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The History of Bioelectromagnetism

In Berlin, Müller proposed the theory of specifc nerve energies. His proposed doctrine was that a

particular sensation depends on the nature of the sensory receptors that had been stimulated, and that it

was the function of a receptor to convert the energy of the stimulus into impulses (action currents) in the

nerve fber (McComas, 2011). He also developed the concept of electric signal propagation through the

nerve. Müller’s pupil and assistant, Emil du Bois-Reymond (1818–1896), 8 years younger than Matteucci,

a Swiss-German physiologist, professor at the University of Berlin, started the investigation of animal

electricity using electric fsh, and moved to the study of current impulse arising from nerves and muscles

of frog legs using of galvanometer in 1842. In order to do, he invented the galvanometer with 4,650 wind­

ings of a wire (1 km long and 0.17 mm in diameter) and developed a more sensitive galvanometer with

over 24,000 windings and 5 km long wire (Rowbottom and Susskind, 1894). du Bois-Reymond was the

frst to measure the potential diference accompanying nerve and muscle excitation. He repeated these

observations and discovered the action potential. Tis galvanometer was used for several decades in the

research feld of neurophysiology. Hermann Ludwig Ferdinand von Helmholtz (1821–1894), a German

physicist and physiologist, professor at the University of Berlin, was the frst to measure during his work

in Heidelberg, the conduction velocity of a nerve cell axon in 1850s. He showed the propagation of action

potential, by measuring the delay time between an electric stimulation of the nerve and muscle contrac­

tion of frogs. Te values of action potential propagation were experimentally in the range of 25–40 m/s.

Te phenomenon of electric current fowing through a nerve cell with a certain resistance and capac­

ity is called electrotonus, which was frst studied around the end of the nineteenth century. In electro-

physiology, tonus is the slight contraction of a muscle. Electrotonus refers to the altered electrical state

inside a neuron and between cardiac muscle cells or smooth muscle cells from passive electric current.

Te research of electrotonus began mainly in Germany in the middle of the nineteenth century. At this

time, the long distance telegraphic cable laying work began between the continents. In 1855, William

Tomson (later, Lord Kelvin, 1824–1907), a British physicist, professor in the University of Glasgow,

proposed a theoretical model called the cable theory (Tomson, 1854–1855). Tis theory provided the

understanding of electrical propagation of the Atlantic submarine (undersea) telegraphic cable. Te

proposed theory takes only the capacitance and resistance of a cable into the calculation and it was later

corrected by Heaviside. Oliver Heaviside (1850–1925), a British physicist and electrical engineer, applied

the cable theory to analyze the submarine (undersea) telegraphic cable in 1876. From his cable the­

ory, the electrical characteristics of the excitation of nerves and muscle cells could be analyzed. Oliver

Heaviside used for the frst time the terms, impedance (1886), conductance (1885), permeability (1885),

admittance (1887), and permittance (susceptance). Te terms are used not only in electrical engineering,

but also in neurophysiology. Te properties of nerve fbers can be derived from the solution of the cable

theory because the electric properties of the nerve fbers are similar to that of the submarine (undersea)

telegraphic cable. If we consider a simple nerve fber, we can use the submarine undersea cable theory as

a model to represent the nerve fber in form of an electric circuit. Te resistance of the protoplasm, the

resistance of the cell membrane, and the capacity of the cell membrane can be used to describe nerve

fbers by the cable theory. Te cable theory can be applicable to the characterization of electric conduc­

tion along a nerve fber. Excitation of nerve and muscle cells can also be analyzed using the cable theory.

Until the early twentieth century, the advantage of applying the cable theory to nerve fber conduc­

tion was not recognized. In 1945, Kenneth Stewart Cole (1900–1984), an American biophysicist, Alan

Lloyd Hodgkin (1914–1998), a British biophysicist, and William Albert Hugh Rushton (1901–1980) devel­

oped the mathematical theory of nerve fber conduction based on the cable theory. Te measurement

technique for the electric activity of a neuron was improved in the 1950s. In order to understand the

electric properties of neuron, the cable theory may also be suitable.

Julius Bernstein (1839–1917) studied medicine at the University of Berlin as a pupil of Emil du Bois-

Reymond and trained for a time under Helmholtz as an assistant to record the action potential. Te

available instruments for the measurement and recording of the action potential were galvanometers.

Te galvanometer was still slow to respond, and its response time was in the order of seconds. At the time

when Julius Bernstein was at the University of Halle, Germany, he developed more sensitive equipment