Ventricles and The Meninges

The circulation of CSF:

- The choroid plexus of each ventricle produces CSF. - CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures in the walls of the fourth ventricle. The long cilia of the ependymal cells lining the ventricles help keep the CSF in constant motion. - CSF flows through the subarachnoid space. - CSF is absorbed into the dural venous sinuses via the arachnoid villi at the top of the skull.

The formation of CSF:

CSF is formed by the choroid plexuses. Each choroid plexuses consists of a knot of porous capillaries surrounded by a single layer of ependymal cells joined by tight junctions and bearing long cilia. Fluid leaking from porous capillaries is processed by the ependymal cells to form the CSF in the ventricles.

The purpose of CSF:

CSF is found in and around the brain and spinal cord. It forms a liquid cushion that gives buoyancy to the CNS structures. By floating the jelly-like brain, the CSF effectively reduces brain weight by 97% and prevents the delicate brain from crushing under its own weight. It also protects the brain and spinal cord from blows and other trauma. Furthermore, although the brain has a rich blood supply, CSF helps nourish the brain, and there is some evidence that is carries chemical signals (such as hormones and sleep- and appetite-inducing molecules) from one part of the brain to another. In adults, total CSF volume is about 150 ml and is replaced every 8 hours or so.

The reabsorption of CSF:

CSF is reabsorbed into the blood at the by the arachnoid villus in the dural sinuses.

Arachnoid Villi

Knoblike projections of the arachnoid mater protrude superiorly through the dura mater and into the superior sigittal sinus. These _______ absorb cerebrospinal fluid into the venous blood of the sinus.

Subarachnoid Space

Spider-web-like extensions span this space and secure the arachnoid mater to the underlying pia mater. This space is filled with cerebrolspinal fluid and also contains the largest blood vessels serving the brain. Because the arachnoid mater is fine and elastic, the blood vessels are poorly protected.

Choroid Plexus

The ____ ______ hangs from the roof of each ventricle forming cerebrospinal fluid (CSF). These plexuses are fond-shaped clusters of broad, thin-walled capillaries enclosed first by pia mater and then by a layer of ependymal cells lining the ventricles.

The four Ventricles of the brain include:

The lateral ventricles, the third ventricle, and the fourth ventricle. Located illustrated is attached picture.

Arachnoid Mater

The middle meninx forms the loose brain covering, never dipping into the sulci at the cerebral surface. It is separated from the more superficial dura mater by a narrow serous cavity, the subdural space, which contains a film of fluid. Beneath this membrane is the subarachnoid space

Pia Mater

This "gentle mother" layer is composed of delicate connective tissue and richly invested with tiny blood vessels. It is the only meninx that clings tightly to the brain like cellophane wrap, following its every convolution. Small arteries entering the brain tissue tissue carry ragged sheaths of pia mater inwards with them for short distances.

Dura Mater

This leathery "tough mother" is the strongest meninx. Where it surrounds the brain, it is a two-layered sheet of fibrous connective tissue. The most superficial layer periosteal layer attaches to the inner surface of the skull. The deeper meningeal layer forms the true external covering of the brain and continues caudally in the vertebral canal as the spinal dura mater.