Question

which glial cell insulates nerve fibers from extracellular fluids and speeds up signal conduction in the brain?
oligodendrocyte
schwann cell
ependymal cell
astrocyte

Explanation:

Oligodendrocytes are glial cells in the central nervous system (brain and spinal cord) that form myelin sheaths around nerve fibers, insulating them from extracellular fluids and increasing the speed of signal conduction. Schwann cells do a similar job but are in the peripheral nervous system. Ependymal cells line the ventricles of the brain and spinal - cord central canal and are involved in cerebrospinal fluid production and circulation. Astrocytes have multiple functions including providing support to neurons and maintaining the blood - brain barrier, but not insulation for faster signal conduction.

Answer:

Oligodendrocyte