Video narration
Why can your hand pull away from something hot before you have time to think? Touch a hot surface, and sensors in your skin detect danger. They send a signal toward your spinal cord, carrying the warning from your hand. There, the message enters a fast route: a movement signal travels back to muscles in your arm, and they pull your hand away. That first movement doesn't wait for your brain to make a conscious decision. Your brain is still informed about what happened; the spinal route simply gets the protective action started quickly. The path from detecting danger to moving away is called a reflex arc-the route that links the warning to the muscle response. So why does your hand move before you decide? In a classic withdrawal reflex, your spinal cord triggers the movement quickly, while your brain registers what happened.