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Physiological Basis of Sleep and Wakefulness

Neurophysiology of sleep and wakefulness
• Physiological Basis of Sleep and Wakefulness • Aug 22 07

The neurophysiology of sleep and wakefulness is complex, but is the result of the superimposition of higher neurological control over lower functions [23, 24, 25] (

 

Neuroanatomy of sleep and wakefulness
• Physiological Basis of Sleep and Wakefulness • Aug 22 07

The activity of the cerebral cortex is critical in determining whether sleep or wakefulness occurs, but it does not generate the drive to enter sleep or wakefulness.

This is due to the…


 

Sleep rhythms
• Physiological Basis of Sleep and Wakefulness • Aug 22 07

The diurnal cycling of sleep–wake rhythms maintains sleep and wakefulness in line with environmental time, but by itself is insufficient to initiate sleep (

Fig. 2.8).

Loss of function of…


 

Pineal gland - Circadian rhythms
• Physiological Basis of Sleep and Wakefulness • • Circadian rhythms • Aug 22 07

The pineal gland contains a circadian pacemaker in some vertebrates, such as perching birds (passerines).

In humans this function is taken over by the SCN in the anterior hypothalamus, which controls the…


 

Output from SCN - Circadian rhythms
• Physiological Basis of Sleep and Wakefulness • • Circadian rhythms • Aug 22 07

Fibres leave the SCN to reach the ventrolateral preoptic area (VLPO) of the anterior hypothalamus multisynaptically. They initially relay in the sub-paraventricular zone before synapsing predominantly in the dorsomedial nucleus of…


 

Coordination of circadian rhythms
• Physiological Basis of Sleep and Wakefulness • • Circadian rhythms • Aug 22 07

The clock in the SCN, through its neurological connections, has a circadian influence not only on sleep, but also on temperature control, hormone secretion and other functions. The multisynaptic processing of the SCN…


 

Melatonin - Circadian rhythms
• Physiological Basis of Sleep and Wakefulness • • Circadian rhythms • Aug 22 07

Melatonin production
Melatonin (N-5-methoxy-N-acetyl-tryptamine) is synthesized from tryptophan after it has been converted to 5HT [17].

Its synthesis can be increased by oral tryptophan or vitamin B6, a coenzyme…


 

Circadian rhythms
• Physiological Basis of Sleep and Wakefulness • • Circadian rhythms • Aug 22 07

Circadian rhythm periodicity
Circadian rhythms have a periodicity of around a day, which is longer than ultradian rhythms of,  for instance, REM sleep and shorter than infradian rhythms such as the menstrual cycle. The…


 

Input to SCN - Circadian rhythms
• Physiological Basis of Sleep and Wakefulness • • Circadian rhythms • Aug 22 07

Impulses reach the SCN from retinal receptors which lie particularly in the lower and nasal quadrant of the retina. The receptors are the retinal ganglion cells and their light-sensitive pigment is…


 

SCN clock genetics - Circadian rhythms
• Physiological Basis of Sleep and Wakefulness • • Circadian rhythms • Aug 22 07

The characteristics of this rhythm generator are largely genetically determined. At least 12 genes have been identified on chromosome 5 which, through inhibiting or promoting protein transcription, form a complex negative…


 

REM sleep ultradian rhythm
• Physiological Basis of Sleep and Wakefulness • Aug 22 07

REM sleep is almost never normally entered from wakefulness except in infants. It is preceded by NREM sleep, usually stages 1 and 2. It can therefore be regarded as a type of arousal…


 

Control of sleep and wakefulness
• Physiological Basis of Sleep and Wakefulness • Aug 22 07

Whether an individual is awake or asleep depends on the balance of forces promoting and inhibiting each of these two states [11].

At times the balance can be almost…


 

Adaptive drive
• Physiological Basis of Sleep and Wakefulness • Aug 22 07

This includes a variety of mechanisms that influence sleep but which are independent of the time spent awake and of circadian and ultradian rhythms. They modify the sleep–wake cycle according to changes in the environment…


 

Rapid eye movement (REM) sleep - Genito-urinary function
• Physiological Basis of Sleep and Wakefulness • • Rapid eye movement (REM) sleep • Aug 21 07

Genito-urinary function
Sleep-related erections (nocturnal penile tumescence) develop rapidly during REM sleep, and may persist into NREM sleep.

Their frequency is not affected by sexual abstinence…


 

Non-rapid eye movement (NREM) sleep - Cardiovascular function
• Physiological Basis of Sleep and Wakefulness • • Non-rapid eye movement (NREM) sleep • Aug 21 07

Even before the onset of NREM sleep the heart rate falls in parallel with the reduction in body temperature and is related to the fall in metabolic rate. Vasodilatation…


 

Non-rapid eye movement (NREM) sleep - Genito-urinary function
• Physiological Basis of Sleep and Wakefulness • • Non-rapid eye movement (NREM) sleep • Aug 21 07

Genito-urinary function
There is considerable diurnal variation in renal function. Water and sodium are retained at night and of the 1–2l of urine that is normally excreted…


 

Rapid eye movement (REM) sleep - Cardiovascular function
• Physiological Basis of Sleep and Wakefulness • • Rapid eye movement (REM) sleep • Aug 21 07

Homeostatic control of cardiovascular function in response to, for instance, changes in blood volume or temperature is poor in REM sleep. There is considerable variability of heart rate and…


 

Rapid eye movement (REM) sleep - Respiratory function
• Physiological Basis of Sleep and Wakefulness • • Rapid eye movement (REM) sleep • Aug 21 07

The minute ventilation is reduced compared to NREM sleep and wakefulness [9], and the arterial Pco2 rises by 2–5mmHg. Arousal in response to stimulation from mechanoreceptors in…


 

Non-rapid eye movement (NREM) sleep - Gastrointestinal function
• Physiological Basis of Sleep and Wakefulness • • Non-rapid eye movement (NREM) sleep • Aug 21 07

Less saliva is produced during sleep than during wakefulness, possibly partly related to a reduction in oromotor activity, but the volume is similar in NREM and REM sleep. The…


 

Non-rapid eye movement (NREM) sleep - Respiratory function
• Physiological Basis of Sleep and Wakefulness • • Non-rapid eye movement (NREM) sleep • Aug 21 07

The minute ventilation falls (1.23) and the arterial Pco2  rises by 2–3mmHg. The stage of NREM sleep oscillates frequently at sleep onset and the threshold for carbon dioxide to…


 
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