What is the choroid plexus?

• A. An outer layer of the skull
• B. A nerve plexus in the hippocampus
• C. A network of capillaries and specialized cells in the ventricles
• D. A fluid-filled cavity

Answer: (C)

The main concept here is that the choroid plexus is the tissue inside the brain that produces cerebrospinal fluid. It is a specialized network of capillaries surrounded by ependymal cells that line the ventricles. This arrangement sits within the ventricular system (lateral, third, and fourth ventricles) and forms part of the blood–CSF barrier. From these capillaries and cells, CSF is made and then circulates around the brain and spinal cord. So it’s not an outer skull layer, not a nerve plexus, and not merely a fluid-filled cavity—the choroid plexus is the vascularized tissue inside the ventricles responsible for generating CSF.