Physiology of sleep

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physiology,sleep,EEG,medical teachers


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1 PHYSIOLOGY OF SLEEP Dr.Dharitri Parmar

How do we Measure Sleep?:

2 How do we Measure Sleep? Electroencephalogram (EEG) measures the electrical changes in the brain. The electrodes are placed on the scalp. The wavy lines recorded by the EEG are called brain waves. Electrooculogram (EOG) measures the electrical changes as the eyes rotate in its socket. The electrodes are placed either above and below the eye or left and right of the eye. Electromyogram (EMG) measures the electrical changes generated during muscle contraction. The electrodes are placed under the chin. EEG, EOG and EMG are recorded simultaneously and the patterns of activity in these three systems provide basic classification for the different types of sleep. Placement of electrodes to determine EEG,EOG and EMG

Placement of electrodes of polysomnographic measurement:

3 Placement of electrodes of polysomnographic measurement

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4 Brain, eye and muscle wave in NREM sleep have greater amplitudes and lower frequencies as compared to REM and wakefulness. The amplitude increases continuously, while their frequency decreases correspondingly from the time a normal person falls asleep, till he or she reach the deepest NREM sleep.

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5 Types of brain waves.

Classification of Brain Waves:

6 EEG associated with sleep from the highest to the lowest frequency: Beta waves (β) The frequency of beta waves range from 13-15 to 60 hertz (Hz) and an amplitude of 30 microvolt (μV). Beta waves are associated with wakefulness. Alpha waves (α) The frequency range from 8 to 12 Hz and an amplitude of 30 to 50 μV. These waves are found in people who have their eyes closed and relax or meditating. Theta waves (θ) Frequency in the range of 3 to 8 Hz and amplitude of 50 to 100 μV. These waves are related with memory, emotions and activity in the limbic system. Delta waves (δ) It ranges from 0.5 to 4 Hz in frequency and amplitude of 100 to 200 μV. Scientists had observed delta waves in deep sleep and in coma patients because normal and healthy adults will not show large amount of delta waves. Flat-line trace occurs when no brain waves are present and this is the clinical sign of brain death. Classification of Brain Waves


7 STAGES OF SLEEP Sleep is characterized by two distinct cycles, NREM sleep. Non-Rapid Eye Movement Sleep (NREM) is further classified into 4 stages: Stage 1, Stage 2, Stage 3 and Stage 4. Rapid Eye Movement Sleep (REM) sleep Stages 3 and 4 in humans are homologous to animal sleep stage of slow-wave sleep (SWS). A normal human sleep cycle starts with NREM stage 1, stage 2, stage 3, stage 4 and progresses to REM. This cycle is repeated several times throughout the night (between 4 to 5 cycles). The duration for each cycle has been identified ranging between 60 to 90 minutes. The next section explains the characteristics of each of the four stages in detail.

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Features of NREM Sleep Stages:

9 Features of NREM Sleep Stages Stage 1 NREM sleep begins when a person close his eyes, followed by several sudden sharp muscles contractions in the legs then relaxation. As he continues falling asleep the rapid beta waves of wakefulness are replaced by the slower alpha waves and soon the slower theta waves start to emerge. This is the stage, which is when human get lightest sleep and could wake up easily external environment. Each period of stage 1 sleep generally lasts 3 to 12 minutes.

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10 Stage 2 This is the stage of light sleep in which the frequency of the EEG decreases and amplitude increases. The theta waves of this stage are interrupted by a series of high frequency waves known as sleep spindles and they last for 1 to 2 seconds. These waves are generated by interactions between thalamic and cortical neurons. During this stage the EEG traces show high amplitude wave forms called K-complex. This is the stage where adults spend the greatest proportion of about 50% of the total time in sleep each night. Sleep spindles and K-complex are features of stage 2 NREM sleep.

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11 Stage 3 This is the stage from moderate to true deep sleep (SWS). As delta waves first appear , sleep spindles and K-complexes occur, but are less common compared to in stage 2. Stage 3 lasts for 10 minutes during the first sleep cycle and represents only 7% of the total night’s sleep.

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12 Stage 4 This is the deepest NREM sleep. The EEG trace is dominated by delta waves and overall neural activity is at its lowest. Breathing, heart rate, blood pressure and brain’s temperature are all reduced under the influence of parasympathetic nervous system. This is also the stage in which children may have episodes of somnambulism or sleepwalking and night terrors .

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Rapid Eye Movement Sleep:

14 Rapid Eye Movement Sleep Rapid Eye Movement Sleep (REM) or paradoxical sleep constitutes 20-25% of total sleeping time. Over the course of a night’s sleep, a person will experience 4 to 5 periods of REM sleep. EEG recording of neural activity during REM shows almost the same tracing as to that during waking hours. There are no dominating brains waves during this stage of sleep. REM sleep is characterized with rapid movement of the eyes in its sockets, near-total muscle paralysis and changes in breathing and heart rates. However, most people will wake up easily during this period if there are any external disturbances. This is because REM sleeps happens to be the period of very light sleep.

Comparing NREM and REM:

15 Comparing NREM and REM NREM is an active state that is maintained partly through oscillations between the thalamus and the cortex. The three major oscillations systems are sleep spindles, delta oscillations and slow cortical oscillations. REM sleep is generated by the cholinergic mediated “REM-on neurons” in the mesencephalic and pontine cholinergic neurons. It is characterized by muscle hypotonia, cortical activation, low-voltage desynchronization of the EEG and rapid eye movements.

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16 NREM SLEEP (SWS) No dreaming /logical subconscious thinking Decrease in RR,HR,BP EEG shows transition from fast, low amplitude waves to slow, high amplitude waves Ach &/or dopamine Easy to arose person Pulsatile release of GH, gonadotropins from AP REM SLEEP (PARADOXICAL) Associated with dreaming (3 /night,longer,fantacy world)) Increased/irregular RR,HR,BP.Penile erection orclitoris engorgement, muscle twiches EEG is synchronised NE &/or serotonin Difficult to arose

Biological Rhythms :

17 Biological Rhythms Biological processes related to sleep are influenced by the circadian rhythm and other biology rhythms. Homeostatic factors (factor S) and circadian factors (factor C) are both interact to determine the timing and quality of sleep.

Which NTs have been shown to be important for wakefulness? :

18 Which NTs have been shown to be important for wakefulness? • acetylcholine • histamine • serotonin (5HT) • norepinephrine • dopamine • orexin/hypocretin

Which pathway inhibits the normal wakefulness pathways? :

19 Which pathway inhibits the normal wakefulness pathways? VLPO neurons via GABA inhibit these nuclei which promote wakefulness: TMN (histamine) SN and VTA (DA) LC (NE) PPT and LDT (Ach) DR(5HT)

Circadian Rhythms :

20 Circadian Rhythm is one of the several intrinsic body rhythms modulated by the hypothalamus. The suprachiasmatic nucleus sets the body clock to 24 hours and is modulated by light exposure. The retino-hypothalamic tract allows light cues to directly influence the suprachiasmatic nucleus. Circadian rhythm allows the brain to regulate periods of rest during sleep (equivalent to battery re-charging) and periods of high activity during the wakefulness (equivalent to battery discharging). The nadir of the rhythm is in the early morning. The downswing in circadian rhythm after the apex in early evening is thought to initiate sleep and maintain sleep overnight for full restoration by preventing premature awakening. The morning upswing then facilitates awakening and acts as a counterbalance to the progressive discharge of wake neuronal activity, enabling cognitive function throughout wakefulness. Circadian Rhythms

Other Biological Rhythms:

21 Other Biological Rhythms The hypothalamus controls the body temperature cycles. Body temperature will increase during the course of the day and decrease during the night. The temperature peaks and troughs are thought to mirror the sleep rhythm. People who are most alert late in evening have body temperature peaks later in the evening compared to those who are most alert early in the morning. Melatonin secretion by the pineal gland controlled by the suprachiamastic nucleus is light-modulated. It is secreted maximally during the night. Prolactin, testosterone, and growth hormone also demonstrate circadian rhythms, with maximal secretion during the night. Melatonin influences sleep timing by modulating the amplitude of circadian signal and neuronal firing [1] . Melatonin has multiple functions throughout the body, including regulation of immune function, hormone secretion, reproductive rhythms.

Neuroendocrine Regulation of Sleep Stages:

22 Neuroendocrine Regulation of Sleep Stages Growth hormone-releasing hormone (GHRH) and corticotrophin-releasing hormone (CRH) are the primary hormones in sleep regulation by inverse action [2] . GHRH is circadian rhythm dependant and levels increase at night. GHRH promotes NREM while GH inhibits the production of hormones from the hypothalamus, pituitary and adrenal glands (HPA). There is a reciprocal concentration level in neuroendocrines during the sleep cycle. When GHRH concentration is high, it will promote NREM/SWS sleep, corticotrophin (ACTH) and cortisol will be at its lowest concentration levels. GHRH and ghrelin promotes the synthesis of GH which promotes tissue growth and protein anabolism. CRH has an opposite effect and inhibits the effect of GHRH sleep promotion

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23 Other peptides and steroids involved with sleep regulation: Insulin-like growth factor (IGF-1) suppresses GH secretion which leads to sleep suppression Somatostatin is observed in REM and it’s effect includes reduction of NREM and GH .The effect of Somatostatin is more pronounced in the elderly causing sleep impairment by the reduction in GHRH production. Excessive cortisol has been linked (exp. Cushing’s disease patients) with the decrease SWS and more disrupted sleep . Cortisol levels differ with gender and age . Vasopressin itself has beneficial effects of increasing the total sleep time, SWS and REMS . Unfortunately Vasopressin when combined with CRH during activation of stress reaction increases wakefulness. Ghrelin has a similar effect to GHRH in promoting SWS and together with GHRH encourages the increase of GH level.

Interaction and involvement of GHRH, GH, CRH, Cortisol in Sleep stages. :

24 Interaction and involvement of GHRH, GH, CRH, Cortisol in Sleep stages.

Brain Regulated Sleep:

25 Brain Regulated Sleep The brain controls when a person wakes up and when one sleeps. The region of the brain that is in charge of controlling sleep is located in the POSTERIOR HYPOTHALAMUS. The hypothalamus is also the region controlling the circadian rhythm and sensitive to light stimuli and temperature. The “switch” for sleep is considered to be the ventrolateral preoptic nucleus (VLPO) OF THE ANTERIOR HYPOTHALAMUS. This area becomes active during sleep. The VLPO containing the GABAnergic and galanergic neurons are responsible for normal sleep. These neurons contain both the GABA-synthesizing enzyme glutamic acid decarboxylase and the peptide galanin.

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26 The Cortical Activation That Is Important To Keep People Awake Consisting Of Posterior Hypothalamus, the intralaminar thalamus and the basal telencephalon. This network of the lower brainstem controls wakefulness. Neurons that responsible in this region are named orexin or hypocretin neurons. Both regions act in a counter balance action

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27 The modulatorly systems can be divided into two major pathways – the ventral (reticulo-hypothalamic-cortical) pathway) and the dorsal (reticulo-thalamic-cortical) pathway. To maintain wakefulness of these two pathways, acetylcholine and glutamate are the main neurotransmitters. The brainstem controls REM-NREM sleep through a cholinergic-aminergic interaction. dopaminergic system is contributory to sleep regulation. These GABAnergic neurons are most active during NREM and inactive during REM and wakefulness. Electrical stimulation of these neurons causes sleep and their destruction causes insomnia.

Proportional aminergic and cholinergic activity in various stages of sleep. :

28 Proportional aminergic and cholinergic activity in various stages of sleep.

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29 Serotonergic nuclei of the anterior raphe which is active during wakefulness produces serotonin and causes its own inhibition through a negative feedback loop, when the individual has been awake for a certain time leads to sleep. Signals of REM sleep originate in the pontine reticular formation and are transmitted to the motor layers of the superior colliculi. The collicular neurons in turn send projections to the paramedian pontine reticular formation which coordinates the duration and the direction of the eye movements. During REM sleep ,the pontogeniculooccipital (PGO) spikes that occur intermittently orginating in the pontine reticular formation. In the absence of PGO, REM sleep can be generated by the stimulation of the Pons with acetylcholine especially in the peribrachial areas of the Pons


30 DREAMING Dreams are the images, sounds, thoughts and feelings experienced during sleeping. There is a strong association with REM sleep. Scientific studies of dreams, also known as ONEIROLOGY, have shown that a person spends a total of six years dreaming (estimated at 2 hrs each night). Activation Synthesis Theory of Dreams There are many theories on dreaming. The activation synthesis theory asserts that the sensory experiences are fabricated by the cortex as a means of interpreting chaotic signals from the pons. In the ascending cholinergic PGO (ponto-geniculo-occipital) waves stimulate the higher midbrain and forebrain cortical structures, producing rapid eye movements. The activated forebrain then synthesizes the dream out of this generated information. Some researchers suggest that dreams are generated in the forebrain, and that REM sleep and dreaming are not related directly. Some patients with brain stem damage experience loss in ability to dream.

Dreams & Memory:

31 Dreams & Memory Study have shown that illogical locations, characters and dream flow may help the brain strengthen the linking and consolidation of semantic memories. These occur during REM sleep when the flow of information between the hippocampus and neocortex is reduced. One stage of memory consolidation is the linking of distant but related memories. It is found that people all over the world dream of mostly the same things. Personal experiences from the last day or week are frequently incorporated into dreams Emotions Sexual content Recurring dreams Common themes Relationship with mental illness

Functional Hypotheses of Dreaming:

32 Functional Hypotheses of Dreaming There are several hypotheses about the function of dreams which includes: During the night there may be many external stimuli bombarding the senses, the mind interprets the stimulus and makes it a part of dream in order for a continued sleep. Bad dreams let the brain learn to gain control over emotions resulting from distressing experiences. Dreams are like the cleaning-up operations of computers when they are in off-line, removing parasitic nodes and other “junk” from the mind during sleep. Dreams regulate mood. Dream is a product of “dissociated imagination”.

Progression of Sleep for the Fetus :

33 Progression of Sleep for the Fetus In maternal womb, lies the beginning of life from a small neonate to fetus which goes through various stimulating and interactive to the environment. The fetus will never feel isolated as its activities in the womb never ceases, the fetus will move around, response to noise and light, and finally take most of the time to sleep. It is a fact that fetus spends a remarkable portion of time sleeping with approximately around 80% of their day in active sleep or REM stage while the remainder of their time is spent in quiet sleep or NREM sleep and wakefulness. Around the 32th week, the fetus still spends 90 to 95% of the day in deep sleep, some in REM sleep, and some in an indeterminate state. During REM sleep, the fetus' eyes move back and forth just as how adult's eyes do, and many researchers believe that it is dreaming. Closer to birth, the fetus sleeps for between 85 to 90% of the time, this is almost equivalent to a newborn. They will alternate between wakefulness and sleeping. Between its frequent naps.

Development of a Sleep Cycle for the Fetus:

34 Development of a Sleep Cycle for the Fetus The first development of sleep and circadian rhythms is found during fetal period. It is only noticeable during the last trimester of gestation. The earliest form of sleep is known as active sleep which is an immature form of REM sleep . It is then followed by quiet sleep, which is NREM stage with immature form of slow-wave sleep (SWS) when the REM sleep diminishes its predominance during fetal development. The period of wakefulness for fetus can be observed by the movements of limbs such as stretching, kicking and even yawning observed through 4 dimensional sonography. These make up the cycle of a fetus daily life.

Progression of Sleep for Infants :

35 Progression of Sleep for Infants Newborns sleep around 70% of their daily life, on and off, all throughout the day and night. This constitutes as much as 16 hours a day or even more. They go through a complete sleep cycle about every 50-60 minutes, so they are apparently in light sleep and may wake up many times each night. Sleep behavior tends to change substantially during the first few weeks of life. By 2 to 4 months most babies will sleep 6 to 8 hours through the night and by age 6 months, they can sleep for longer periods of about 10-12 hours. During this time, they spend only 20-30% of their time in REM sleep , with the remainder equally spent in NREM sleep and wakefulness. For infants and babies, napping is also part of their sleeping needs. In early infancy, napping usually occurs 2 to 4 times daily. Each nap should take about 0.5 to 2 hours. At the age of 6 to 9 months, they will reduce by taking only 2 naps in a day. By the 18th month, they will probably take only one nap a day.

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36 Age Nighttime Sleep (hrs) Daytime Sleep (hrs) Total Sleep (hrs) 1 month 8.5 (many naps) 7.5 (many naps) 16 3 months 6-10 5-9 15 6 months 10-12 3-4.5 14.5 9 months 11 3 (2 naps) 14 12 months 11 2.5 (2 naps) 14.5 18 months 11 2.5 (1-2 naps) 14.5

Sleep Disorders in Infants :

37 Sleep Disorders in Infants Babies have different phases of sleep: drowsiness, REM sleep, light sleep, deep sleep, and very deep sleep . As babies grow, their periods of wakefulness increase and in the contrast, the periods of REM and NREM will also decrease. All babies wake during the night, this is a biological fact rather that a problem. This is because they have more periods of REM sleep. However, problem arises when most parents will notice that their baby will have sleep onset associations , as this is the most common cause of babies not being able to settle back to sleep. They are likely to be pampered to sleep, like being rocked or a sucking a pacifier to enable them to fall back to sleep. As a result, many young children become unable to fall asleep on their own. They rely on their parents’ help instead of learning to comfort themselves. One more sleeping disorder that is prevalent among infants and babies is sleep apnea . This involves unexplained lapses in breathing and snoring may be also one symptom of apnea .

Sleep for Pre-Schoolers:

38 Sleep for Pre-Schoolers Generally, pre-school children need about 10 to 13 hours of sleep a night. It is more important that parents train the child to maintain a routine bedtime rather than the total time the child spends sleeping at this stage. Naps are also not necessary for pre-school children as they are getting more active; they are more likely to be fascinated by TV programs, and play with toys and games.

Sleep for Schooling Adolescents :

39 Sleep for Schooling Adolescents School-aged children still need between 9 and 12 hours of sleep at night. Here are some guidelines of schooling age: Can fall asleep within 15 to 30 minutes. Can wake up easily at the time they need to get up and don't need others to keep bugging them to get up. Awake and alert all day and don't need naps during the day. As adolescents progress through puberty, they actually need more sleep. In the biological point of view, the serum levels of melatonin which is a sleep inducing hormone will be rising before sleep onset. For most adolescence, the timing of melatonin release is later at night, rendering teenagers unable to fall asleep before 10.30pm.

Sleep Deprivation in Adolescents :

40 Sleep Deprivation in Adolescents sleep deprivation can lead to: Decreased attentiveness or concentration Decreased short-term memory Inconsistent performance Delayed response time

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41 Adults need around 7 to 8 hours sleep everyday. Adult age encompasses the widest range of human life cycle. As such, it is important to ensure good quality of sleep everyday to be productive at work.