Physiology of Sleep and its correlation with EEG waves
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Content includes Physiology of sleep and and its correlation with EEG waves along with specific characteristics of different phases of sleep as well as an account of sleep disorders.
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Physiology of Sleep and its correlation with EEG waves
- 1. Physiology of Sleep Dr. Abhilasha Mishra Asst. Proffesor, Physiology department,
- 2. • Sleep ,Unconsciousness from which the person can be aroused by sensory or other stimuli. • Coma, which is unconsciousness from which the person cannot be aroused.
- 3. Two Types of Sleep • (1) slow-wave sleep, • because in this type of sleep the brain waves are very strong and very low frequency, • (2) rapid eye movement sleep (REM sleep), • because in this type of sleep the eyes undergo rapid movements despite the fact that the person is still asleep.
- 4. • Most sleep during each night is of the slow-wave variety; this is the deep, restful sleep that the person experiences during the first hour of sleep after having been awake for many hours. • REM sleep, occurs in episodes that occupy about 25 per cent of the sleep time in young adults; each episode normally recurs about every 90 minutes. • This type of sleep is not so restful, and it is usually associated with vivid dreaming.
- 5. Slow-Wave Sleep • Decrease in both peripheral vascular tone and many other vegetative functions of the body. • There are 10 to 30 per cent decreases in blood pressure, respiratory rate, and basal metabolic rate. • Although slow-wave sleep is frequently called “dreamless sleep,” dreams and sometimes even nightmares do occur during slow-wave sleep. • Dreams of slow-wave sleep usually are not remembered. • Consolidation of the dreams in memory does not occur.
- 7. REM Sleep (Paradoxical Sleep, Desynchronized Sleep) • In a normal night of sleep, bouts of REM sleep lasting 5 to 30 minutes usually appear on the average every 90 minutes.
- 8. Important characteristics of REM sleep • 1. It is usually associated with active dreaming and active bodily muscle movements. • 2. The person is even more difficult to arouse by sensory stimuli than during deep slow-wave sleep, and yet people usually awaken spontaneously in the morning during an episode of REM sleep. • 3. Muscle tone throughout the body is exceedingly depressed, indicating strong inhibition of the spinal muscle control areas. • 4. Heart rate and respiratory rate usually become irregular, which is characteristic of the dream state.
- 9. • Irregular muscle movements do occur. • These are in addition to the rapid movements of the eyes. • The brain is highly active in REM sleep, and overall brain metabolism may be increased as much as 20 per cent. • This type of sleep is also called paradoxical sleep because it is a paradox that a person can still be asleep despite marked activity in the brain.
- 10. • Occurrence of large phasic potentials that originate in the cholinergic neurons in the pons and pass rapidly to the lateral geniculate body and from there to the occipital cortex. They are called pontogeniculo-occipital (PGO) spikes.
- 11. • Positron emission tomography (PET) scans of humans in REM sleep show increased activity in the pontine area, amygdala, and anterior cingulate gyrus, but decreased activity in the prefrontal and parietal cortex. • Activity in visual association areas is increased, but there is a decrease in the primary visual cortex.
- 12. • Organisms in REM sleep suspend central homeostasis, allowing large fluctuations in respiration, thermoregulation, and circulation which do not occur in any other modes of sleeping or waking. • The body abruptly loses muscle tone, a state known as REM atonia.
- 14. Basic Theories of Sleep • An earlier theory of sleep was that the excitatory areas of the upper brain stem, the reticular activating system, simply fatigued during the waking day and became inactive as a result. This was called the passive theory of sleep.
- 15. Sleep Is Believed to Be Caused by an Active Inhibitory Process. • There seems to be some center located below the midpontine level of the brain stem that is required to cause sleep by inhibiting other parts of the brain.
- 16. • Neuronal Centers, Neurohumoral Substances, and Mechanisms That Can Cause Sleep— A Possible Specific Role for Serotonin • Stimulation of several specific areas of the brain can produce sleep with characteristics near those of natural sleep.
- 17. • 1. The most conspicuous stimulation area for causing almost natural sleep is the raphe nuclei in the lower half of the pons and in the medulla. • These nuclei are a thin sheet of special neurons located in the midline. • Nerve fibers from these nuclei spread locally in the brain stem reticular formation and also upward into the thalamus, hypothalamus, most areas of the limbic system, and even the neocortex of the cerebrum.
- 18. • Many nerve endings of fibers from these raphe neurons secrete serotonin. • When a drug that blocks the formation of serotonin is administered to an animal, the animal often cannot sleep for the next several days. • Therefore, it has been assumed that serotonin is a transmitter substance associated with production of sleep.
- 20. • 2. Stimulation of some areas in the nucleus of the tractus solitarius can also cause sleep. • 3. Stimulation of several regions in the diencephalon can also promote sleep, including • (1) the rostral part of the hypothalamus, mainly in the suprachiasmal area • (2) an occasional area in the diffuse nuclei of the thalamus.
- 21. • Lesions in Sleep-Promoting Centers Can Cause Intense Wakefulness. • Discrete lesions in the raphe nuclei lead to a high state of wakefulness. • This is also true of bilateral lesions in the medial rostral suprachiasmal area in the anterior hypothalamus.
- 22. • In both instances, the excitatory reticular nuclei of the mesencephalon and upper pons seem to become released from inhibition, thus causing the intense wakefulness. • Indeed, sometimes lesions of the anterior hypothalamus can cause such intense wakefulness that the animal actually dies of exhaustion.
- 23. • muramyl peptide, a low-molecular-weight substance that accumulates in the cerebrospinal fluid and urine in animals kept awake for several days.
- 24. Possible Cause of REM Sleep. • Why slow-wave sleep is broken periodically by REM sleep is not understood. • However, drugs that mimic the action of acetylcholine increase the occurrence of REM sleep.
- 25. Cycle Between Sleep and Wakefulness • When the sleep centers are not activated, the mesencephalic and upper pontile reticular activating nuclei are released from inhibition, which allows the reticular activating nuclei to become spontaneously active. • This in turn excites both the cerebral cortex and the peripheral nervous system, both of which send numerous positive feedback signals back to the same reticular activating nuclei to activate them still further.
- 27. Physiologic Effects of Sleep • We might postulate that the principal value of sleep is to restore natural balances among the neuronal centers. • The specific physiologic functions of sleep remain a mystery, and they are the subject of much research.