All amphetamines are known to increase muscle tone. This includes all manner of muscles including the bladder sphincter, and arteriole walls, causing raised blood pressure. I'ts probably because the body responds to adrenalin (very similar in structure to amphetamines) in this way because of the so-called "fight or flight response". All these effects combine to make sure the body doesn't have to worry about any of the usual things such as urination, hunger etc, and can just concentrate on getting the hell away from that lion!
The stimulation of the trigeminal nerve will increase muscle tone in the areas that nerve controls. The vagus nerve will be stimulated in a similar way, increasing tone in the torso.