The brain doesn’t completely fill the skull so, when Tom hits his head, his brain bounces around and gets bruised. If it bounces around really hard, it bleeds.
The sac that holds the brain together is called the dura and it has 3 layers. When there’s a bruise on the layer closest to the brain, it’s called a subdural hematoma.
The outside of the skull is smooth, but the inside has small bony protrusions that snag the brain.
If the bony protrusions from the skull pierce the dura and tear the brain, the bleeding causes swelling. Pieces of the skull are temporarily removed to allow the brain to swell to avoid more bleeding.
Now that you know these facts, make sure Tom has a solid helmet for activities where he might bounce his brain.
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