I grew up fascinated by the clockwork mechanical systems of our industrial world and studied systems engineering at university, but hated the seemingly meaningless, messy complexity of biology. It was only much later that I came to understand how biology was actually much more sophisticated and avoided the fragility of mechanical systems, instead often making use of the optionality and resilience of chemical processes.
You just need to compare a simple mechanical metronome with the complex interactions between Melatonin and Adenosine and other chemicals for controlling the sleep-wake cycles in most biological entities (humans included).
In a fascinating book called “Why We Sleep” by Mathew Walker I recently learned that the Pineal Gland in our brains produces Melatonin on a sinusoidal 24+ hour cycle and it is subsequently eliminated from our bodies by our Livers. Melatonin production is regulated by the Suprachiasmatic Nucleus in our brains that, among other things, detects daylight through our Optical Cortex. Melatonin production is like a 24-hour metronome, but the Suprachiasmatic Nucleus adjusts the time base depending on external conditions which explains why our metabolisms can adjust to timezone changes. Melatonin levels in our bodies help control many time regulated bodily processes, including wakefulness.
Our central nervous system also produces Adenosine while we are awake and its buildup creates a “sleep pressure” that controls many bodily processes that make us sleepy. Adenosine is also continuously metabolized (decomposed) in the body. Thus Adenosine levels in our body rise when we are awake and fall when we sleep.
In the mornings, after sleep, Adenosine levels in our bodies are low and Melatonin levels fall making us wide awake and active. Later, in the evening, Adenosine and Melatonin levels have risen causing us to get sleepy. Various chemicals, notably caffeine, can interrupt this cycle by interfering with the effects of Adenosine on the body, thus delaying the onset of sleepiness.
Researchers know we experience two kinds of sleep – REM and NREM – and we cycle between them several times each night, and that the cycling changes as we grow up and age. REM is an acronym for Rapid Eye Movement and it is associated with dreaming; NREM is Not REM, and no dreaming there!
I find it fascinating that nearly all life on Earth sleeps. Even microbes and bacteria display periodic dormancy and most animals show evidence of REM and NREM sleep. Given how vulnerable to predation animals are during sleep, it must perform an essential life function. Even fish and migrating birds are known to put different parts of their brains into “sleep mode” at different times each day.
We now know that NREM and REM sleep are crucial for consolidating our memories, integrating them into our life view/experience and building associations between different life experiences, which are essential for creativity and innovation. NREM sleep seems to transfer our daily experiences to long term memory and to build on existing associations. REM sleep then seems to trim unneeded memories and build new associations. As well as this mental housekeeping, a lot a physical housekeeping also occurs while we sleep to regulate, repair and replenish our bodies.
I will go into some of the fascinating reasons for and functions of sleep in future articles, highlighting their relevance in Macau.