You start an exam and realize that you did not study enough for it. You find it difficult to concentrate because your heart is racing, your stomach seems tied in a knot, you are breathing too quickly, and your mouth is dry. Most likely, you are experiencing the effects of the . You start an exam and realize that you did not study enough for it. You find it difficult to concentrate because your heart is racing, your stomach seems tied in a knot, you are breathing too quickly, and your mouth is dry. Most likely, you are experiencing the effects of the . sensory nervous system central nervous system sympathetic division parasympathetic division