You see stars when you get up too fast?

Answer 1

AnswerWhen you bump your head you cause damage to various cells that make up your tissues. Consequently, the cells release prostoglandins, and other molecules including vasodilators and constrictors, that activate an immune response. Specifically they modulate a non-specific inflammatory response, which in a nutshell causes increased blood flow to the damaged area (simplified version). The whole purpose of the increased blood flow is to allow the transport of critical immune molecules (neutrophils, monocytes, lymphocytes) to the site of damage so that they may begin the repair process.

Answer 2

Whilst you don't see literal "stars" (ie big yellow stars, Tom and Jerry style) you can get a "twinkling effect". I usually get this a couple of times a game on the Rugby pitch!

Seeing stars is usually due to a lack of blood reaching the brain, and thus a lack of oxygen. Most commonly this happens after standing up quickly or straightening after bending over. You don't see it all the time because the arteries serving the brain reflexively dilate to maintain pressure, but those reflexes may be disturbed by lack of sleep or food, a hangover, or an infection. Physical trauma may also cause the reflex to malfunction, which is why stars float around Sylvester the Cat's head when he gets bonked. Rarely, seeing stars can be caused by too much blood reaching the brain.

The stars you see are actually neurons in your visual cortex misfiring, a hallucination at the lowest possible level. When the neurons' oxygenation changes drastically, their membrane potential also changes. Ordinarily this wouldn't matter, because all of the surrounding neurons' potentials would change at the same time. When it happens due to standing quickly or taking a few G's of acceleration, the change happens so fast that the neurons closest to capillaries change well before the surrounding neurons. This causes them to fire spontaneously which your brain interprets as vision; you see stars.

Answer 3

I have heard this a lot, and always wondered myself, I can remember as a kid pressing on my eyes to rub them and seeing stars.

The retina of your eye will respond to either light or pressure, the pressure causes the cells to fire same as light would giving you the impression that sparks are going off inside your eyelids.

For an example close your eye and place your fingertip on your closed eyelid, now move your finger around gently, you will see an aura of light around our finger.

This is not actual light, but the forced firing of the photo reactive cells in the retina making your brain think light is being seen, it is the way your brain is meant to interpret signals from the eye.

Also when you cough or sneeze you can cause enough pressure to fire these cells as well.

Another cause for seeing stars is like in the Cartoons when you see a circle of stars going around the characters head. This is a real thing, when you hit your head hard enough a shock wave transmits across your head to the eye and a pressure firing of the retina cells happens, combine that with the dizziness you often feel with a bad hit on the head and yo can imagine why cartoonists portray it that way.

Answer 4

This is caused by neurons in your visual cortex misfiring.

It happens do to a lack of blood to the head and thus a lack of oxygen. This can happen when you stand up too quickly, suffer head trauma, strenuous exercise or sometimes with migraine headaches.

Answer 5

It mean's you have a low blood pressure.

I'm currently having that problem at the moment.