Question

describe the cycle of our circadian rhythm and identify some events that can disrupt this biological clock. List all stages of sleep cycle and explain each how they differ as far as sleep disorders

Answer 1

Circadian rhythm refers to the rhythmic fluctuations in cer-
tain physiological parameters of the body. These are called circadian rhythms because they often show 24 h cycles (circadian around a day). Many of the rhythms are co-ordinated with each other .

Disturbances of circadian rhythm can occur during high
speed jet travel. One may travel several thousand kilometres within a few hours. As a result, the traveller’s external clock (day or night) does not coincide with the internal biological clock. That is, the body may be in rest (night) phase, while it is day time in the country of destination. It results in irritability , mental depression or even physical illness. The symptoms subside in a few days. The condition is called jet lag.

STAGES OF SLEEP AND EEG PATTERN RAPID EYE MOVEMENT SLEEP
During REM sleep, electroencephalogram (EEG) shows irregular waves with high frequency and low amplitude. These waves are desynchronized waves.
NON-RAPID EYE MOVEMENT SLEEP
The NREM sleep is divided into four stages, based on the EEG pattern. During the stage of wakefulness, i.e. while lying down with closed eyes and relaxed mind, the alpha waves of EEG appear. When the person proceeds to drowsy state, the alpha waves diminish.
Stage I: Stage of Drowsiness
Alpha waves are diminished and abolished. EEG shows only low voltage fluctuations and infrequent delta waves.
Stage II is characterized by spindle bursts at a fre- quency of 14 per second, superimposed by low voltage delta waves.
Stage III: Stage of Medium Sleep
During this stage, the spindle bursts disappear. Fre- quency of delta waves decreases to 1 or 2 per second and amplitude increases to about 100 μV.
State IV: Stage of Deep Sleep
Delta waves become more prominent with low frequency and high amplitude.

SLEEP DISORDERS
1. INSOMNIA
Insomnia is the inability to sleep or abnormal wake- fulness. It is the most common sleep disorder. It occurs due to systemic illness or mental conditions such as psychiatric problems, alcoholic addiction and drug addiction.
2. HYPERSOMNIA
Hypersomnia is the excess sleep or excess need to sleep. It occurs because of lesion in the floor of the third ventricle, brain tumors, encephalitis, chronic bronchitis and disease of muscles. Hypersomnia also occurs in endocrine disorders such as myxedema and diabetes insipidus.
3. NARCOLEPSYANDCATAPLEXY
Narcolepsy is the sudden attack of uncontrollable sleep. Cataplexy is sudden outburst of emotion. Both the diseases are due to hypothalamic disorders.
4. SLEEPAPNEASYNDROME
Sleep apnea is the temporary stoppage of breathing repeatedly during sleep. Sleep apnea syndrome is the disorder that involves fluctuations in the rate and force of respiration during REM sleep with short apneic episode. Apnea is due to decreased stimulation of respiratory centers, arrest of diaphragmatic movements, airway obstruction or the combination of all these factors. When breathing stops, the resultant hypercapnia and hypoxia stimulate respiration.
Sleep apnea syndrome occurs in obesity, myx- edema, enlargement of tonsil and lesion in brainstem. Common features of this syndrome are loud snoring , restless movements, nocturnal insomnia, daytime sleepiness, morning headache and fatigue. In severe conditions, hypertension, right heart failure and stroke occur.
5. NIGHTMARE
Nightmare is a condition during sleep that is characterized by a sense of extreme uneasiness or discomfort or by frightful dreams. Discomfort is felt as of some heavy weight on the stomach or chest or as uncontrolled movement of the body. After a period of extreme anxiety, the subject wakes with a troubled state of mind. It occurs mostly during REM sleep. Nightmare occurs due to improper food intake, digestive disorders or nervous disorders. It also occurs during drug withdrawal or alcohol withdrawal.
6. NIGHT TERROR
Night terror is a disorder similar to nightmare. It is common in children. It is also called pavor nocturnus or sleep terror. The child awakes screaming in a state of fright and semiconsciousness. The child cannot recollect the attack in the morning. Nightmare occurs shortly after falling asleep and during non-REM sleep. There is no psychological disturbance.
7. SOMNAMBULISM
Somnambulism is getting up from bed and walking in the state of sleep. It is also called walking during sleep or sleep walking (somnus = sleep; ambulare = to walk). It varies from just sitting up in the bed to walking around with eyes open and performing some major complex task. The episode lasts for few minutes to half an hour. It occurs during non-REM sleep. In children, it is associated with bedwetting or night terror without any psychological disturbance. However, in adults it is associated with psychoneurosis.
8. NOCTURNALENURESIS
Nocturnal enuresis is the involuntary voiding of urine at bed. It is also called or bedwetting. It is common in children.
9. MOVEMENT DISORDERS DURING SLEEP
Movement disorders occur immediately after falling asleep. Sleep start or hypnic jerk is the common move- ment disorder during sleep. It is characterized by sudden jerks of arms or legs. Sleep start is a physiological form of clonus.
Other movement disorders are teeth grinding (bruxism), banging the head and restless moment of arms or leg