Reflex

body science · automatic response · nervous system

Lightning-fast response. A reflex happens so quickly that your brain doesn't have time to make a decision. Your spinal cord sends the signal back to your muscles almost instantly, which is why you pull your hand away from something hot before you even feel the pain.

Automatic and unplanned. Unlike things you do on purpose, like riding a bike or solving a math problem, reflexes happen without you choosing them. Even if you try to stop a reflex, your body does it anyway because it's protecting you.

The knee-jerk test. When a doctor taps your knee with a little hammer, your leg kicks out by itself. This famous reflex shows how your nervous system works without your brain getting involved at all.

Your pupils shrink. When bright light shines in your eyes, your pupils automatically get smaller to protect them. You don't decide to do this, your body just does it to keep the light from damaging your eyes.

Catching reflexively. If someone tosses something at you, you catch it without thinking about it. Your eyes see it coming and your hands react instantly, which is why reflexes are often faster than conscious thought.