The Directions of Ciliary Beat on the Wall of the Fourth Ventricle in the Mouse

Abstract

Directions of ciliary beat on the wall of the fourth ventricle in the mouse were observed by scanning electron microscopy. The direction of ciliary beat is definite in the ventricle: it is either toward the central canal or toward the lateral apertures of the fourth ventricle. In the anterior half of the fourth ventricular floor, the cilia beat posteriorly in the paramedian part which forms the bilateral banks of the median sulcus but they beat either posteromedially toward the central fovea or posteriorly to posterolaterally toward the lateral aperture in the more lateral part. The central fovea is connected to the central canal by a channel-like groove which coincides with the median sulcus of the posterior half of the floor. In the area immediately lateral to anterolateral to the central fovea, the cilia beat anteriorly, anteromedially to medially like a swirl. In the anterior part of the posterior half of the floor which corresponds to the bar of the letter“T, ”most of the cilia in the more medial part except the median part beat anterolaterally, anteriorly or even anteromedially but the cilia in the more lateral part beat laterally toward the lateral aperture. In the narrow posterior process of the posterior half of the floor the cilia in the paramedian banks along the channel-like groove as well as the cilia in the bottom beat posteriorly toward the central canal, while the cilia in the more lateral margin beat anteriorly toward the reverse direction, but this is thought not contradictory to the current of the cerebrospinal fluid. The roof of the fourth ventricular area was divided into two parts: the wall of the recess of the inferior colliculi which consists of the posterior continuation of the cerebral aqueduct and the anterior part of the superior medullary velum, and the roof of the fourth ventricle proper consisting of the posterior part of the superior medullary velum, the inferior medullary velum and the choroid plexus of the fourth ventricle. The surface of the posterior continuation of the cerebral aqueduct and the superior and inferior medullary vela are covered with numerous cilia except in the midline and the directions of ciliary beat seem to be generally in accordance with those on the floor.
These observations suggest that the ciliary beat elaborately regulates the directions of cerebrospinal fluid flowing in the ventricle. The funnel-like shape of the fourth ventricular floor is also thought a factor to produce a smooth flow of the fluid.