UMEM Educational Pearls

Title: Basics of Sleep Physiology and Architecture

By: Youssef Annous, MD

Sleep is integral for physical and mental health and performance. Sleep is extremely well conserved among species. All mammals need sleep to survive.1 A single sleep cycle typically lasts anywhere between 90 and 120 minutes and is broken down into two phases2:

Non-Rapid Eye Movement sleep

Stage 1 (Light Sleep)

This is the lightest form of sleep and the easiest to wake up from. During this stage, it is normal to experience muscle twitching and the sensation of drifting in and out of consciousness. This stage lasts approximately 5 minutes in the beginning of sleep and comprises around 5% of total sleep duration.2

Stage 2 (Light Sleep)

During this stage, you are likely to begin experiencing decrease in body temperature, heart rate (HR), blood pressure (BP) and respiratory rate (RR). Electroencephalography (EEG) during this phase of sleep would show sleep spindles and K complexes.2 These findings have been linked to memory consolidation.3

Stage 3 (Deep Sleep)

This is the deepest stage of sleep. During this phase, body temperature, HR, BP, and RR are at their lowest. This is the most restorative stage of sleep. It is essential for immune health, cardiovascular health, tissue repair, bone growth, and muscle recovery.2 It is also when growth hormone (GH) is at its highest. Physiological (e.g. illness) or psychological (e.g. anxiety) stressors can negatively impact this stage. We experience less deep sleep as we age.4

Rapid Eye Movement (REM) sleep

This stage of sleep is characterized by rapid eye movement, abundance of dreaming and heightened brain activity. During REM, there is total body paralysis with exception of ocular and respiratory muscles. It is theorized that your body is paralyzed during this stage to protect you from dream enactment. You experience more REM the longer you sleep. REM has been shown to be essential for memory consolidation, cognitive function, mood regulation and for coping with stress. This stage is particularly compromised by sedatives including but not limited to alcohol, benzodiazepines, and tetrahydro-cannabinoid (THC). Several studies in animals and humans showed that even modest REM sleep deprivation can result in increased mortality. 2,5,6

All sleep stages are extremely essential. Be careful of self-medicating with sleep aids such benzodiazepines or alcohol as this can be detrimental for your health. In later UMEM pearls, we will discuss protocols, supplements and behavioral ways to improve each stage of sleep for better mental and physical health.

References

References:

1 Miyazaki S, Liu C-Y, Hayashi Y. Sleep in vertebrate and invertebrate animals, and insights into the function and evolution of sleep. Neuroscience Research. 2017;118:3-12. doi:10.1016/j.neures.2017.04.017

2 JF; PAVK. Physiology, sleep stages. National Center for Biotechnology Information. Accessed May 26, 2024. https://pubmed.ncbi.nlm.nih.gov/30252388/.

3 Antony JW, Schönauer M, Staresina BP, Cairney SA. Sleep spindles and memory reprocessing. Trends in Neurosciences. 2019;42(1):1-3. doi:10.1016/j.tins.2018.09.012

4 El Shakankiry H. Sleep physiology and sleep disorders in childhood. Nature and Science of Sleep. Published online September 2011:101. doi:10.2147/nss.s22839

5 Della Monica C, Johnsen S, Atzori G, Groeger JA, Dijk D-J. Rapid eye movement sleep, sleep continuity and slow wave sleep as predictors of cognition, mood, and subjective sleep quality in healthy men and women, aged 20–84 years. Frontiers in Psychiatry. 2018;9. doi:10.3389/fpsyt.2018.00255

6 Leary EB, Watson KT, Ancoli-Israel S, et al. Association of Rapid Eye Movement Sleep with mortality in middle-aged and older adults. JAMA Neurology. 2020;77(10):1241. doi:10.1001/jamaneurol.2020.2108