Deep inside the human brain are the hollow fluid-filled cavities called ventricles.

There are two lateral ventricles, one in each cerebral hemisphere.

These lateral ventricles have three distinct projections — the anterior, the inferior and the posterior horns visible from the lateral side.

At the anterior side, a thin membrane called the septum pellucidum separates these two ventricles.

Through a channel called the interventricular foramen, each lateral ventricle is connected to the slender third ventricle located in the diencephalon.

Posterior to the third ventricle is the canal-like structure — the cerebral aqueduct, which connects it to the fourth ventricle located between the pons and the cerebellum.

Brain ventricles are filled with cerebrospinal fluid, or CSF, produced and filtered from a network of blood capillaries called the choroid plexus.

These capillaries are lined by tightly joined ependymal cells that secrete the CSF into the ventricles, which drain into the central canal of the spinal cord and also surround the brain.

CSF mainly provides mechanical protection to the CNS, enables optimal neural signaling, and acts as a medium for nutrient exchange.