Julius Bernstein (December 18, 1839 – February 6, 1917)

Julius Bernstein 

(December 18, 1839 – February 6, 1917)  

German physiologist who was born in Berlin. He studied medicine at the University of Breslau under Rudolf Heidenhain, and at the University of Berlin under Emil Du Bois-Reymond. He received his medical degree at Berlin in 1862, and began his career at the Physiological Institute of the University of Heidelberg as an assistant to Hermann von Helmholtz. In 1872 he succeeded Friedrich Goltz as professor of physiology at the University of Halle. Bernstein remained in Halle for the remainder of his career.

Bernstein's work was concentrated in the fields of neurobiology and biophysics. He is remembered for his explanation regarding the origin of the "resting potential" and "action potential" of nerves and muscles. In 1902 he developed the "membrane theory" of electrical potential in biological cells and tissues, which provided the first practical physico-chemical explanation of bioelectric events. This hypothesis is considered the first actual quantitative theory in electrophysiology.

Bernstein (1902, 1912) correctly proposed that excitable cells are surrounded by a membrane selectively permeable to K+ ions at rest and that during excitation the membrane permeability to other ions increases. His "membrane hypothesis" explained the resting potential of nerve and muscle as a diffusion potential set up by the tendency of positively charged ions to diffuse from their high concentration in cytoplasm to their low concentration in the extracellular solution while other ions are held back. During excitation, the internal negativity would be lost transiently as other ions are allowed to diffuse across the membrane, effectively short-circuiting the K+ diffusion potential. In the English-language literature, the words "membrane breakdown" were used to describe Bernstein's view of excitation. (From Ion Channels of Excitable Membranes, Third Edition, by Bertil Hille).

His pioneering research laid the groundwork for experimentation on the conduction of the nerve impulse, and the transmission of information in the nervous system. Bernstein also invented a "differential rheotome", a device used to measure the velocity of bio-electric impulses.

http://en.wikipedia.org/wiki/Julius_Bernstein