Myelin is a material that forms a layer around the axon of a neuron. Schwann cells wrap around axons and produce these myelin sheaths, which are spaced between gaps called the nodes of Ranvier. The main purpose of myelin is to allow nerve impulses to move very quickly along the axon, but the relationship between nerve conduction velocity and the distance between myelin sheaths was unclear. Recently, Wu and colleagues measured conduction velocity in mice with Schwann cells carrying a mutation that prevented elongation of Schwann cells. In these cells with short Schwann cells, and in turn short distances between nodes of Ranvier, conduction velocity dropped and motor function of the mice was impaired. As these mice developed and the internodal distance increased, nerve conduction velocity and motor function recovered. Wu and colleagues suggest that the high conduction speed reached by increasing internodal distance reaches a “flat maximum.” Above, cross-sections of nerves in mice at 3 (top) or 24 (bottom) weeks old show some differences in myelin between normal mice (left column) and mice with a Schwann cell elongation mutation (right column). 24-week old mutants show some myelin folds and some structures indicative of demyelination and remyelination (arrowheads, bottom right).
Wu, L., Williams, A., Delaney, A., Sherman, D., & Brophy, P. (2012). Increasing Internodal Distance in Myelinated Nerves Accelerates Nerve Conduction to a Flat Maximum Current Biology, 22 (20), 1957-1961 DOI: 10.1016/j.cub.2012.08.025Copyright ©2012 Elsevier Ltd. All rights reserved.
No comments:
Post a Comment