What Happens to Your Brain When You Hit Your Head — Transcript

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1. 0:00When you hit your head hard, the skull
2. 0:02stops almost instantly, but the brain
3. 0:04inside it keeps moving.
4. 0:06It floats in a layer of fluid, so for a
5. 0:09few thousandths of a second, it travels
6. 0:11on at the speed your head had before the
7. 0:13impact. Then, it hits the inside of the
8. 0:16skull right under the point of impact.
9. 0:19This is the coup. The surface of the
10. 0:22brain is crushed against the bone, and
11. 0:24the tissue there is bruised.
12. 0:27The brain does not stop there. It
13. 0:29bounces back through the fluid and
14. 0:31strikes the opposite side of the skull.
15. 0:33This is the contrecoup. It is often the
16. 0:36more damaging of the two because the
17. 0:38inside of the skull is not smooth. The
18. 0:41front and the base have bony ridges, and
19. 0:43the brain scrapes across them as it
20. 0:45hits.
21. 0:46The brain also twists as it moves.
22. 0:49Between the brain and the membrane under
23. 0:51the skull run thin veins, and when the
24. 0:54brain shifts, these veins can stretch
25. 0:56and tear.
26. 0:58Small blood vessels inside the brain
27. 1:00tissue tear, too, at both impact sites.
28. 1:03Blood leaks out of them into the tissue
29. 1:06and into the space under the skull,
30. 1:08where it collects.
31. 1:10This is where the body's reaction
32. 1:11begins. Damaged cells send out chemical
33. 1:14signals, and immune cells move into the
34. 1:17injured areas to clear away dead tissue.
35. 1:20The blood that has leaked out is broken
36. 1:22down and removed over time. The injured
37. 1:25tissue swells, and because the skull
38. 1:27cannot expand, the swelling raises the
39. 1:29pressure inside it.
40. 1:31The surviving brain cells now have to
41. 1:33repair their stretched membranes and
42. 1:35restore their chemical balance. This
43. 1:38takes a lot of energy, while the injured
44. 1:40areas receive less blood than normal.
45. 1:43This is why you feel dizzy, confused, or
46. 1:45very tired after a blow to the head. The
47. 1:48brain is working at a reduced level
48. 1:50while it recovers.
49. 1:52Over the next hours and days, the
50. 1:54swelling goes down, and the cells return
51. 1:56to normal.