The Nobel Prize in Physiology or Medicine 1944
Joseph Erlanger, Herbert S. Gasser
In regard to Erlanger's and Gasser's works, Professor R. Granit, Head of the Department of Neurophysiology of the Nobel Institute of the Royal Caroline Institute, made the following statement*.
Three great electrophysiological
discoveries can be regarded as milestones in the development of
our knowledge of nerve physiology. In the middle of the last
century, long before Alfred Nobel
had bequeathed this great fund to the world, Du Bois-Reymond
showed that the nerve impulse was an electrical wave of
negativity transmitted along the nerve. Helmholtz
made the first measurements of its average speed of propagation
in a nerve stem. The second great discovery, rewarded with a
share in the Nobel Prize for
1932, was Adrian's
observation that sense organs and nerve cells discharge whole
series of such impulses. In each individual fibre the nerve
impulse is of constant size but the stronger the stimulus, the
greater the frequency of the impulses discharged along the nerve.
The nerve cells, as it were, communicate with each other by a
kind of machine-gun fire. This description of the mechanism is
inadequate from the standpoint of physics but otherwise
illuminating. And, indeed, if the impulses are led to a
loudspeaker over an amplifier it does sound like machine-gun
fire. The discoveries of Erlanger and Gasser constitute a third
step forwards.
In 1907 the Swedish physiologist Gustaf Göthlin made the
assumption that conduction velocity in thick nerve fibres is
greater than in thin ones. The basis for this view was W.
Thompson's formula for electrical-cable conduction. This
assumption gave a physiological interpretation of the well-known
fact that the individual fibres of a nerve stem vary in cross
section. Some fibres are less than 0.001 mm in diameter, others
just above 0.020 mm. Lapicque and his colleagues, from 1913
onwards, published some papers in which indirect evidence in
support of this view was advanced. In a series of remarkable
papers - remarkable in respect of both technique and wealth of
new information unearthed - Erlanger and Gasser proved this
hypothesis to have been correct. As so often happens in
experimental sciences, the additional steps necessary for full
clarity as well as the development of an elegant new technique,
heralded an experimental expansion of great width and
significance. The seemingly simple cables turned out to have been
endowed with a high degree of differentiation. Since nerve fibres
are to be regarded as extensions of nerve cells these results are
indeed of extreme importance for the physiology of the higher
centres such as the brain and the spinal cord. This fact should
be given especial consideration in appraising the significance of
the work of Erlanger and Gasser.
Erlanger and Gasser showed that the nerve fibres, according to
their conduction velocities, could be divided into three main
groups of which the first, group A, could be further subdivided.
The thickest mammalian fibres, the A-fibres, conduct impulses as
fast as from 5 to 100 metre per second, the thinnest, the
C-fibres, have conduction velocities below 2 metre per second.
Between these two groups there are the B-fibres with conduction
velocities from 3 to 14 metre per second. A large number of other
properties of the nerve fibres vary with the speed of conduction,
for instance, the duration of the impulse, its rate of rise, its
size, the duration of the inexcitable or refractory period
following each impulse, the threshold of excitation, the
sensitivity of the discharge to pressure on the nerve and to
asphyxia, in short, an array of properties connected with impulse
conduction all of which need not vary in an exactly parallel
manner. Erlanger and Gasser also showed how this highly
differentiated system with its three main types of fibre was
distributed over the in- and outgoing fibres of the spinal cord,
the so-called sensory and motor roots. The perception of pain is
largely mediated by very thin, slowly conducting fibres, muscle
sense and touch by rapidly conducting fibres. The muscles of the
body are also thrown into movement by fast fibres.
In the brain and the spinal cord the time ratios of the impulses
are of primary importance for the cooperation of the nerve cells.
A difference of 0.001-0.005 seconds in the time of arrival of
impulses means that a given path may be found opened or closed
for their passage onwards. Problems of this kind belong to the
present-day programme of experimentation in these fields.
The admirable technique of Erlanger and Gasser soon showed them a
road to new discoveries, chiefly concerned with the changes of
excitability that occur at a nerve cross section at which
impulses arrive. The arrival of one or several impulses to such a
region was found to be followed by slow changes of excitability
which were associated with slow changes of electrical potential,
studied in detail by Gasser. These changes of excitability
enhance or depress succeeding impulses. Such
«after-potentials» had been seen before, but Gasser and
his collaborators demonstrated their independent character and
showed that they behaved in a different manner in the three main
types of fibre. The concept of a high degree of differentiation
of the nerve fibres for their different tasks was thus again
supported by a new group of facts. These are of particular
importance for the physiology of the central nervous system. A
prominent feature of this region is interaction between
excitation and inhibition in close association with slow
potential changes. Erlanger and his collaborators devoted
themselves to an analysis of the changes of excitability in a
nerve influenced by a constant electrical current. One of their
most important discoveries was the demonstration that sensory
nerves in many respects differed from motor nerves. The sensory
nerves had, for instance, lower thresholds of excitation and they
put up less resistance to impulse generation (less
«accommodation») than motor nerves. This fresh
contribution to the differentiation among the nerve fibres has
far-reaching consequences.
When today Erlanger and Gasser receive the 1944 Nobel Prize for
their discoveries concerning the highly differentiated properties
of single nerve fibres, it might be pointed out that their
achievement was not born, fixed and armoured, in the manner of
the birth of Pallas Athene. But no sooner had their first result
given them the key word than discovery followed hard upon
discovery until their colleagues everywhere in the world came to
realize that a great new synthesis had been born to nerve
physiology. This synthesis is based on new facts, well-hardened
by a masterly technique cementing them into a groundwork on which
will be erected whatever structure the future has in store for
the physiology of the central and peripheral nervous system.
*Broadcast lecture delivered on the 10th December, 1944.
From Les Prix Nobel en 1944, Editor Arne Holmberg, [Nobel Foundation], Stockholm, 1945
Copyright © The Nobel Foundation 1944
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