The brain contains many specialised structures that work together. Among them are four connected spaces known as the cerebral ventricles. They are found within the cerebrum and brainstem and form part of a larger system that supports the central nervous system.

The ventricles contain cerebrospinal fluid, a clear fluid that helps cushion the brain and spinal cord, maintain a stable chemical environment, and transport useful substances while waste is cleared.

The ventricular system

The ventricular system is made up of two lateral ventricles, the third ventricle, the cerebral aqueduct, and the fourth ventricle. These spaces are linked so CSF can move through the brain and into the surrounding subarachnoid spaces.

Choroid plexus

The choroid plexus is a specialised network of blood vessels and cells located in the ventricles. It produces much of the CSF and helps regulate what passes between the bloodstream and the fluid surrounding the brain.

Choroid plexus is found in the lateral, third, and fourth ventricles, but not in the cerebral aqueduct. The ependymal cells associated with it contribute to the lining and fluid-producing interface.

Lateral ventricles

The lateral ventricles are the largest ventricular spaces. There is one in each cerebral hemisphere, and each has a curved, roughly C-shaped form. Their parts include the frontal horn, body, atrium, temporal horn, and occipital horn.

The two lateral ventricles connect with the third ventricle through the interventricular foramina, also called the foramina of Monro. CSF passes through these narrow openings as it continues along its route.

Third ventricle

The third ventricle is a narrow cavity positioned near the centre of the brain, between the two sides of the diencephalon. The thalamus and hypothalamus form much of its surrounding region.

CSF enters the third ventricle from the lateral ventricles and then continues toward the cerebral aqueduct.

Cerebral aqueduct

The cerebral aqueduct is a slender channel connecting the third and fourth ventricles. It is also known as the aqueduct of Sylvius. Because the channel is narrow, disruption of CSF flow here can affect pressure within the ventricular system.

Fourth ventricle

The fourth ventricle lies between the brainstem and cerebellum. It continues downward toward the central canal of the spinal cord and opens into the subarachnoid space through several openings.

From there, CSF can circulate around the brain and spinal cord. The surrounding cisterns are widened areas of the subarachnoid space that help distribute the fluid.

The cerebrospinal fluid pathway

From production to absorption

A simplified pathway begins in the choroid plexus of the lateral ventricles. CSF moves through the interventricular foramina to the third ventricle, passes through the cerebral aqueduct, and reaches the fourth ventricle.

It then leaves the ventricular system through openings into the subarachnoid space, where it circulates around the brain and spinal cord. CSF is eventually returned to the bloodstream through structures associated with the dural venous sinuses and through lymphatic routes.

This movement is continuous: fluid is produced, circulated, and absorbed so the nervous system can remain supported and protected.

Key points

• The cerebral ventricles are connected spaces inside the brain.
• The choroid plexus produces much of the cerebrospinal fluid.
• CSF cushions the brain and spinal cord and helps maintain a stable environment.
• The lateral ventricles connect to the third ventricle, which connects to the fourth through the cerebral aqueduct.
• After leaving the fourth ventricle, CSF circulates around the brain and spinal cord before being absorbed.