It’s common for kids to hurt themselves when they’re playing sports or goofing around. Most injuries result in bruised elbows, skinned knees or a bonked head.

Head injuries usually are mild, though you might end up with a “goose egg” for a few days. A goose egg is the result of bleeding that occurs under your scalp but outside your skull. It is a type of injury that doctors refer to as a hematoma (sounds like hee-ma-TOE-ma).

The brain is an amazing organ, but it is vulnerable to injury because it’s soft. (Think of it as a mound of Jell-O inside a bony case.) A concussion is an injury to the brain that results in a temporary loss of normal brain function.

The brain is divided into three main parts. The cerebrum (suh-REE-brum) controls higher mental functions such as thinking, memory, emotions, language and recognizing sensations. The cerebellum (sare-uh-BELL-um) controls balance and coordination. The brainstem controls bodily functions such as breathing, temperature regulation, heart rate and blood pressure.

The brain is surrounded by a number of structures to keep it safe. First, it’s encased in the skull to protect it from outside forces. Second, there are supportive tissues between certain parts of the brain to stabilize it. Finally, it’s covered on all sides by three membranes and a layer of fluid. You could say that the brain “floats” inside the skull.

Despite those safeguards, the brain can still be injured. If you fall, your skull and brain are traveling in the same direction at the same speed. When you hit the ground, your head stops instantly, but the brain continues to move forward and strikes the inside of your skull. When that happens, part of the force of the fall is transferred to your brain. Because the brain is soft, it will briefly deform as it hits the inside of the skull. (Imagine shaking Jell-O in a bowl.)

If you’re standing still and get hit by a soccer ball or someone’s elbow, the same action occurs in reverse. In that case, your skull will be pushed in one direction while your brain is forced in the other.

The symptoms of a concussion vary from person to person, but the most common ones are prolonged headache, dizziness, confusion, nausea or vomiting, fatigue and memory problems. You don’t have to lose consciousness to have a concussion, but you might not remember what happened right before or after the injury.

The best way to treat a concussion is to prevent it from happening in the first place. That’s why your parents bug you to be careful and wear a helmet when you play certain sports or ride a bike.

But accidents do happen. If you hit your head and develop symptoms of a concussion, the most important thing to do is to tell an adult what’s going on! The worst thing to do would be to continue playing, because that increases the risk of either delaying your recovery or having a second injury, which could be more serious.

Howard J. Bennett

Bennett is a Washington pediatrician. His Web site, www.howardjbennett.com, includes past KidsPost articles and other cool stuff.