Answer: Ventricles are fluid filled cavities where cerebrospinal fluid is produced.
From https://cdminny.blogspot.com/2014/03/wiltims-121-left-at-albuquerque.html
The choroid plexus is a series of modified ependymal cells in the ventricular system that produces cerebrospinal fluid (CSF.) The CSF serves to cushion and insulate the brain, keeping it buoyant inside the skull. The average volume of CSF in the brain is 150-250 mL. Without the buoyant forces helping to keep the brain afloat, the brain would crush itself under its own weight as it rests against the base of the skull.
The brain has 4 ventricles. The two largest and dorsal most are the lateral ventricles, one in each hemisphere. They connect in the middle and are continuous with the smaller and medially-located third and fourth ventricles. The cerebral aqueduct connects the third and fourth ventricles, while the central canal connects the fourth ventricle with the spinal column.
Hydrocephalus is a medical condition that is defined by enlarged ventricles, which causes the skull to expand in childhood. The increased intracranial pressure may result in developmental deficits.
