Not Always This Way

Ok, maybe your grandparents probably slept like you.  And  your great, great grandparents.  But once you go back before the 1800’s, sleep starts look a lot different.  Your ancestors slept in a way that modern sleeps would find bazaar— they slept twice.  And so can you.

We didn’t always sleep in one 8 hour chunk.  We used to sleep in two shorter periods, over a longer range of night.  This ranges about 12 hours long, and began with a sleep of 3-4 hours, wakefulness of 2-3 hours, then sleep again until morning.

We are Tired

Oxygen, water, food, sleep.  These are four requirements for life.  Without them (in varying lengths of times) people die.  Sleep is an important factor as it heavily influences our performance at work, our risk of chronic disease, and our overall quality of life.  Sleep researchers, however, aren’t clear on the exact reason why humans even need to sleep.  From an evolutionary perspective sleep would certainly have left primitive humans vulnerable to attack.  So it must offer some great advantage.  Generally speaking, sleep is thought to allow our brains and our bodies to heal and repair from the damage of the day;  synaptic plasticity is managed, brain pathways that are not being used are pruned, muscles repaired, and energy stores are replenished.

Sleep is an active process.  You don’t fall asleep because your brain is tired.  Sleep activity is maintained throughout the night.

Short sleep is defined as less than 7 hours.  In the US, 24-48% report sleeping less than 7 hours.

Humans have a 24-hour circadian rhythm.  This is maintained even in the absence of environmental clues.  However, external clues can influence this.

Other animals have a reverse pattern – mice and rodents.

Stages of Sleep

Non-REM – 4 substages.  Neuronal activity is low, metabolic rate and brain temperature are at their lowest, heart rate decreases, blood pressure lowers, and muscle tone and reflexes are intact.

REM – (Rapid Eye Movement).  Brain activity is similar to waking state.  Brain temperature and metabolic rate rise, and complete loss of muscle tone with the exception of the diaphragm (so you can breathe), eye muscles, and some muscles of the inner ear.