Sleep and waking Is a phenomenon that is found in everyday life of both human and animal life Humans spend about a third of their lives sleeping. Shows the importance of sleep to life Sleep plays an important role in the body, for example, affecting the secretion of hormones, alertness, decision-making, memory and other functions of the nervous system. Sleep is a phenomenon that requires systemic functioning of the nervous system that controls sleep and waking. Most humans tend to understand that sleep is the body to rest. As if shutting down the computer When waking up like a computer, ready to go Ready to process in fact Our sleep in daily life Is a process with a step system And the sequence of processes that are quite complex Which needs to be understood more
Sleep stages
Although sleep seems to be physically stagnant or in a constant state But the study found that during the time of sleep can still be divided into various phases. Which has different physiological expressions Methods that are widely used in different stages Of sleep is Polysomnography (PSG), which consists of 3 main types of records:
- Electrocardiogram (electroencephalogram; EEG) to record brain activity
- Electrocardiogram (electro-oculogram; EOG) indicates eye retraction
- Electrocardiogram (electromyogram; EMG) records contraction and muscle tone (muscle tone)
Photo 1 Polysomnography Displays the recording of the terminal at the left eye (E1) and right eye (E2) to record the electro-oculogram. (Two lines on the top) Recordings on the chin for recording electromyogram (EMG) and recording terminal at the scalp (C4, C3) for electroencephalogram recording (Bottom line) The recording terminal on both ears (A1, A2) is used as a reference electrode.
Making it possible to separate the range of sleep into Rapid Eye Movement Sleep (REM Sleep) and Non rapid eye movement sleep (NREM Sleep) is also divided into 4 phases (NREM stage I – IV) according to the depth of sleep By observing the characteristics of the brain wave that is larger and the frequency decreases respectively
Image 2 Polysomogram showing various stages Of sleep and awakening [Ganong, 2013]
NREM stage I periodically begins to fall asleep The brain waves are small. There are many frequencies. Notice the Theta wave, which has a frequency of about 4-7 Hz. Found in the condition that will flow from consciousness To the drowsiness And can be found while that person is doing meditation at a high level This distance can be easily awakened.
NREM stage III and NREM stage IV are deep sleep stages Awake easily The dominant electric wave in this period is the delta wave, which is a large wave with a frequency of approximately 0.5-4 Hz, which is the highest in the NREM stage IV. In some texts are included Both of these periods of sleep are the NREM stage III of sleep.
Throughout the NREM sleep, muscle contraction and muscle tension will decrease accordingly. And there was no rhythmic eye retraction at this stage
REM Sleep is still a period of sleep. This type of sleep Eat about 20-25% of the total sleep time. But the electric wave of the brain is small and the high frequency resembles the beta wave found during waking This term may also be called a paradoxical sleep. At this stage, the eyes will be quickly rhythmically detected. The muscle tone will disappear. Sympathetic activity will increase at this stage. Responding to external stimuli such as loud sounds or internal stimuli such as hypoxia Will be very small compared to NREM stage. In addition, erectile dysfunction also occurs during REM sleep.
Picture 3 Brainwave (EEG) shows the characteristics of the brain wave at various frequency ranges That can be found in normal and abnormal conditions (A) and recorded electrocardiogram at various stages Of sleep Note that while waking, the brain waves are small and high-frequency (beta wave) and the brain waves are larger and the frequency decreases respectively in the NREM stage I-IV.
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Cycle of sleep phase
Each night of normal sleep Will consist of NREM-REM circuits about 3 – 6 cycles continuously. This cycle is called the NREM-REM cycle. This ultradian rhythm, which takes about 90 – 110 minutes
After starting to sleep Normal people take about 15-20 minutes to enter the NREM stage I. The duration from going to sleep to sleep is called sleep latency, which can be changed by many factors. For example, if sleep deprivation makes sleep latency shorter or younger Has a shorter latency than when age increases, and then sleep will continue into the deepest phase of sleep (NREM stage II – IV) and REM sleep, respectively. The first REM sleep will appear about 90 minutes after t The above mentioned NREM – REM cycle is repeated every 90-110 minutes. Each night of sleep will sleep in NREM stage I, II about 50 – 60% and REM sleep for about 20 – 25% of Total sleep time (total sleep time), with the duration of REM sleep increasing respectively in the latter Of sleep Which is opposite the NREM stage III, IV, which can be found in the early stages Of sleep and appear less at the end Duration of sleep And the proportion of sleep during NREM stage III, IV and REM sleep decreases with age
Picture 4 The structure of sleep (left) and total sleep time and the proportion of sleep in various stages compared to age (right) [Ganong, 2010]
NREM and REM sleep mechanism
Sleep in the REM range has a special characteristic that differs from NREM sleep. The most important characteristic is the brain wave that resembles waking. Rapid eye retraction And the disappearance of muscle tone. Caused by different brain functions in the NREM and REM stages, found in sleep, REM, neuronal groups that release neurotransmitters. noradrenaline and serotonin continue to decrease While nerve cells that release neurotransmitters acetylcholine In the brain stem working more This group of neurons sends nerve endings to the thalamus and basal forebrain, causing an electrocardiogram that is characteristic. desynchronized The nerve endings that are sent to the paramedian pontine reticular formation (PPRF), which affect the neuron command of the eyeball Cause eye peeling In addition to this, the cholinergic nerve cells in the brain stem also send nerve endings to stimulate the medullary reticular formation, which plays a role in inhibiting the body’s muscular balance through medulary reticulospinal muscle tone reduction.
Fig. 7: The mechanism of REM sleep: REM on (cholinergic neuron in LDT / PPT). Increased function during REM sleep to stimulate thalamus, causing cortical activation of pontine paramedian reticular formation (PPRF), which controls ocular motor nucleus (OMN). Rhythmic eye retraction And also stimulating ventromedial medullary reticular formation to inhibit α-motoneuron, resulting in muscle atonia while REM-off (monoaminergic neuron in locus ceruleus and raphe nucleus) decreases during REM sleep [adapted from Benarroch, 2006]
