Which structure is at work when the body deals with reflex actions? the heart
the brain stem
the vertebral column
the spinal cord

the cell cycle is the final answer! : )

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.