The Science Behind Sleep

Sleep is a natural condition of the body and mind, which typically recurs for several hours every night in which the nervous system is inactive, eyes closed, postural muscles relaxed and consciousness practically suspended. It is an essential part of life and deprivation can lead to threatening consequences but why is sleep so important?

Around a third of our lives are spent sleeping and this is what occurs during that time. Sleep is divided into two main stages non rapid eye movement (NREM) and rapid eye movement (REM).

NREM is made up of 3 stages:
Stage 1 is the stage between wakefulness and sleep and can last 5 - 10 minutes. Muscles are still quite active and the eyes roll slowly and may open and close. During stage one there is a transition from unsynchronised beta and gamma rays to more synchronised and slower alpha rays then to theta waves. The point in which you actually fall asleep is hard to pinpoint due to brain activity gradually slowing down.

Stage 2 is when conscious awareness of the outside world begins to fade and the brain is unable to understand the content of any sounds heard. Brain waves during this stage are mainly theta waves. Furthermore, there are two distinguishing events sleep spindles and k-complexes. Sleep spindles are the short bursts of brain activity lasting approximately half a second each and k-complexes are short negative high voltage peaks followed by a slower positive peak then a final negative peak. Both events work together to protect sleep and suppress outside stimuli. Stage 2 is the stage we spend most of out time in with approximately 50% of sleep being stage 2 & lasts 10-20 minutes each time.

Stage 3 is the slow wave sleep. During this stage you are essentially cut off from the outside work and unaware of any sounds or other stimuli. Brain temperature, breathing rate, heart rate and blood pressure are all at their lowest levelsThis is the stage in which night terrors, sleep walking, sleep talking and bed wetting is most common as well as information processing and memory consolidation. If awakened at this stage they will often feel very groggy and may take up to 30 minutes before they attain normal mental performance. Stage 3 can last up to an hour.

The REM stage of sleep occurs after NREM usually around 90 - 120 minutes into sleep and becomes greater as the night progresses and account for 20-25% of total sleep. During this stage the brain is very active and near the same levels as someone awake. The purpose of REM stage of sleep is still unknown however many scientists link it to having something to do with memory processing, brain development and learning.

Rapid movement of the eyes can be seen and this movement corresponds to what’s occurring in our dreams. The eyes move independently some even looking in different directions. This rapid eye movement indicates lots of brain activity but the brain is completely paralysed during the REM stage. However some people can have a condition called REM sleep behaviour disorder in which the body doesn’t become paralysed. This causes them to act out their dreams and it is common for these people to hurt themselves or mistaking family members as attackers. On the other hand for some sleep paralysis can last a little too long and our bodies can be become paralysed before we fall asleep or continue into a few minutes after we woken up. This experience can be scary especially if unaware of what is happening.

It may look as though we are fast asleep however the body is quite active and theses changes occur:
  • Heat rate increases
  • Blood flow to the brain increases
  • Metabolism increases
  • Blood Pressure rises

Scientists are unable to full agree on the purpose of REM sleep however these are the two main theories:
  • Brain development - babies spend most of their time in REM sleep and it is believed that foetus’ spend all their time in this stage as this is the only source if mental stimulation which is critical for brain development 
  • Help us in learning new skills - the brain becomes very active is the part of the brain responsible for memory. There’s may be links between how much time we spend in REM sleep and how fast we learn something new.

Cycles of NREM and REM last for around 90 minutes before repeating themselves.

Thank you for reading
Amanda Kadye 



Comments

Post a Comment

Popular posts from this blog

PTSD - A Psychodynamic Explanation

Post-traumatic stress disorder (PTSD) is a type of anxiety disorder which you may develop after being involved in, or witnessing, traumatic events. The condition was first recognised in war veterans and has been known by a variety of names, such as 'shell shock'. PTSD can develop immediately after someone experiences a disturbing event, or it can occur weeks, months or even years later. Its estimated to affect about 1 in every 3 people who have a traumatic experience, but it's not clear exactly why some people develop the condition and others do not. There are many theories that could be used to explain this condition. Psychodynamic approaches to PTSD focus on a number of different factors that may influence or cause PTSD symptoms, such as early childhood experiences, current relationships and the things people do to protect themselves from upsetting thoughts and feelings that are the result of experiencing a traumatic event. The psychodynamic approach focuses mainly
Read more

Disparities in Global Eye Care

Vision is one of our most precious possessions. Multiple polls globally show that most people are more fearful of becoming blind than losing any other sense. (1,2) With sight being such a valuable asset, one would assume that eyecare is at the forefront of medical services across the world. Living in the developed world, we perhaps take for granted the simple and yet crucial services available to us such as regular eye tests, glasses, contact lenses and high-quality ophthalmic care - most of which can be accessed for free or at a subsidised price. However, in many parts of the world this is not the case. 285 million people worldwide are visually impaired, with 90% being from developing countries. (3) In China, for example, levels of blindness are increasing each year, however critically, rates of blindness have been reported at up to 4 times higher in the developing world as compared to more economically developed countries (4, 5). This is particularly worrying given that around 80% of
Read more

Do Contact Lenses Really “Support Your Vision”?

Image
Contact lenses have been frequently used as an alternative to glasses. Compared to the heavy-framed glasses in front of one’s eyes (optic glasses), thin plastic discs on the eye (contact lenses) help correct refractive errors in both myopic and hypermetropic users. The lens’ shape and power can be tailored to the user’s sight. A concave lens can be used to decrease myopia by reducing light refraction and increasing focal length so that the image is formed on the retina (1)  (Figure 1). Alternatively, a convex lens can be used to limit hypermetropia in an opposing mechanism to concave lenses (1) (Figure 1). Figure 1, An illustration of myopia and hyperopia and how adding lens of different shapes in front of the eye can be used to alter the refraction of light and correct each impairment in vision (10) Besides supporting sight, which both types of lenses can do, contact lenses confer some advantages that make them preferable to glasses. Unlike glasses, contact lenses are less likely to f
Read more