Skeletal and smooth muscles move when the nerve impulses sent from the ? stimulate the muscle fibers telling them to either contract or relax

Your dog can sniff at or even eat a bit of catnip. the herb is edible and not harmful. just don't expect them to roll around like a cat would! your dog may scrutinize catnip by licking and smelling at it, or be totally indifferent to this stimulant.

Iwould put 'think' in the blank