We all know we can’t function without sleep. And that’s exactly the reason why this incredibly integral part of our life has mystified us for thousands of years, with answers to pertinent questions like what happens to our mind and body when we sleep, having been left unanswered. But the mystery is unfolding and we have finally understood the physiology of sleep to a great extent, though not fully.
The sleep cycle
Your sleep cycle is made of REMs (Rapid eye movement) and NREMs (Non-rapid eye movement) and this cycle repeats itself every 90 minutes, according to National Sleep Foundation. While NREM is the deeper part of the sleep, REM is the more active part. When you start to fall asleep, the sleep architecture starts with NREM, which is also said to constitute 75 per cent of the night. It is also the time when you are in deep sleep. So what exactly happens in these two cycles?
NREM occurs in the below three stages:
NREM (Stage 1)
Light sleep / Easily awakened
Disengaging from your surroundings
Regular breathing and heart rate
Drop in body temperature
NREM (Stage 2)
Enter deepest and restorative sleep
Drop in blood pressure
Eye movement stops
Increase in blood supply to muscles
Tissue growth and repair
NREM (Stage 3)
Restoration of energy
Important hormones are released
Slower brain waves
REM occurs after NREM. As the night proceeds, duration of REM gets longer. This is what happens when you are in the REM cycle of the night:
Providing energy to brain as well as the body
Brain gets active/ Dreaming
Muscles are turned off
What happens in sleep?
Sleep is the time when our brain resets. Explains Dr Suresh Kumar, HOD, Department of Neurology, Amrita Institute of Medical Sciences, Kochi, “When you sleep, your brain rests. When the brain rests, your heart rate comes down. Moreover, your memory gets reinforced during sleep.” So if you don’t sleep well, your brain isn’t rested and it makes it difficult for you to concentrate or even stay awake at daytime. It also impacts your memory, in turn affecting every aspect of your waking up hours.
New data suggests that NREM part of the sleep cycle is the restorative and relaxing part of the sleep. On the other hand, REM is the cycle where eyes are rapidly darting back and forth and brain waves are almost similar to your waking hours. This is the time when your brain is active almost like your waking hours and muscles are almost paralysed. It is more important for learning and memory tasks. Several literatures explain that REM is the part of the sleep that helps consolidate your emotions. This is the cycle where your muscles shut but your brain is in full activity. Since this is the part of the sleep cycle when you dream, it turns off motor neurons in your spinal cord, leading to temporary paralysis, preventing you from acting upon your dreams.
Dr Vivek Anand Padegal, Pulmonologist, Fortis Bangalore further explains, “While both REMs and DREMs are extremely important to complete your sleep cycle, if you have a sleep disorder, it impacts your REM greatly.”
Our sleep pattern is administered by a biological clock present in the brain. It increases production of melatonin hormone by evening and switches it off on sensing light. This hormone helps you fall asleep naturally. Dr Kumar elaborates, “Melatonin is important to maintain a sleep-wake cycle. However, if you are working odd hours and not sleeping on time, it confuses the sleep-wake cycle, leading to disrupted sleep.”
Talking about the side effects of disrupted melatonin production, Dr. Salil Bendre, Head, Pulmonary Medicine at Nanavati Super Speciality Hospital, Mumbai, says, “Normal sleep ensures normal hormones. Melatonin levels get altered if the sleep gets disturbed. This leads to depression and irritability. Improper and disturbed sleep also causes certain hormones to be produced which may cause weight gain.” Sleeping is believed to regulate hormones that determine our feelings of fullness and hunger. So if you are sleep deprived, your body may stop sending these important signals to your brain, leading to weight gain.
A bad sleep or a sleep disorder?