Physiology Of Sleep | Physiology | General Medicine

PHYSIOLOGY OF SLEEP :
Sleep is the natural periodic state of rest for mind and body with closed eyes characterized by partial or complete loss of consciousness.
Loss of consciousness leads to decreased response to external stimuli and decreased body movements.
Depth of sleep is not constant throughout the sleeping period. It varies different stages of sleep.

SLEEP REQUIREMENT:
Sleep requirement is not constant. However, average sleep requirement per day at different age group is:
Newborn infants: 18 to 20 hours
Growing children: 12 to 14 hours
Adults: 7 to 9 hours
Old persons: 5 to 7 hours

TYPES OF SLEEP:
Sleep is of two types:

1. RAPID EYE MOVEMENT SLEEP – REM SLEEP: Rapid eye movement sleep is the type of sleep associated with rapid conjugate movements of the eyeballs, which occurs frequently.
Though the eyeballs move, the sleep is deep. So, it is called paradoxical sleep. It occurs about 20% to 30% of the sleeping period. Functionally, REM sleep is very important because it plays an important role in the consolidation of memory. Dreams occur during this period.

2. NON – RAPID EYE MOVEMENT SLEEP – NERM OR NON – REM SLEEP: Non-rapid eye movement (NERM) sleep is the type of sleep without the movement of eyeballs. It is also called slow – wave sleep. Dreams do not occur in this type of sleep and I occupy about 70% to 80% of total sleeping period. Non – REM sleep is followed by REM sleep.

PHYSIOLOGICAL CHANGES DURING SLEEP:
During sleep, most of the body functions are reduced to the basal level.

1. PLASMA LEVEL:
Plasma volume decreases by about 10% during sleep.

2. CARDIOVASCULAR SYSTEM:
During sleep, the heart rate reduces. It varies between 45 and 60 beats per minute.

3. RESPIRATORY SYSTEM:
Rate and force of respiration are decreased. Respiration becomes irregular and Cheyne – Stokes type of periodic breathing may develop.

4. GASTROINTESTINAL TRACT:
Salivary secretion decreases during sleep. Gastric secretion is not altered or may be increased slightly. Contraction of an empty stomach is more vigorous.

5. EXCRETORY SYSTEM:
Formation of urine decreases and the specific gravity of urine increases.

6. SWEAT SECRETION:
Sweat secretion increases during sleep.

7. LACRIMAL SECRETION:
Lacrimal secretion decreases during sleep.

8.MUSCLE TONE:
The tone in all the muscles of the body except ocular muscles decreases very much during sleep. It is called sleep paralysis.

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