From a medical point of view, sleep can be understood as a state of mind experiencing reduced levels of consciousness involving a temporary inactivity of nearly all voluntary muscles, and a relative suspension of sensory and non-motor activity. In simple terms, sleep is an impermanent physical and mental state of the mind during which most of the external stimuli are blocked from the senses, and the individual stops responding to the environment. There are different types of "sleeps" depending upon the intensity and manifestation of sleeping criteria. The ability of the person to "awake", or come out from the transitory partial inactive state of the mind depends upon several factors, and these factors vary from person-to-person. Even though it can't be proved on a conclusive basis, medical experts believe the basic purpose of sleep is to create a state of inertness in the human body, during which the body can repair itself and regulate the metabolism to improve its functioning, and the state of inertness helps save the energy which is utilized for the rejuvenation process.
Repair theory As per this theory, during the "awake" period, the body is physically and mentally responding to the various activities associated with our daily activities and this consumes large amounts of energy. The energy utilized is depleted from the energy reserves stored in various parts of the body. The replenishment and body repair activities can occur effectively when the body is undergoing a state of rest - when no extra energy is utilized for any physical processes or activities. The sleep period ensures all the resources in the body are utilized in an optimum manner for the maintenance and up-keep of the various metabolic processes occurring in our body that keep us alive.
Adaptive theory According to this theory, sleep is a naturally evolved phenomenon that humans and animals adapted to for their survival. Sleeping helps in preserving energy, and prevents exposure to dangers and predators.
How "sleep" works? As far as the process of sleeping is concerned, scientists believe that our metabolism has two processes: • The sleep-awake process • Circadian biological clock or Circadian rhythm which regulate our sleep. Both the processes function in tandem, and create the "sleep cycle" because of which we tend to feel sleepy at night, and remain awake during the day. The processes regulate our sleep cycle, which scientists believe is essential for body repair and sustenance. The Circadian biological clock can be understood as a 24-hour condition during which the body rhythm is affected by sun light. The presence and absence of sunlight controls the secretion of certain essential hormones in the body. The melatonin hormone (N-acetyl-5-methoxytryptamine) is secreted in the absence of sunlight, generally at night, and is primarily responsible for regulating the body temperature. The cycle needs to be in accord with the physical state of the individual and the metabolic functioning of the body.
Circadian rhythm or the "sleep cycle" A Circadian rhythm is an approximately 24-hour cycle associated with the biochemical, physiological, and/or behavioral processes. The term "circadian" is derived from the Latin word "circa" which means "around", and "diem" or "dies" which means "day". Therefore, the term literally means "approximately one day". The rhythm is generated by a metabolic activity which functions as an internal body clock, and which is synchronized with the "light-dark" cycles as well as the changes taking place in the subject's environment.
Stages of sleep The sleep process consists of two main stages which keep on repeating in a cycle of 90 to 110 minutes during the entire sleeping activity. The two stages are: • REM (Rapid Eye Movement) • Non-REM (Non - Rapid Eye Movement, which is further classified into four sub stages)
REM and Non-REM sleep There is a subtle difference between the dreams occurring during the REM and Non-REM stages of sleep. Dreams occurring during the Non-REM stage are brief and fragmentary, do not have any lasting impression on the individual, and they are easily forgotten. In this particular stage, the individual is less likely to experience any lucid and clear visual images resulting out of the dreaming process. During the REM dream stage, a portion of the brain called "pons" shuts off all chemical signals associated with voluntary muscles functioning to the spinal cord. This causes temporary paralysis, and the body becomes incapable of any voluntary movements. The REM sleep signal originates from the pons. This is a natural defense mechanism which prevents the person from harming himself or herself during sleep, since the dreams occurring during the REM stage of sleep can seem to be real and life-like, and this can cause the subject to respond physically in accordance to the particular dream pattern. It is believed pons secretes acetylcholine, a chemical compound that acts as a neurotransmitter, during the REM stage which is transmitted to different parts of the forebrain. This causes cholinergic activation within the affected tissue areas. This is what causes the "dream" phenomenon.
Dreams From a scientific point of view, there is no fixed definition of "dreaming". A dream can be interpreted as a succession of images, sounds, and emotions that the human mind experiences during the sleeping process. The basic Les bases du sommeil purpose and manifestation of the dreaming phenomenon is still not clearly understood, and scientists have several hypotheses which try to explain the process. However, it is commonly believed amongst scientists that dreams are basically a result of certain psychological or neuropsychological activities occurring in certain portion of the brain. Dreams are associated with the psychological aspect of the brain - the non-tangible part (mind), and not the tangible part (brain). It's important to differentiate between the two. During the lifetime, it is believed a human being spends approximately six years dreaming, which comes to around two hours on a daily basis as an average, if we are to consider the average life span of a person. It is still unknown exactly how and why dreams originate, and whether there is a single origin, or multiple portions of the brain are involved.
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