Ependyma
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Ependymal cells are derived from the early germinal epithelium lining the lumen of the neural tube and thus are also ectodermal derivatives (along with neurons, astrocytes, and oligodendrocytes). Ependymal cells line the ventricles of the brain and the central canal of the spinal cord. They are arranged in a single-layered columnar epithelium, and have many of the histological characteristics of simple epithelium, which vary from squamous to cuboidal depending upon their location. The ependyma forming the ventricular lining do not connect to a basal lamina, but rest directly upon underlying nervous tissue. As shown in Figure 8.17, the surface facing the ventricle contains many microvilli and cilia. These cilia move cerebrospinal fluid (CSF) in the ventricles. The lateral borders of the ependymal cells are relatively straight and form junctions with adjacent cells.
Ependymal cells are modified in various regions of the ventricles into layers of cuboidal epithelium, which do lie on a basement membrane (formed by an outgrowth of the pia) over a rich bed of vasculature and connective tissue. This is the choroid plexus studied in the Laboratory that is responsible for the secretion, uptake and transport of substances to and from the CSF.
Figure 8.17 |
