What structure is responsible for the formation of cerebrospinal fluid?

The choroid plexus is the structure responsible for the formation of cerebrospinal fluid (CSF). This specialized tissue is found within the ventricles of the brain and consists of a network of blood vessels and ependymal cells. The ependymal cells, which line the ventricles, actively filter blood plasma to produce CSF. This fluid serves several vital functions, including cushioning the brain, maintaining intra-cranial pressure, and facilitating the exchange of nutrients and waste products between the brain and blood.

While the subarachnoid space is a region where CSF circulates, it does not play a role in its production. The ventricles are filled with CSF, but they are not the source of its formation; rather, they house the choroid plexus. The pineal gland is involved in the production of melatonin and does not have any direct role in cerebrospinal fluid production. Hence, the choroid plexus is the correct answer as it is the primary site for CSF synthesis.