Many Medications Introduced into the Bloodstream Cannot Directly Affect the Neurons

Multiple Choice

Many medications introduced into the bloodstream cannot directly affect the neurons of the CNS because

A) oligodendrocytes form a continuous myelin sheath around the axons.
B) the astrocytes isolate the CNS by forming a blood-brain barrier.
C) the neurilemma is impermeable to most molecules.
D) ependymal cells restrict the flow of interstitial fluid between the capillaries and the neurons.
E) Schwann cells form a capsule around neurons.