Which type of cell in the central nervous system (CNS) plays a key role in determining capillary permeability and maintaining the blood-brain barrier?

• A. Oligodendrocytes
• B. Astrocytes
• C. Microglia
• D. Ependymal cells

Answer: (B)

Verified step by step guidance

1. Understand the role of the blood-brain barrier (BBB): The BBB is a selective barrier that protects the brain from harmful substances in the blood while allowing essential nutrients to pass through. It is formed by endothelial cells of capillaries, but its function is heavily influenced by surrounding cells in the CNS.
2. Review the function of astrocytes: Astrocytes are star-shaped glial cells in the CNS that play a critical role in maintaining the BBB. They release signaling molecules that regulate the tight junctions between endothelial cells, which control capillary permeability.
3. Differentiate astrocytes from other CNS cells: Oligodendrocytes produce myelin for insulating axons, microglia act as immune cells in the CNS, and ependymal cells line the ventricles and produce cerebrospinal fluid. None of these directly regulate the BBB like astrocytes do.
4. Connect astrocytes to capillary permeability: Astrocytes' end-feet surround capillaries and influence the permeability of the endothelial cells, ensuring that only specific substances can cross into the brain.
5. Conclude that astrocytes are the key cell type in the CNS responsible for determining capillary permeability and maintaining the blood-brain barrier.