Ependyma

EPENDYMA (ependyma), a single-layer cellular lining covering the inner surfaces of the brain's ventricles and channels. Ependymal cells are related to glia and in the mature brain maintain a connection with it (pseudoepithelium).-Origin. The neural tube of the embryo initially has an epithelial structure. With the further growth of its cells, their differentiation also proceeds. A neuroblastoid generation appears, giving rise to nerve cells and fibers. At the same time, the remaining cellular mass of the neural tube forms a protoplasmic-reticulum framework from spongioblasts. The larger part of these subsequently transforms into various types of glial cells, while a portion of them, remaining on the inner surface of the neural tube, permanently retains primary epithelial characteristics. They undergo a peculiar differentiation and become E.-Structure. In the mature brain of an adult, E. cells have a cylindrical or cubic shape. Their basal processes connect with the glial mass. On their free surface, they are provided with hairs; the latter are analogous to cilia and before their emergence from the cell, near the surface, they are equipped with a granular apparatus (basal bodies); the roots of the hairs penetrate deeper, into the region of the nucleus (Vonwiller). Not all cells have cilia. In the protoplasm of the cells, a reticular structure can be seen, sometimes granularity and inclusions. Function. Besides the covering-ciliary function, E. cells also have a secretory function (Fuchs), although this certainly has a subordinate significance (in granular cells devoid of hairs). Furthermore, they have the ability to absorb various soluble substances (Klestadt), i.e., they also have a resorptive function. Additionally, in the spinal and medulla oblongata, E. serves as a support for special intrapendymal nerve cells. The latter direct one of their processes toward the free surface of E. and even protrude it into the lumen of the canal (in lower vertebrates). According to Agduhr, this is the receptor part of a complex apparatus for regulating brain pressure. EPENDYMITIS (ependymitis), inflammation of the ependyma; however, this name is applied not only to inflammatory changes of E. True ependymitides are purulent ependymitides, tuberculous ependymitides, as well as rare lesions of E. of unknown etiology in the form of nodules from granulation tissue, sometimes with giant cells. Seikel described ulcerative ependymitis (e. ulcerosa) of the lateral ventricles of the brain in congenital syphilis. But ependymitides are also called destructive changes of the subependymal glia and ependyma, leading to a change in the smooth ependymal surface of the brain. The most common type of such changes is granulations of E. (so-called ependymitis granularis). Here we are dealing with multiple local proliferations of subependymal glia, sometimes with the participation of cells of Rio-Hortega; the E. cells at the same time also proliferate abnormally, sinking into the depth of the tissue like glandular formations. Macroscopically, E. loses its smooth surface; the areas of glio-ependymal proliferations appear as translucent nodules, giving the entire surface a shagreen-like appearance. Granulations of E. can also appear on the walls of the ventricles and in the channels; sometimes they are concentrated only in limited areas, e.g., in the recessus lat. ventr. IV. When the granulation-altered walls of the ventricles come into contact (e.g., in the horns), adhesion between them may occur. Granulations most frequently occur in hydrocephalus, especially in progressive paralysis, in tumors, partly in senile brain atrophy. In their genesis, increased pressure and enhanced absorption of fluid through E. play the main role. Besides granulations, flat scattered thickenings (scleroses) or reticular whitish formations may appear on the ependymal surface, based on the same glial proliferation. The ependymal surface appears rough and hardened. They are observed in multiple sclerosis.

P. Snesarev.