Renato M.E. Sabbatini, PhD
In the second half of the 19th century, the neurosciences continued to advance at a fast pace, fueled by the basic tenets of biophysics, the new interdisciplinary union welded together by the reductionists, as well as by the neuroanatomists.
In 1869, Otto Friedrich Karl Deiters proposed that the neuron cells had two different kinds of branching processes: dendrites and axons (these terms, however, were introduced later on: "dendrite" in 1889, by William His; "neuron" in 1891, by Wilhelm von Waldeyer and "axon" in 1896, by Rudolph Albert von Kolliker. Advances in this area culminated with the so-called Neuron Doctrine, established as a result of the remarkable work done by Spanish anatomist Santiago Ramon y Cajal (1852-1934) and Italian anatomist Camillo Golgi (1843-1926), who received the 1906 Nobel Award in Medicine and Physiology.
Camilo S. Golgi
|Santiago Ramon y Cajal|
In electrophysiology, among others, the German physiologist Julius Bernstein (1839-1917) made a great number of contributions to the understanding of how the nerve membranes were polarized and depolarized during the action potential (a term coined by him). He proposed around 1870 the modern theory that the inactive nerve or muscle fiber is normally electrically polarized, with the external surface positive in relation to the internal one, and that the action potential is a self-propagated depolarization of the membrane.
In the late 19th century great advances were made in the measurement of the time course and precise electrical variations during bioelectric potentials. The American physiologist H. P. Bowditch (1840-1911) determined that the muscle action potential was an all-or-nothing phenomenon. Francis Gotch (1853-1913) did the same for the nerve action potential.
Herbert S. Gasser
Edgard D. Adrian
However, it was the invention of the cathode ray oscilloscope, used brilliantly by American physiologists and 1944 Nobel prize winners, Herbert Spencer Gasser (1888-1963) and Joseph Erlanger (1874-1965) that the doors were open for technically sophisticated investigations of the electrophysiology of nerves and muscles, beginning with their landmark paper in 1922, titled "A study of the action currents of nerve with a cathode ray oscillograph" (Journal of Physiology, London, 62: 496). With these techniques, the precise time course of the action potential, the refractoriness period, the local graded responses to stimulation (electrotonic potentials) and the ionic nature of all-or-nothing responses were demonstrated by them and many other scientists, such as Edgard D. Adrian (1889-1977), also a Nobelist (1932). Erlanger and Gasser also showed that the nerve fibres can be subdivided into three groups, according to their conduction velocities.
Nerve ConductionTools of the Trade
A descoberta da Bioeletricidade
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Center for Biomedical Informatics