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.

Question

Quizplus · Accepted Answer

Dopamine cannot directly cross the blood-brain barrier into the brain, making it impossible for injected dopamine to reach the depleted dopamine levels in the brain. The blood-brain barrier is a protective layer of cells surrounding the brain that prevents most foreign substances from entering the brain tissue. Therefore, injecting dopamine into the bloodstream would not have any effect on the symptoms of Parkinson's disease.

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