Commentary on “Sulla Fina Anatomia del Cervelletto Umano. Archivio Italiano per le Malatie Nervose 11:90–107.” (English Title: On the Fine Anatomy of the Human Cerebellum)

Abstract

He stated that [3]: [...] always in the granular layer, with the silver nitrate method, I was able to verify not only the beautiful characteristics of the nerve cell that lay within (characteristics that some have denies) but I was also able to depict their exact dimensions, shapes, positions and ramifications [...]. Before Golgi’s study on cerebellum, there were contradictory ideas on the nature of the granule cell layer. Some histologists regarded the cells contained at this level, as “connective” cells (i.e. glial cells). On the basis of the application of the black reaction, which quite easily allowed a differentiation between nerve and glial cells, Golgi was very determined to affirm that “the so-called granules must be generally considered as small nerve cells provided with three, four, five, and sometimes six processes, usually ramified” and that only one of these processes “should be essentially considered a nerve prolongation” (axon) (Fig. 1). The constant presence of a single ramified nervous prolongation (i.e. of a single axon) for every single nerve cell, later confirmed by Golgi as being applicable to all the regions of the central nervous system, is one of his most enduring contributions to neuroscience. In the external layer of the cerebellar cortex, Golgi discovered bundles of fibres which “run parallel to each other and, in most cases, are of considerable length, many of them running around an entire circumvolution” (Fig. 1). Golgi was able to observe that these fibres, now known as parallel fibres, “could be considered as originating from the granule layer” but was unable to fully trace the axons of the granule cells and so his research failed to reveal that the axons in fact ascend toward the most external region of the cortex and then bifurcates in the shape of a T, giving origin to the parallel fibres. This was one of the first important discoveries of Santiago Ramon y Cajal which was made with the aid of the black reaction in 1888 [8]. Furthermore, Golgi described two kinds of “big nerve cells” in the granular layer—the first were “long and narrow cells irregularly fusiform, with a maximum diameter parallel to the surface of the circumvolution” and the others were “irregularly P. Mazzarello (*) Historical Museum of the University and Department of Experimental Medicine, University of Pavia, Pavia, Italy e-mail: paolo.mazzarello@unipv.it