My answer to What happens neurologically in the brain when you can’t fall/stay asleep. How does sport/being active …

Answer by Connie b. Dellobuono:

Just as antibody production is connected to both exercise and happiness, so too is endorphin production.

20-min walk triggers endorphins in the brain. Endorphins are chemicals that are able to cross through the gaps between neurons in order to pass along a message from one to the next.

Serotonin plays a definite role in sleep cycles, as high levels of serotonin are associated with wakefulness and lower levels with sleep. Serotonin also is synthesized by the pineal gland to make melatonin, the hormone that is directly related to healthy sleep.

Adenosine antagonist, caffeine, is the world-wide most popular wakefulness inducing and maintaining substance. Caffeine reduces slow-wave activity in the subsequent sleep episode and caffeine consumption during prolonged wakefulness counteracts the typical effects of sleep deprivation…