Knocked out by impact. What exactly happened to me?

July 12, 2016 10:48 AM

So this past Sunday I set out on a bike ride with my wife and a friend along the Chicago lakefront and very shortly afterward I took a very bad tumble. I'm okay (bruised, road rashed and a sprained/shocked forearm) but I am mostly curious about what happened to my brain biologically.

I assume I was knocked out like Buster Douglas via my jaw's unsuccessful confrontation with planet earth.

I have bruising along the left side of my jaw but the rest of my head is fine. My bike helmet had some very minor damage (an embedded pebble and the part of the foam where the front chin strap triangle attached on the left side is broken - I know I have to throw it out -single crash use and all that). I have bruises and scrapes all over my left side from the top of my shoulder down my left arm and bruising on the left side and my left leg and a very sore only partially functional right forearm (I think it landed under me)

I had no headache at all though that may have been masked by how much the rest of me hurt. No signs of concussion detected by either the EMT or the Emergency Room Doctors. Nothing on a CAT scan.

Yet I was knocked out cold and insensible/incomprehensible for a good 10-20 minutes and have some retrograde amnesia for what happened shortly before and during the accident. I also only have some very spotty recall of the time I was lying on the path incapacitated or how i got onto the stretcher. My wife reports that I was just moaning loudly until I regained some semblance of composure.

So how does one get knocked unconscious with memory disruption and incoherence and then feel perfectly mentally fine after a very brief period of recovery? Other than the shock (and worries about possible brain injury) I probably would have been able to walk away from that accident without the slightest weave.

posted by srboisvert to Health & Fitness (9 answers total)

You hit the ground with your face hard enough and in such a way that your brain smacked against your skull. This isn't good but it's not especially uncommon, especially when you take a hard clock to the jaw. (Think about how a boxer stands in protective stance. There's a reason they keep their head down and jaw covered, it's because getting hit in the jaw is a really great way to get your brain to jostle just right to smack your skull.)

Why this causes you to go unconscious and the exact extent to which you're out is more complicated and involves a lot of different parts of the brain that science doesn't 100% understand, but it's just what the body tends to do in response to a sudden brain impact like that. Maybe it's your body's way to get you to stop doing the thing that caused your brain to get hurt. So the answer to your last question, how do you get knocked unconscious and then feel perfectly fine afterward, is no one really knows, brains are hard, but you got lucky.

p.s. Don't make a habit of knocking yourself unconscious. Science has figured out that that's real bad.
posted by phunniemee at 11:15 AM on July 12, 2016

Best answer: You had a concussion but you recovered quickly and well. A concussion is a "bruise to your brain" and it doesn't show up on CT scan and is only diagnosed clinically based on history and physical exam.
posted by treehorn+bunny at 12:09 PM on July 12, 2016 [7 favorites]

One thing concussion experts are increasingly discussing is the fact that a lack of aftereffects from a concussion (or a subconcussive event) doesn't mean the concussion didn't happen. It just means our diagnostic tools are only flagging the worst ones.
posted by a fiendish thingy at 12:10 PM on July 12, 2016

Best answer: I realized the link I used is technical and aimed at specialists. Here is a layperson's page that you might find more readable. Even if you recover quickly and don't have long lasting effects, what you describe happening after the impact defines the concussion.
posted by treehorn+bunny at 12:12 PM on July 12, 2016 [1 favorite]

When your brain hits your skull like that, it also bounces and hits the opposite side (in this case the back) of your skull. The two hits are respectively known as the "coup" and "contracoup." (You're probably familiar with "coup d'etat," but coup in general is a French word meaning "flash" or "clap" or anything else that occurs in an instant.) Thus, for people who have after-effects, it can be a result of either hit.

General rule: you have a concussion because you were knocked unconscious. (That's a rule of thumb for first-aid, not a medical diagnosis.) Monitor the patient, awake, for 24 hours, watching for cognitive or sensory problems that could indicate bleeding in the head (which puts pressure on the brain). You can do this for someone who had their accident while alone as a precaution, because as you are aware, a person can forget they were unconscious.

If the above is bad advice, I will gratefully accept corrections.
posted by Sunburnt at 12:38 PM on July 12, 2016

Sunburnt, that's good general advice, but it's not necessary to keep a person with a mild traumatic brain injury awake for 24 hours for monitoring. More typical advice would be just to have them be with a responsible adult who would notice if they had any changes in mental status. If concerned may awaken them during the night to check on them, being cognizant that most people aren't normally at their most alert and oriented when they get woken up in the middle of the night.
posted by treehorn+bunny at 12:49 PM on July 12, 2016 [2 favorites]

A severe blow to the jaw twists your brain stem, knocking out your reticular activating system (RAS). The RAS controls consciousness and wakefulness. It's like rebooting a computer - you hit the manual power on/off switch in your brain, then had to wait for everything to start back up. No permanent damage was done (or it's so minute as to not be discernible).
posted by pecanpies at 12:49 PM on July 12, 2016

It's also the source of the "glass jaw" or "power button" in boxing.
posted by rhizome at 5:46 PM on July 12, 2016

Warning! You might not be "fine." Last fall I hit my head and was fine for a few days... and then I suddenly wasn't fine, and have had post-concussion syndrome since then. Concussions don't necessarily come on immediately. So take it easy, still.
posted by The corpse in the library at 6:48 AM on July 13, 2016 [1 favorite]