In the Dark: The Science of What Happens at Night

In the Dark: The Science of What Happens at Night — page 5
Tick Tock OUR BIOLOGICAL CLOCK You probably wear a watch or carry a device that tells time Like other living creatures you also have a biological or built in clock that helps determine when you should be awake and when you should be asleep This natural programming of your body is known as a circadian sir CAY dee an rhythm In the same way that Earth rotates on its axis once every 24 hours your body follows a 24 hour cycle of waking and sleeping Your brain contains a group of nerve cells called the suprachiasmatic nucleus soo prah KY as MAT IC NOO clee us or SCN located between and behind your eyes The SCN picks up clues about light and dark from the retina a thin layer of tissue at the back of your eye that receives light and sends electrical signals to your brain The SCN sends messages to other parts of your brain and body to coordinate the timing of important tasks such as eating sleeping and producing hormones When it grows dark outside the SCN tells your body to release melatonin a hormone that helps you feel drowsy The melatonin levels in your body are ten times higher at night than they are during the day Suprachiasmatic nucleus Light Retina When the SCN detects daylight reaching your retina it sends messages to let your body know it's go time Your temperature rises and your body releases a hormone called cortisol which makes you alert