Physiology of sleep

Rest – definition: relaxation, mental & physical calmness

Sleep – definition: altered state of consciousness, very little physical activity, slowing of body's

physiological processes

1. Physiology of sleep

   A. Facilitates reflex (reticular activating system "RAS") & voluntary movements

   B. Controls cortical activities related to state of alertness

   C. Bulbar synchronizing region works with RAS to control cyclic nature of sleep

   D. Hypothalamus – control center for sleeping & walking (injury to hypothalamus: person will

   sleep for abnormally long time)

   E. Neurotransmitters in brain – some excite: norepinephrine, histamine, acetylcholine, serotonin,

   and dopamine. some inhibit: GABA

   F. wakefulness occurs when peripheral sensory organs & cerebral cortex activates

2. Stages of sleep – Non-rapid eye movement (NREM)

   A. Stage I 5-10 minutes, transition between wakefulness & sleep, easily awakened, relaxed,

   aware of surroundings, regular deep breathing, 5% of total sleep time

   B. Stage II 10-15 minutes, light sleep, easily aroused physiologic changes to temp., BP.,

   HR, all ↓slightly. 50% of total sleep time.

   C. Stage III 5-15 minutes. deep sleep, difficult to arouse, parasympathetic N.S. causes temp.,

   pulse, resp., BP., to slow even more. skeletal muscles relaxed. 10% of total sleep time.

   D. Stage IV 20-50 minutes. (Delta). difficult to awaken, arousal threshold is greatest, body,

   mind, muscles relax. parasympathetic causes temp., BP ↓. If aroused, person is confused.

   10% total sleep time.

3. Stages of sleep – Rapid eye movement (REM)

   A. less restful than NREM

   B. eyes move rapidly, small muscles twitch, GI secretions ↑, large muscle activity & deep

   tendon reflex depression, dreaming, metabolism, BP, pulse ↑, breathing rapid, irregular,

   apnea may occur

4. Sleep cycle

   A. the person passes consequently through four stages of NREM sleep

   B. pattern is reversed – return from stage IV to III to II

   C. then enter REM sleep instead of reentering stage I

   D. the person reenters NREM sleep at stage II and moves on to III and IV

   E. if sleep is interrupted, person goes to stage IA Single Normal Sleep Cycle:

   Wakefulness→NREM Stage I→NREM Stage II→NREM Stage III→NREM Stage IV→

   NREM Stage III→NREM Stage II→REM→NREM Stage II