Mr. lopez is prescribed oxycodone to manage chronic lower back pain. oxycodone is called an opioid because its action resembles that of the brain's natural painkillers.

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

the correct answer is:

a population changes in response to a change in the environment.