When it comes to sending electrical nerve signals, some messages are more urgent than others. Our muscles need to be activated quickly when we are attacked, for instance, while our receptors for chronic pain do not require such a rapid response. To meet these various delivery requirements, nerve fibres differ considerably in the way they transmit and fire signals. Understanding these variations is an ongoing task, but for recording these differences and showing how they relate to nerve design, Joseph Erlanger and Herbert Gasser were awarded the 1944 Nobel Prize in Physiology or Medicine.
Erlanger and his student Gasser were interested in developing tools that could measure impulses fired through nerve cells, and they turned to the cathode-ray oscilloscope – an instrument that allows electrical currents to be visualized as a moving two-dimensional graph on a phosphorescent screen. After its invention by Ferdinand Braun, the oscilloscope soon became the most effective tool for detecting rapid changes in electrical voltage, but still it was not sensitive enough to measure the weak and rapid electrical impulses that are fired along nerve cells. Erlanger and Gasser solved this problem by constructing an amplification device which magnified the minute impulses in a single nerve fibre millions of times, so that they became visible as distinctive waves on the screen.
Using their apparatus, Erlanger and Gasser found that stimulating isolated nerves with identical single shocks created a variety of waves on the screen. Deconstructing this complex pattern revealed that nerve fibres conduct impulses at different rates depending on their thickness. On this basis, fibres could be classified into three distinct types, and Erlanger and Glasser also showed that each type requires a stimulus of different intensity to create an impulse. From their observations, Erlanger and Glasser formulated a theory proposing that different fibres transmit different kinds of impulses, where touch travels along thicker, rapidly conducting fibres, while pain is mostly perceived by very thin, slowly conducting fibres. In other words, they showed how the functionality of our central nervous system relies on the precise timing of its tasks.
By Joachim Pietzsch, for Nobelprize.org
This Speed read is an element of the multimedia production “Nerve Signaling”. “Nerve Signaling” is a part of the AstraZeneca Nobel Medicine Initiative.