Sleep and the Brain Flashcards
Why is sleep important?
Sleep is a highly conserved behaviour that occurs in animals and humans. This prevalence not withstanding, why we sleep is not well understood. From a perspective of energy conservation, one function of sleep is to replenish brain glycogen levels, which fall during the waking hours. Furthermore, body temperature has a 24-hour cycle, reaching a minimum at night and thus reducing heat loss. As might be expected, human metabolism measured by oxygen consumption decreases during sleep.
Sleep Stages
There are two basic types of sleep: rapid eye movement (REM) sleep and non-REM sleep (which has three different stages). Each is linked to specific brain waves and neuronal activity. You cycle through all stages of non-REM and REM sleep several times during a typical night, with increasingly longer, deeper REM periods occurring toward morning.
What occurs in the first stage of sleep?
Stage One:
Non-REM sleep is the changeover from wakefulness to sleep. During this short period (lasting several minutes) of relatively light sleep, your heartbeat, breathing, and eye movements slow, and your muscles relax with occasional twitches. Your brain waves begin to slow from their daytime wakefulness patterns.
What occurs in the second stage of sleep?
Stage Two:
Non-REM sleep is a period of light sleep before you enter deeper sleep. Your heartbeat and breathing slow, and muscles relax even further. Your body temperature drops and eye movements stop. Brain wave activity slows but is marked by brief bursts of electrical activity. You spend more of your repeated sleep cycles in stage 2 sleep than in other sleep stages.
What is the Role of Melatonin in Sleep?
Melatonin, the hormone produced by the pineal gland at night, serves as a time cue to the biological clock and promotes sleep anticipation in the brain default mode network (DMN); these effects may explain the increase in sleep propensity in circadian rhythm sleep disorders.
Melatonin levels in the blood stay elevated for about 12 hours – all through the night – before the light of a new day when they fall back to low daytime levels by about 9 am.
