Hauke Werner, along with a working group from the Max Planck Institute for Experimental Medicine in Göttingen are researching the link between myelin and axon function. Whether this interaction limits the diameter of the axons, and to what extent, has been unclear until now. The myelin-forming cells in the peripheral nervous system, known as Schwann cells, are wound tightly around the axons. Insulating the axons also enables rapid signal transmission over long ranges, such as in larger animals like the giraffe. More axons can fit into one nerve path, enabling a greater precision in signal conduction and the development of complex cognitive functions. There are many reasons why this has an advantage for vertebrates: smaller axons not only use less energy, they also need less space. Myelin enables a fast stimulus conduction even in axons with a small diameter. Myelin formed, surrounding and electrically insulating the nerve fibres with a multi-layered, fat-rich sheath. Invertebrates such as squid have some very large axons which achieve high transmissions speeds.īy contrast, the speed of signal transmission in the vertebrate nervous system has increased by a different evolutionary process. Thicker axons offer less resistance to the electrical signal, enabling swifter transmission. One of the factors influencing the speed with which this signal transmission occurs is the diameter of the axons. The nerve cells conduct electrical impulses along their extensions – the axons – culminating in a contraction of the muscles. In order to flee from a predator or to hunt successfully, animals have to be able to react swiftly to external stimuli. Since neurological diseases such as Charcot-Marie-Tooth disease exhibit reduced axon diameter, CMTM6 could present a possible target for therapies. They subsequently observed that the mice not only developed thicker axons, but also reacted significantly more quickly to sensory stimuli compared to their peers. Researchers at the Max Planck Institute for Experimental Medicine in Göttingen have succeeded in genetically switching off the CMTM6 protein in myelin-producing cells in mice. Until now, however, no-one has identified a molecule that limits axon thickness. This insulating layer enables rapid stimulus conduction with a small axon diameter. Whereas some invertebrates have developed very thick axons to increase the neural transmission speed, in vertebrate nervous systems a myelin sheath has formed around the axon. In order for organisms to react swiftly to stimuli in their environment, they need rapid and precise transmission of nerve impulses along neural extensions known as axons.

Speed of neurons in the brain