Pia Mater
This is the 3 rd and deepest layer which is closely adherent to the brain. It is also very fine and delicate and follows the convolutions of the brain. Many blood vessels pass through this thin layer to supply the brain.
THE VENTRICULAR SYSTEM
The ventricular system is composed of the interconnected cavities within the brain which contain the cerebrospinal fluid . The ventricles of the brain include: 2 lateral ventricles (one in each hemisphere), a 3 rd ventricle (diencephalon) and the 4 th ventricle (hindbrain). The 2 lateral ventricles communicate with the 3 rd ventricle via the interventriular foramina. The 3 rd ventricle communicates with the 4 th ventricle via the cerebral aqueduct. The 4 th ventricle gradually narrows caudally to become confluent with the central canal of the spinal cord. The ventricular system communicates with the subarachnoid space by means of 3 openings in the roof of the 4 th ventricle; 2 lateral apertures and 1medial aperture. The 2 lateral ventricles are the largest. These are located respectively in the frontal, parietal, occipital and temporal lobes of the cerebral hemispheres. The 3 rd ventricle is a perpendicular slit between the 2 thalami. The cerebral aqueduct is a short tubular canal that passes through the midbrain and connects the 3 rd & 4 th ventricles. The 4 th ventricle lies between the cerebellum dorsally and the dorsal aspect of the pons and medulla oblongata ventrally.
The ventricular system and the central canal of the spinal cord are lined by ciliated ependymal epithelium or ependyma.
Production of Cerebrospinal Fluid
Cerebrospinal fluid (CSF) is produced by the choroid plexuses of the ventricular system.
There is continual turnover of CSF. There is evidence that it is produced at a constant flow rate despite the pressure of CSF in the ventricular system. The rate is independent of the hydrostatic pressure of the blood but is influenced by the osmotic pressure of the blood.
Circulation of CSF
The CSF is produced in the ventricles, circulates to the subarachnoid space and is absorbed into the venous sinus.
Beginning in the lateral ventricles, CSF produced in the choroid plexuses passes through the interventricular foramina to the 3 rd ventricle. Here, the choroid plexus of the 3 rd ventricle adds
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