NEUROGLIA

For the past 160 or so years the cells of the nervous system have been divided into two main categories: neurons and glia (Kettenmann and Verkhratsky, 2008). Prior to this, ever since the first image of a neuron was published in 1836 by Gabriel Valentin, the nerve cell had been in a class of its own (Lopez-Munoz et al., 2006). Some 20 years later in 1856 the term neuroglia was introduced by the German physician Rudolph Virchow. Virchow, also known as the “Pope of pathology” (Kettenmann and Ransom, 2005; Magner, 2002), described a “connective substance … in which nervous system elements are embedded” and referred to it as “nervenkitt” (or nerve putty). This description led to the use of the term “neuroglia,” which derives from archaic Greek, meaning something sticky or clammy. The notion that neuroglia were there merely as neural putty was treated with the reverence usually reserved for a bona fide papal encyclical and as such neuroglia remained sidelined for decades to come. Even though Virchow was responsible for the term neuroglia coming into use, at this stage he did not recognize that it was made up of cells rather than an acellular connective tissue.