Why do you get knots on your head if you bump your head?


Question:
Why do you get knots on your head if you bump your head, but if you pump your arm or leg, you usually only get a bruise? What is the physical difference between the head and other parts of the body that causes this unique reaction to an injury?

Answers:
It's not a knot on your head, it really is a bruise. A bruise anywhere on your body is blood leaking out from the injured blood vessels in the area. The blood pools and coagulates. Over time, the white blood cells will break down the mass and the bruise will disappear. The difference is the amount of space there is for the blood to pool in. On your head, the skin is very close to the bone of your skull. There aren't any muscles there to allow the blood to pool. So, the blood sort of bulges out. No, puncturing the knot on your head won't mean that you will have a fountain of blood spurting out ! ( you are watching too many horror films ! ) The pooling blood is near the broken blood vessels which lie along the skull, or in a very bad head injury, in the meninges.

Other Answers:
I do sometimes get knots on other bruises.
Because there is no tissue to hide the swelling on the top of the head.... where as you have lots more tissue to spare in the muscles. You actually do get a knot in the muscles... but the swelling isn't as confined and it disperses earlier than those that are trapped in the very specific membranes that cover your head. The membranes are limited by what are called suture lines in the skull, and that is why the swelling happens.
The difference is hard bone vs soft tissue is my guess
I have knots on bruises on my arms and legs. It depends on where the vein is. You have more veins around your brain than other muscles.
Why do men have to deal with a big sack full of balls hanging between their legs?(strait men that is)
There is no where for the swelling to go on your head except out because your skull is behind it. If you bump your arm some of the impact is absorbed by the muscle tissues (think about punching a brick wall through a pillow...your arm...and then without the pillow...your head). Your head has no cushioning and also no room for the blood to pool...hence the goose egg. The same thing tends to happen on the shin.
If you get an injury anywhere, it could swell up. But your skull only allows itself to swell outward in order to protect your brain tissue.
There are large bones there that keep the swelling from spreading to a different spot.


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