A Person with Parkinson's Disease Experiences Severe Difficulty in Initiating

Multiple Choice

A person with Parkinson's disease experiences severe difficulty in initiating movement due to the depletion of the chemical dopamine in the brain.Injecting dopamine into this person's bloodstream has no effect on the symptoms because

A) the body recognizes that the injected dopamine is artificial.
B) dopamine cannot directly cross the blood-brain barrier into the brain.
C) myelin insulates neurons from foreign substances in the bloodstream.
D) this substance cannot be transported into the brain by the sodium-potassium pump.