The ventricular system of the brain consists of a continuous communicating system of five fluid-filled cavities whose inner walls are lined with ependymal cells. Each ventricle possesses a choroid plexus (see p. 17). The cavities are numbered and comprise the cerebral aqueduct, the unpaired third and fourth ventricles, and the paired lateral ventricles.
The fourth ventricle is a roughly pyramid-shaped cavity that is bounded ven-trally by the medulla and pons and its floor is called the rhomboid fossa. The roof of the ventricle is incomplete and is formed from the anterior medullary velum and the posterior medullary velum (see also p. 17). The apex passes upward into the cerebellum at a point called the apex or fastigium. Cerebrospinal fluid (CSF) can flow from the fourth ventricle into the subarachnoid space through two apertures. The foramen of Luschka is an opening of the lateral recess into the sub-arachnoid space in the region of the cere-bellar flocculus. There is a more important aperture, the foramen of Magendie, which lies caudally in the ventricular roof. Most of the CSF outflow from the ventricle occurs via this aperture.
From the fourth ventricle a narrow channel called the cerebral aqueduct runs into the third ventricle. This is a relatively narrow channel that runs between the two medial walls of the diencephalon. The roof of the ventricle consists of a tela choroidea and a lining of ependyma and pial cells, from which a choroid plexus protrudes into the cavity of the ventricle. The medial walls of the paired thalami form most of the walls of the third ventricle, and the hypothalamus supplies the floor and the basal part of the lateral walls. Rostrally, the boundary of the third ventricle is defined by the lamina terminalis and the anterior commissure. At the rostral end there is a small extension of the ventricle called the optic recess, and there is a small downward extension called the infundibular recess where the infundibulum extends downwards towards the pituitary gland.
The third ventricle communicates with the lateral ventricles though two inter-ventricular foramina, or foramina of
Monro. These are apertures between the anterior end of the thalamus and the column of the fornix. The lateral ventricles are the largest of the ventricles, and have a paired, irregular appearance. On each side there are anterior and posterior horns and a central body. The roof of the anterior horns is formed by the corpus callosum and its medial wall by the septum pel-lucidum. Each lateral wall and the floor is supplied by the head of the caudate nucleus. The body extends rostrally from the interventricular foramina to the splenium of the corpus callosum. The corpus callo-sum forms the roof of the body portion, and the floor is contributed to by a number of structures, these being from lateral to medial the caudate nucleus, vena terminalis, stria terminalis, thalamus, choroid plexus, and fornix. The posterior horn extends caudally into the occipital lobe; its roof is formed by part of the corpus callo-sum.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.