It's midnight and you are alone in your room studying. you hear a loud crash outside your room. your body instantly reacts to this potential threat as you feel your heart pounding and your senses sharpening. then you see your lumbering english sheep dog walking around the hallway corner and realize that the crash was undoubtedly from something he knocked over. recovering from your alarm, your body now relaxes and you return to normal. the body system you to return to normal is the