This stage of his career permitted him, assisted by enthusiastic young researchers, to add to the edifice of his work the precision and the enriching which electronic progress now made possible. He introduced the notions of central excitatory and central inhibitory states, neutralizing each other algebraically and interpreted as the manifestations of opposite changes in the nervous cells' membrane polarization. The nice intracellular oscillographic recordings, realized by one of his assistants, which Sherrington did not live to see, confirmed the soundness of his foresight through the materialization of postsynaptic potentials of excitation and inhibition. From the same period dates the analysis--a model of quantitative precision--with E. G. T. Liddell, of the myotatic reflex, base of the muscular tonus. Sherrington also discovered the functional role of the thin motor fibers which innervate the neuromuscular spindles.
Sherrington's scientific accomplishment was astounding by its wideness and diversity. For example, he collaborated on a set of excellent studies on primate cerebral cortex between 1901 and 1917. These studies confirmed the explanatory value of the dynamic factors of the central nervous apparatus deduced from the analysis of the spinal mechanisms.
In 1932 Sherrington shared the Nobel Prize in physiology or medicine with E. D. (later, Lord) Adrian. In honoring their work the Nobel Prize Committee acknowledged that biological research inspired solely by philosophical curiosity and free from any concern with immediate medical application would some day help those whose work was aimed directly toward the improvement of the human lot.
In Man on His Nature (1942), which is Sherrington's philosophical testament, and in the preface which he wrote in 1947 for the sixth edition of Integrative Action, he explained what he meant by the word "integration." He underlined the distinction necessary between the purely motor integration of the decerebrate animal and the complete conscious one of the sensing being. An excerpt from the preface sheds more light on his position concerning the mind-brain problem and explains why Ivan Pavlov once harshly accused him of dualism and of animism. With regard to psychophysiological parallelism, Sherrington mentions the two complementary syntheses which occur simultaneously in the intact nervous system: the physicochemical, which makes an aggregate of interdependent organs into a goal-seeking machine, and the psychological, which integrates an array of perceptual processes into an individual conscience, with its emotions, its aspirations, its volitions, and its memory. He wonders whether these two parallel integrations are commensurable. His position was definitely not the expression of a religious belief. It simply translated the anxiety of the philosopher and the poet of Man on His Nature faced with the mystery of human destiny

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