The correct statement about the optic nerve is:
It senses bright light and tells your brain.
The afternoon bell rings, and students hurry out of the classroom. They step outside into the bright sunshine. Some of them smile up at the blue sky. Others reach for their sunglasses to shade their eyes. But a few do something else. Like what?
A…a…achoo!
That's right—some people sneeze whenever they suddenly step into bright light. Scientists call it photic sneeze reflex (PSR). (Photic means "having to do with light.") Many people call it sun sneezing. Scientists think that between 10 and 35 percent of people have PSR.
Scientists have been studying sun sneezing for a very long time. But even today, experts aren't exactly sure what causes PSR. But it might be mixed-up brain signals.
Two nerves in the head are close together. One is called the trigeminal nerve. It sends signals from the nose to the brain. Here's how it works: Say dust gets in your nose. The trigeminal nerve senses the dust and sends a message to your brain. Then, you sneeze to get rid of the stuff.
The optic nerve is nearby. It sends signals from the eyes to the brain. The optic nerve senses bright light, and then it tells your brain that something's up. Usually, your pupils get smaller.
But, for photic sneezers, something different happens. Scientists think that the two signals cross. The trigeminal nerve gets the signal from its neighbor—the optic nerve. So, you sneeze! No dust needed.
Scientists have another name for sun sneezing. They call it ACHOO!
Question 1
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Think about the article. Which is true about the optic nerve?
It gets signals from the brain.
It is far from the trigeminal nerve.
It senses bright light and tells your brain.
It senses dust in the nose and tells your brain.
1 answer