Final answer:
Choroid epithelial cells produce cerebrospinal fluid (CSF), which circulates through the CNS, supplies nutrients, and protects the brain and spinal cord.
Step-by-step explanation:
The function of choroid epithelial cells, which differentiate from ependymal cells, is to produce cerebrospinal fluid (CSF). The choroid plexus, consisting of a network of these cells lined around blood capillaries, is responsible for filtering blood to make CSF. This fluid circulates through the central nervous system (CNS), providing it with nutrients, removing waste products, and acting as a cushion to protect the brain and spinal cord. Moreover, the tight connections between the ependymal cells, which form a part of the blood-brain barrier (BBB), help to maintain the chemical environment necessary for proper neural functioning.