An adult human brain weighs about 1.5 kgs, but we don’t really feel it weighing us down!
That’s because the brain is cushioned by cerebrospinal fluid or CSF, which can be found within brain cavities called ventricles.
These cavities are involved in the production, transport and removal of CSF, and they are connected to each other. So, as a whole they are often referred to as the ventricular system of the brain.
CSF doesn’t only fill the ventricles, but also the subarachnoid space, which surrounds the brain and spinal cord. This way, CSF cushions and protects the brain from head trauma, and it also provides buoyancy so that the brain doesn’t compress blood vessels and cranial nerve roots against the cranium. It also provides protection against sudden intracranial pressure changes.
CSF can also transport nutrients for nervous tissue,
as well as remove metabolic waste products.
It can also transport hormones, and
influence the brain's excitability by regulating its ionic composition. .
Now, the ventricular system consists of four ventricles: two lateral ventricles, the third ventricle and the fourth ventricle.
CSF flows from the lateral ventricles through the left and right interventricular foramina, also called the foramina of Monro, to the third ventricle.
From here, it passes through the cerebral aqueduct to reach the fourth ventricle. CSF can then flow caudally into the central canal of the spinal cord.