Define Sleep
- State of partial unconsciousness from which a person can be aroused by stimulation
- With the onset of sleep, the RAS nuclei cease activity; cells in the thalamus and cortex become hyperpolarized and insensitive to synaptic input; consciousness is lost
- Cortical activity is depressed (except during REM sleep) but brain stem activity continues
What are the two major types of sleep?
Non-rapid eye movement (NREM)
&
Rapid eye movement (REM)
Always four stages of NREM sleep, followed by REM sleep; repeated in sequence
What are the stages of NREM (NonRapid Eye Movement) sleep?
Stage 1
Stage 2
Stage 3
Stage 4
Describe Stage 1 NREM sleep
Stage 1 - eyels are closed and relaxation begins; the EEG shows alpha waves; one can be easily aroused (will often not realize that one has been asleep)
Describe Stage 2 NREM sleep
Stage 2 - EEG pattern is irregular with sleep spindles (high-voltage wave bursts);
arousal is more difficult
Describe Stage 3 NREM sleep
Stage 3 - sleep deepens; theta & delta waves appear; vital signs decline; some dreaming is common
Describe Stage 4 NREM sleep
Stage 4 - EEG pattern is dominated by delta waves; skeletal muscles are relaxed; arousal is difficult
Which stages of sleep are considered to be most restorative and deep?
- Stages 3 & 4
- they allow hormone output required for cellular repair & immune system function
- Sleep-walking, bed-wetting, and night-terrors occur during these stages
- – typically ends by puberty; adult sleep-walking often associated with drug / alcohol misuse or degenerative disorder
- Sense of muscles “jerking” occurs during Stage 4
What are the stages of REM (Rapid Eye Movement) sleep?
Brain stem nuclei become active again, causing depolarization of cortical neurons
EEG pattern reverts to the stage 1 pattern (alpha waves resembles the awake but relaxed brain)
Vital signs increase and greatest brain oxygen usage occurs
Skeletal muscles (except ocular muscles) are inhibited (RAS dampened)
Most dreaming takes place
What happens to the skeletal muscles during REM sleep?
- The cortex can process information and vivid dreams occur, but there is no motor output or sensory input
- Exception: front eye field not affected (thus rapid eye movements)
- Most dreaming takes place
- Awakened during REM sleep, temorary paralysis
What is the importance of REM sleep?
REM sleep may be a reverse learning process where superfluous info is purged from the brain
sorting out of emotional components and conflicts
Those deprieved of REM sleep may become moody and depressed.
Describe sleep patterns
Alternating cycles of sleep and wakefulness reflect a natural circadian rhythm
Approximately 90 minutes in length
KEY: sleep 1.5, 3, 4.5, 6, or 7.5 hours for best initial wakefulness
Although RAS activity declines in sleep, sleep is more than turning off RAS
Brain is actively guided into sleep my nuclei of the hypothalamusTwo nuclei (suprachiasmatic and preoptic) contain many melatonin receptors
Where is Melatonin secreted?
Melatonin is secreted by pineal gland once blue wavelengths of light stop stimulating the retina.
What are common sleep disorders?
