Those of us who suffer from chronic pain know how precious and elusive sleep can be. Awakening repeatedly or having trouble getting to, or staying asleep, is a constant issue. In order to function at our best we need to experience all stages of sleep since each one is vital to the nightly ritual that allows us to recover, repair, remove toxins, regulate conversion of food to energy, facilitate memory retention and learning abilities and prepare for a new day.
Humans spend one third of their lives asleep. Its nourishing and rejuvenating properties impact every moment. That’s why it’s so important to understand what happens when we sleep and why each stage is critical to feeling well and staying healthy.
By using an EEG (electroencephalogram) we can view brain wave activity during sleep and the resultant changes in our bodily activities e.g. blood pressure, heart rate, muscle movement, and hormones that are increased, or suppressed, in each phase.
Brain chemicals are responsible for keeping us awake or encouraging us to fall asleep.
Neurons in the brain stem- where the brain meets the spinal cord- produce neurotransmitters such as serotonin, cortisol, dopamine, and norepinephrine, which keep us awake and functioning throughout the day.
Neurons at the base of the brain turn the signals from the brain stem off, causing us to fall asleep. Adenosine is a chemical that makes us feel drowsy. It’s released slowly by late afternoon, then dissipates when we are asleep to allow us to awaken alert and ready for the new day. When darkness comes, the optic nerve signals the pineal gland to release melatonin which also makes us tired and ready for bed. It signals the release of cortisol at first light.
Over the course of a night we generally experience four to six sleep cycles, each composed of four stages lasting 90 to 120 minutes. Too often these cycles are interrupted by pain, illness, or anxiety.
NREM stage 1 is the transition between wakefulness and sleep. It’s the lightest stage of sleep.
The brain, heart and lungs slow down, muscles relax. The brain is still active, producing theta waves- slow waves predominantly from the frontal lobes. This lasts 5-10 minutes.
NREM stage2 comprises 50% of each sleep cycle. We are less aware of our surroundings, core temperature drops, eye movements stop, breathing and heart rate become regular. Rhythmic brain activity produce sleep spindles on an EEG thought to be when we filter, process and consolidate memories. This lasts 20-60 minutes
NREM stage 3 slow deep delta waves emerge. In deep sleep we aren’t aware of outside stimuli. Our muscles are completely relaxed, breathing and blood pressure at their lowest. Tissue repair, growth and cell regeneration occur. Builds bone and muscles. Immune system is strengthened. Here we process and consolidate knowledge and experiences from the previous day. This lasts 20-40 minutes.
REM stage 4 there are two phases of REM sleep- phasing and tonic. Phasic REM sleep has bursts of rapid eye movements. Tonic REM sleep does not. Here our brains are the most active but our bodies are temporarily paralyzed. Breathing becomes quicker and more irregular, eyes move rapidly, and we dream. It’s thought we process emotions here and all the information we deem important is cemented into our memory.
Usually starts 90 minutes after we fall asleep and lasts 10 minutes the first time. It increases with each successive cycle until the final sleep cycle which can last 30-60 minutes. It’s in the last two stages we strengthen immunity, repair and rebuild cells.
We don’t progress from stage 1 to 4 in sequence. In a perfect world with an uninterrupted nights sleep the stages are:
NREM stage1 –>NREM stage 2 –>NREM stage 3 –> Then NREM stage 2 –>Then REM sleep –> A return to NREM stage 2 –>
Then REM stage 3 again. This stage becomes progressively shorter in each cycle and may actually disappear during long periods of rest.
The cycle then rotates from REM2 to REM3 with a brief return to REM2 before entering REM sleep for progressively longer periods of time.
Lack of sleep leads to irritability, fatigue, weight gain, worsening pain, chronic illness, and accidents. It’s not just about the quantity we get each night, the quality is equally important. Fragmented sleep can prevent the much needed restorative stages from happening. Next week I’ll discuss what can be done, or should be avoided, to help us sleep through the night.