The ear continues to work while you sleep, which is why loud noises wake you.

The longer version

Auditory processing continues through sleep because the pathway from the ear to the brain remains active. Sound waves still move the eardrum and the tiny bones behind it, hair cells still convert that motion into nerve signals, and those signals still reach the brain stem and the auditory cortex.

What changes is how the brain responds: during sleep it filters incoming information against the background of the body's own state, and only signals that stand out, such as a loud or unexpected noise, trigger a full awakening. Familiar or steady sounds are often absorbed into sleep instead, which is why some people wake at a sudden bang but not at traffic.

Where this entry sits

These facts look at how the human body works in ordinary moments, from breathing and blinking to balance and sleep. They focus on anatomy, senses, and small reactions that happen constantly without any conscious effort. The full list sits on the Human Body page, where every entry is listed in order.