While jotting down the numerous functions of glial cells being rattled off by your professor, you make an error: glial cells do NOT

a. prevent the formation of a myelin sheath around axons.
b. make up a blood-brain barrier around blood vessels in the brain.
c. help guide newborn neurons to appropriate locations in the brain.
d. take up excess neurotransmitters and other substances at the gaps between neurons.

Answer: a. prevent the formation of a myelin sheath around axons.