Sleep Physiology

Question 1

What is the sleep?

Answer 1

Normal, recurring reversible state = loss of ability to respond to external environment, not fully aware of self and environment but can respond when stimulated

Question 2

What are some features of non-REM sleep?

Answer 2

More non-REM sleep at start of the night, synchronised rhythmic EEG activity, partial muscle relaxation, reduced cerebral blood flow, reduced heart rate and BP, some non-narrative images

Question 3

What are some features of REM sleep?

Answer 3

Mostly at end of night, EEG shows fast activity, fMRI shows increased brain activity, atonic muscles, cerebral blood flow increased, impaired thermal regulation, narrative dreaming

Question 4

What are some features of deep sleep?

Answer 4

Essential sleep = only part of lost sleep regained after sleep loss, allows cortex to recover after busy day

Question 5

Is REM classed as true sleep?

Answer 5

No = actually a form of non-wakefulness, mainly for early brain development, likely dispensable

Question 6

What drug class suppress REM sleep with no effect?

Answer 6

Tricyclic antidepressants

Question 7

How does sleep change throughout childhood?

Answer 7

Neonates = spend 16hrs per day asleep, 50% REM sleep, shorter cycles
During 1st decade percentage REM sleep falls and REM latency increases

Question 8

What are some features of sleep in the elderly?

Answer 8

Increased awakenings

Reduced REM latency, total sleep time and daytime napping

Question 9

What are the three critical processes involved in sleep onset?

Answer 9

Homeostatic response, emotional response and circadian rhythm = biology and physiology control sleep

Question 10

What is circadian rhythm important for?

Answer 10

Sleep-wake cycle, appetite and hormone secretion

Question 11

How does timing of sleep onset change with age?

Answer 11

Children sleep earlier and waken earlier, adolescents have delayed sleep pattern, elderly have an advanced sleep pattern

Question 12

How long does circadian rhythm normally last for?

Answer 12

25 hours

Question 13

What controls the body’s internal clock?

Answer 13

Light = uses retinal ganglion cells projecting to suprachiasmatic nucleus = non-rod, non-cone cells

Question 14

How does sleep help exercise?

Answer 14

No evidence of muscle recovery during sleep but does help with tissue repair
Growth hormone release is sleep related
Cell division and skin mitosis peaks during sleep

Question 15

When can the cortex rest?

Answer 15

Can only rest during sleep = can’t fully rest when awake as stays in quiet readiness

Question 16

What effect does the number of function a cortex perform have on how much sleep it requires?

Answer 16

More complicated cortices require more sleep

Question 17

What effect does lack of sleep have on the brain?

Answer 17

Most effects are prefrontal = no psychoses but become irritable and suspicious, visual illusions, microsleeps and concentration lapses also occur

Question 18

What is the function of the prefrontal cortex?

Answer 18

Doesn’t effect old and well-rehearsed tasks
Routine behaviour and logic tasks
Impairs alertness

Question 19

How does a normal brain deal with dangerous situations?

Answer 19

Understanding complex situations and ignoring irrelevancies
Assessing risks and consequences
Communicating well, and showing lateral thought and innovation

Question 20

What happens when rats are sleep derived?

Answer 20

Die within 20 days = cause not clear, become lethargic, lose weight despite eating more, develop skin ulceration and injury, no physical cause of death

Question 21

How does sleep deprivation lead to RTAs?

Answer 21

About 10% of RTAs are sleep related = most are acutely sleep deprived
truck driver falling asleep is most likely cause of accidental death at work

Question 22

How much sleep is needed for normal function?

Answer 22

Most studies suggest 7-7.5 hours a night is acceptable

Question 23

How effective is it to take a nap during the day?

Answer 23

A mid-afternoon nap of 15mins is equivalent to 90mins overnight

Question 24

What are some examples of non-REM parasomnias?

Answer 24

Non-dreaming, confusional arousals, sleep walking, sleep paralysis, bruxism, restless legs and PLMS

Question 25

What are some features of REM parasomnias?

Answer 25

Often seen preceding Parkinson’s disease
Usually later third of night
Much simpler behaviour with dreaming

Question 26

What is the epidemiology of narcolepsy?

Answer 26

Two peaks of incidence = age 15 and 36

Equal sex distribution

Question 27

What features characterise narcolepsy?

Answer 27

Daytime sleepiness, cataplexy, sleep paralysis and RBD

Question 28

What is daytime sleepiness?

Answer 28

Involuntary somnolence during eating or talking

Question 29

What is cataplexy?

Answer 29

Loss of muscle tone = triggered by emotion, occurs in 70% of patients

Question 30

How long does it take to diagnose narcolepsy?

Answer 30

Typical 10 year delay between onset and diagnosis

50% of adults report symptoms beginning as teenager

Question 31

What investigations can be done for narcolepsy?

Answer 31

Overnight polysomnography, multiple sleep latency test, lumbar puncture

Question 32

How is a multiple sleep latency test carried out?

Answer 32

Four 25 minute naps scheduled 2 hours apart
record EEG, muscle activity and eye movement
Measures time from start of daytime nap to first signs of sleep

Question 33

What is the lumbar puncture result of a patient with narcolepsy?

Answer 33

Low CSF hypocretin levels = <110 pg/ml

Question 34

What impact does narcolepsy have on driving?

Answer 34

Must stop driving cars until controlled

Permanent exclusion from driving group 2 vehicles

Question 35

What is insomnia?

Answer 35

Psychophysiological concept = alertness around sleep