how do we sleep even if their is a lot of noise where your sleeping? why???

Question: how do we sleep even if their is a lot of noise where your sleeping? why???
- Keywords:
  health,
  sense,
  sleep
Asked by areehaj to Kate on 11 Mar 2014.
- Kate Salmon answered on 11 Mar 2014:
  
  Hi @areehaj, some people can’t sleep with a lot of noise but other people can. I personally can’t sleep with much noise but some people who live in cities near to big roads or train stations get used to the noise over time and their brain can ‘cancel it out’ as background noise. Our brain is particularly good at this. For instance when someone is speaking to you in a noisy classroom, you can still hear them if you concentrate on their voice because your brain has cancelled out the classroom noise as ‘background noise’. Older people who have hearing aids sometimes have trouble hearing in noisy places because the hearing aid makes everything louder rather than just the things you want to hear louder.

Question: how do we sleep even if their is a lot of noise where your sleeping? why???