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

The answer to the question above is this: the endothelium of CNS capillaries forms a blood-brain barrier. The blood-brain barrier is actually a mechanism that the capillaries that carry blood to the central nervous system can do. What this barrier does is that it filters and only allows certain substances (and not all), that's why this cannot directly affect the neurons in the central nervous system.

Mitochondria is the cell organelle that produced the energy that is needed in the body system in form of atp, that is why it is called the power house of the cell. energy is needed by the living organisms to carry out the activities which sustain life.  if the mitochondria is destroyed atp will not be produced. if the mitochondria is destroyed, energy production will stop and the affected living organism will not have the energy to carry out the necessary life processes; this will lead to the death of the organism.