39

The History of Bioelectromagnetism

Ichiji Tasaki (1910–2009) was the pupil of Gen-ichi Kato, Japanese-born American biophysicist. He

was frst working in Japan and later worked as a visiting scientist at research institutions in Switzerland

and England. Ten he went to the United States and joined the National Institute of Health (NIH) in

1953. During his scientifc carrier in 1939, he studied anesthetics on isolated nerve fbers, discovered the

insulating function of myelin sheaths (the nodes of Ranvier), and showed that action potential can jump

actually over the anesthetized region between nodes of Ranvier; later he called this process saltatory

conduction (Tasaki, 1939 a, b).

Historically, the idea of saltatory conduction of the action potential in myelinated axons seems to

have originated in 1925 with Ralph Stayner Lillie (1875–1952), professor of General Physiology at the

University of Chicago, USA (Lillie, 1925). He modeled the nodes by enclosing iron wire in a glass insu­

lant tube containing dilute (70%) nitric acid with periodic breaks. He showed that electric conduction

occurred faster in saltatory fashion.

Gen-ichi Kato and his pupil, Tasaki, introduced the technique with myelinated axons of frog nerves.

Huxley and Robert Stämpfi (1914–2002), professors at the University of Berne, Switzerland, developed

the technique to measure the resistance and capacitance of myelin. By drawing single myelinated nerve

fbers isolated from the sciatic nerve of frogs through a glass capillary and measuring the current fow­

ing around the outside of the fber during the passage of an action potential, Huxley and Stämpfi proved

exactly the existence of saltatory conduction of the action potential from node to node in isolated frog

nerves (Huxley and Stämpfi, 1949). Teir work confrmed Tasaki’s fndings. Te concept of the saltatory

conduction is featured in the textbooks of physiology.

Conduction velocity of action potential in myelinated fber depends on distance of neighboring

Ranvier nodes, as duration of action potential is about 1 m/s in any nerve fbers. Distance of neighbor­

ing Ranvier nodes depends on diameter of nerve fbers; distance is longer in thicker fbers. Tere are

myelinated and unmyelinated fbers with diferent diameters in mammalian nerves. In unmyelinated

fber impulse conduction is continuous, and therefore conduction velocity is much slower than myelin­

ated fbers. Masamichi Kato, professor at Hokkaido University, measured conduction velocity of human

ulnar nerve of the arm with results of about 67 m/s (Kato, 1960).

Te properties of ion channels and the propagation of nerve signals were obtained from the study of

the current clamp and the voltage clamp in electrophysiology. In 1939, using extracellular electrodes,

Kenneth Steward Cole and Howard James Curtis, both at Columbia University, performed measure­

ment by alternating current impedance over a wide frequency range on the giant axon of a stellar nerves

of Atlantic squid, Loligo pealei which is about 0.5 mm in diameter and its segment is 3–8 cm long (Cole

and Curtis, 1939). Tey demonstrated the rapid fall in membrane resistance during the development of

the action potential. Soon afer, the intracellular electrode was developed by Cole, Curtis, Hodgkin, and

Huxley, by inserting the electrodes directly into the squid axon, direct recordings of action potential

were performed.

In 1949, the voltage-clamp technique was designed by Cole and employed by Hodgkin and Huxley

to produce the ionic theory of membrane excitation. Tey demonstrated that membrane excitability is

determined by passive ion fux according to their electrochemical gradient (Verkhratsky et al., 2006).

During the 1950s, Hodgkin and Huxley began to understand the electrical nature, action potential in

the axon of the giant squid by using their developed intracellular electrode. Tis electrode could be

inserted into the squid axon. Tey recorded the frst time directly action potential. From such experi­

ments, they discovered the ionic mechanism of excitation and inhibition in nerve cell membranes and

developed the mathematical model of the activation process. In 1952, Hodgkin and Huxley published a

series of fve papers in the Journal of Physiology (Hodgkin and Huxley, 1952a–d; Hodgkin et al., 1952).

Te characterizations of the changes during action potential were described in the frst four papers

and in the last paper the mathematical model was presented. Te model explains the ionic mechanism

underlying the initiation and propagation of action potential in the squid’s giant axon. Sir John Carew

Eccles, Australian physiologist, investigated the synaptic transmission of ions, the behavior of the cell

membrane. Tese three specialists won the Nobel Prize in Physiology or Medicine in 1963 for their