Morphology of the Nerve Cell (Continuation)
Mode of termination of dendritic processes.—In the last chapter we described the dendritic processes as relatively thick appendages with rough surface, bifurcated several times and terminated in the same gray focus where the cell body of origin resides. B
- PDF / 4,502,338 Bytes
- 31 Pages / 481.89 x 691.65 pts Page_size
- 17 Downloads / 218 Views
MODE OF TERMINATION OF DENDRITIC AND AXONAL PROCESSES.INTERCELLULAR CONNECTIONS
Mode of termination of dendritic processes.-In the last chapter we described the dendritic processes as relatively thick appendages with rough surface, bifurcated several times and terminated in the same gray focus where the cell body of origin resides. But, how is this termination realized? We have referred to Gerlach's opinion in the historic survey on methods. Let us recall here that according to this author, [who initiated the use of carmine as a staining method], there is a dense network resulting from the anastomoses of dendrites, and the fusion of these with the branching of sensory fibers. This dictum, although not based on any conclusive observation, ruled in Science for many years. The reason for this situation was the almost impossible task of replacing such a concept by a seemingly more acceptable law, due to the poverty of analytical methods. Or, moreover, its compatibility with the physiologic postulates of the day, which required the protoplasmic continuity among nerve cells to explain easily the course of nerve impulses through the gray matter. We owe to Golgi the service of having refuted definitively Gerlach's error, demonstrating for the first time and with strong evidence the free termination of the last dendritic branches. Golgi's assertions were confirmed by many authors, such as Mondino, Fusari, Sala, Tartuferi and Lugaro, all disciples of the scholar of Pavia, as well as Forel, His, Kolliker, Hansen, Lenhossek, Retzius, Van Gehuchten, Schaffer, Held, Edinger, Azoulay, Cl. Sala, P. Ramon, Calleja and ourselves, among other scientists outside Italy. [Spines.-] It is important to recognize certain morphologic details on studying dendrites with the Golgi method, because it is possible that in time they will reach physiologic significance. One such a feature is the presence of certain short appendages or collateral spines, emerging at right angles from the surface of dendritic processes and ending in a round or ellipsoidal enlargement. These spines, first mentioned by us in our pUblications on the cerebrum and cerebellum (Cajal, 1891a), have been confirmed by Retzius (1891a), Schaffer (1892), Edinger (1893a), Azoulayl, Berkley (1895), Monti (1895b), [Stefanowska (1897b), Demoor (1896b), as well as Shikishi Hatai (1903) who used a special staining method with acid fuchsin]. They are seen particularly well in dendritic branches of cerebellar Purkinje cells (Fig. 13), as well as in pyramidal cells of the cerebral cortex (Fig. 12). Their number, length and thickness vary in S. R. y Cajal, Texture of the Nervous System of Man and the Vertebrates © Springer-Verlag/Wien 1999
54
Morphology of the Nerve Cell
the various cellular types. They are short, thick and numerous in Purkinje cells, and fine and long in cortical cells. [They vary also with the animal species, and we may state in general terms, that a cell with spiny processes in homologous nuclei has more spines, the higher the level of the subject in the animal ser
Data Loading...
