It is a nervous system outside the brain and the spinal cord
Answer:
Receptors
Explanation:
So this is a poorly put question, and very vague, but within the context, it sounds to be either Receptors or Hormones. Receptors are cells, so I would go with that.
But this makes no sense.
Answer:
Because they don't use a variety of muscles as much as they could by doing more sports so when they use the lesser used muscles, they could get hurt.
Explanation:
Opiates. highly addictive drugs with very bad side affects