Memory, sleep and nervous-system hygiene

Sleep is a natural state of reduced response to external stimuli, during which nerve cells recover from fatigue. Sleep consists of cycles repeated 4–5 times: in slow-wave sleep breathing and heartbeat slow and muscles relax, while in REM sleep eye movement increases, breathing quickens and most dreaming occurs. During sleep the brain organises learned information, growth hormone is released and immunity is strengthened. Sleep centres lie in the brain stem and diencephalon; the cortex is inhibited, while vital centres in the medulla (breathing, heart) keep working. The amount of sleep varies with age: a newborn sleeps much, a school-age child needs about 9–11 hours and teenagers about 8–10 hours (depending on the person). Healthy sleep habits: go to bed and wake at the same times, switch off screens (phone, TV, tablet) an hour before bed, avoid heavy food and caffeinated drinks in the evening, make the room aired, dark and quiet, be active in the daytime. If sleep is constantly disturbed or you feel very sleepy in the day, tell adults and see a doctor; do not take medicines or “sleeping pills” yourself.