Ependymal cell

Also known as: ependyma, ependymocyte, tanycyte, choroid epithelial cell

Cuboidal to columnar ciliated glial cells that line the ventricles of the brain and the central canal of the spinal cord. Modified ependymal cells form the CSF-secreting epithelium of the choroid plexus.

Overview

The ependyma is a single layer of cuboidal to low-columnar epithelial-like cells resting directly on neural tissue; there is no true basement membrane on the brain side. The apical surfaces carry motile cilia that beat in coordinated waves, helping to circulate CSF, and microvilli that absorb fluid. Neighbouring ependymal cells are joined mainly by gap junctions and adherens junctions rather than tight junctions. The ventricular lining is therefore permeable, and CSF exchanges freely with brain interstitial fluid.

Over the choroid plexuses the ependyma is modified into the choroid plexus epithelium. These cells have tight junctions, forming the blood–CSF barrier, along with abundant microvilli, mitochondria, Na⁺/K⁺-ATPase and carbonic anhydrase, and they actively secrete most of the CSF. Tanycytes are specialised elongated ependymal cells in the floor of the third ventricle and the median eminence. Their basal processes reach hypothalamic capillaries and neurons, and they participate in sensing nutrients and hormones and in regulating hypothalamic–pituitary signalling.

Location

Lining of the lateral, third and fourth ventricles, the cerebral aqueduct and the spinal central canal. Choroid epithelium covers the choroid plexuses.

Anatomy

Histology

Simple cuboidal or columnar epithelium with apical cilia (9+2) and microvilli, without goblet cells. The choroid epithelium has a brush border and tight junctions over a core of fenestrated capillaries.

Development

Derived from the neuroepithelium lining the neural tube lumen, by way of radial glia.

Function

Form the lining of the ventricular system and central canal.

Circulate CSF by ciliary beating.

Secrete CSF (choroid plexus epithelium) and form the blood–CSF barrier.

Mediate CSF–brain exchange and hypothalamic hormone and nutrient sensing (tanycytes).

A subventricular stem-cell niche lies just beneath the ependyma of the lateral ventricles.

Clinical significance

Ependymoma

In children it typically arises in the fourth ventricle, causing obstructive hydrocephalus. Histology shows perivascular pseudorosettes and true ependymal rosettes. In adults it is commonly intramedullary in the spinal cord, and the myxopapillary variant arises in the filum terminale.

Ciliary dysfunction

Defective ependymal ciliary motility, as in primary ciliary dyskinesia and some genetic syndromes, has been linked to hydrocephalus. In humans this is much less consistent than in mouse models.