Paul, Sato, aged 9, of Brigham City, Utah, for his question:

What makes the heart beat?

Run and ,dump for a while, and the heart beats faster. It may even speed up from excitement during a hair‑raising movie. During sleep, when the brain and body are resting, the heart beat slows down. Certain nerve cells cause the heart to speed up and slow dawn. These cells lead from the heart to the nervous system.

However, these nerve cells do not connect with your thinking brain. You cannot will, or order your heart to beat faster or slower, Neither can you order it to beat or atop beating. The heart carries on without consulting your brain,

The heart itself takes care of each beat. Each heart beat is caused by a small bundle of nerves right within the heart itself. These nerves begin and end in the heart. Other nerve cells may speed up or slow down the heart beat. But if left to themselves, the heart’s own nerves will keep it beating with a steady rhythm.