Circulation

 Ventricular system

  Lateral Ventricles

Although the choroid plexus produces between 50-70% of the total CSF volume (~500ml a day), the ventricle walls and surrounding blood vessels contribute significantly to the production of the fluid. The ventricles are the spaces inside the brain which contain CSF. There are four ventricles in total; the first two are named the lateral ventricles due to their position adjacent to each other (one in each hemisphere of the telencephalon). The lateral ventricles are the largest and most superior of the ventricles. The lateral ventricle has 3 horns:

• The anterior horn extends into the frontal lobe.
• The posterior horn extends into the occipital lobe.
• The inferior horn extends into the temporal lobe.

The volume of the lateral ventricles increases with age, however there is evidence that suggests patients with schizophrenia have enlarged lateral ventricles. The ventricles are lined with ependymal epithelia, and a substantial choroid plexus (see Production section) is located in the Superior portion of the inferior horn of the lateral ventricles.

  Third Ventricle

The third ventricle lies inferiorly to the lateral ventricles, acting as a cleft between the two thalami, and is considered a structure of the diencephalon. The third ventricle is connected to the lateral ventricles by the interventricular foramina (foramina of monro). There are two crescent shaped foramen (each running from the inferior medial aspect of a lateral ventricle to the anterior of the third ventricle) that carry CSF from the lateral ventricles to the third ventricle. Both the third ventricle and the interventricular foramina are lined by ependymal epithelia. The superior part of the third ventricle also contains a choroid plexus (see Production section).

  Fourth Ventricle

The fourth ventricle forms a diamond shape and lies immediately anterior to the cerebellum, and the cerebella peduncles form the lateral walls of the fourth ventricle. This ventricle is located in the pons of the upper medulla. Fluid flows from the third to the fourth ventricle via the cerebral aqueduct (which lies in the mesencephalon). Both the cerebral aqueduct and fourth ventricle are lined by ependymal epithelia. However a choroid plexus (see Production section) is only present close to the bottom of the cerebellum within the fourth ventricle. A video showing the production and flow of cerebrospinal fluid through the ventricular system and subarachnoid space can be seen below.

Flow of cerebrospinal fluid video courtesy of YouTube free of copyright.

   Subarachnoid Space

Cerebrospinal fluid flows into the subarachnoid space (see Homepage) through a number of foramina which extend from the fourth ventricle. There are two lateral apertures known as the luschka foramina which allow CSF to flow from the lateral recess of the fourth ventricle into the subarachnoid space. There is also a single median aperture known as the foramen of magendie allowing CSF to exit the fourth ventricle and flow into the cisterna magna (space between the cerebellum and pons; part of the subarachnoid space). Once in the subarachnoid space the cerebrospinal fluid is free to flow between the trabeculae (which anchor the pia mater and arachnoid membrane together). Because the pia mater descends into the sulci and cisterna of the brain the CSF is able to bathe and protect the whole surface area of the brain.

  Central Canal

The central canal runs longitudinally down the length of the spinal cord. It is supplied with cerebrospinal fluid at its superior end by the fourth ventricle via a point at which the ventricle narrows known as the obex. The obex marks the point at which the brain becomes the spinal cord, and is located in the caudal medulla. The central canal closes off with age and represents the adult remainder of the neural tube. CSF can be removed from the central canal via a lumbar puncture.