Sleep Physiology, Hypersomnolence and Parasomnias

Question 1

What is sleep?

Answer 1

Normal, recurring, reversible state

There is a loss of ability to respond to the external environment

It is intermediate between consciousness and unconsciousness:
• Not conscious as they are not fully aware of self and the environment
• Not unconscious as they can respond when stimulated

Question 2

2 broad categories of sleep?

Answer 2

Non-REM sleep - occurs mainly at the start of the night and comprises 3/4 of sleep for young adults; responsible for non-narrative image dreams that elicit strong emotional responses

REM sleep - occurs mostly at the end of the night; responsible for narrative dreams (following a story / film-like)

NOTE - both sleep states have dreams

Question 3

EEG findings and physiological features of non-REM sleep?

Answer 3

Synchronised, rhythmic EEG activity

There is:
• Partial relaxation of muscles
• Reduced cerebral blood flow
• Reduced HR, BP and tidal volumes

Question 4

EEG and fMRI findings and physiological features of REM sleep?

Answer 4

EEG shows fast activity
fMRI shows increased brain activity
NOTE - this is similar to the state of wakefulness, i.e: comparable to being awake

There is:
• ATONIA of muscles (EXCEPT diaphragm and extraocular muscles)
• Increased cerebral blood flow
• Impaired thermal regulation

Question 5

Which type of sleep is more important?

Answer 5

Deep, non-REM sleep, where the body enters a profound state of relaxation, is the most important; this is proven by the following findings:
• When sleep is lost, the only part that is regained during next sleep is deep, non-REM sleep
• Deep, non-REM sleep allows the cortex to recover after a busy day

Question 6

If non-REM sleep is more important, what is the purpose of REM sleep?

Answer 6

Mainly for early brain development in infancy; postulated that this is an evolutionary advantage as it provides substitute stimulation for wakefulness

It is however dispensable in others, e.g: dolphins do not have REM sleep and tricyclic drugs suppress REM sleep with no adverse effect

Question 7

Proportion of neonatal sleep that is REM? How does this change throughout life?

Answer 7

Neonates spend 16 hours per day asleep; 50% of this is REM sleep

During the 1st decade, % of REM sleep decreases, REM latency increases

Question 8

Sleep in the elderly?

Answer 8

Increased awakenings

Reduced REM latency and total sleep time

Day time napping

Question 9

Can a person resist falling asleep?

Answer 9

If the body wants you to fall asleep, you will fall asleep, regardless of time, environment, consequences

This is the reason for RTAs, due to sleeping at the wheel; 10% of RTAs are sleep-related

Question 10

What factors control sleep?

Answer 10

Biology and physiology but NOT psychology

Question 11

Importance of circadian rhythm?

Answer 11

AKA body clock

Many processes are controlled by an endogenous factor; Important for sleep-wake cycle, appetite, body temperature, alertness and hormone secretion

Question 12

Changes in circadian rhythm with age?

Answer 12

Timing changes with age:
• Children sleep earlier and awaken earlier
• Adolescents sleep later and awaken later, i.e: delayed sleep pattern
• Elderly have an advanced sleep pattern

Question 13

Phenomena that occur during non-REM sleep?

Answer 13

Protein synthesis

Cell division and growth

Question 14

Phenomena that occur during REM sleep?

Answer 14

Consolidate memory and possibly delete unnecessary memory

Maintains immunocompetence

Perhaps important in conserving energy, as species with high metabolic rates have longer sleep times

Question 15

Peaks of sleepiness in a typical circadian rhythm?

Answer 15

3-4 am

2-3 pm

Question 16

Length of the normal circadian rhythm?

Answer 16

Last around 25 hours; recent studies suggest it may be closer to 24 hours and 20 minutes

NOTE - regardless of the study, normal circadian rhythm is >24 hours

Question 17

How is the circadian rhythm / body clock trained?

Answer 17

Circadian rhythm is reset everyday:
• Non-rod, non-cone cells detect LIGHT and projectthis info to the suprachiasmatic nucleus
• Routine of eating breakfast, putting on clothes, etc

Question 18

Examples of when changes in light can cause issues with circadian rhythm?

Answer 18

International Space Station - experience several periods of daylight and darkness everyday

Arctic research centre - exposed to no light

Question 19

How does sleep deprivation affect exercise?

Answer 19

No evidence of muscle recovery during sleep; however, sleep does help with tissue repair

Question 20

Processes that occur during sleep?

Answer 20

Sleep-related GH release

Cell division peaks during sleep:
• Skin mitosis peaks during sleep

Question 21

Why must the brain sleep?

Answer 21

Cortex cannot fully rest during sleep and more complicated cortices require more sleep

Question 22

Signs of sleep deprivation?

Answer 22

Most are pre-frontal:
• Irritable and suspicious (not psychoses)
• Visual illusions
• Microsleeps and concentration lapses 
• Impaired alertness 

However, sleep deprivation does not affect:
• Old and well-rehearsed tasks
• Routine behaviour
• Logic tasks

Question 23

Examples of dangerous errors that can be made when sleep deprived?

Answer 23

Inability to understand complex situations and ignoring any irrelevancies

Difficulty assessing risks and consequences

Inability to deal with the unexpected

Tracking events and updating strategies becomes difficult

Communication skills are impaired

No ability to think laterally or innovate

Question 24

Does sleep deprivation kill humans?

Answer 24

Do not know but likely does (rats die within 20 days although the cause of death is unclear, as there is no physical cause)

Question 25

Acceptable sleep length?

Answer 25

Most studies suggest that 7-7.5 hours is acceptable 4 hours is not

Question 26

Benefits of a nap?

Answer 26

Mid afternoon nap of 15 minutes is equivalent to 90 minutes overnight It should not be >15 minutes, as this ceases being a nap and becomes sleep (wake feeling worse)

Question 27

What is parasomnia?

Answer 27

Group of sleep disorders that inv. unwanted events or experiences that occur while falling asleep, sleeping or waking up May include abnormal movements, behaviors, emotions, perceptions or dreams NOTE - brain does not wake or fall asleep instantly; it is a slow process and different regions take different times to leave wake / sleep

Question 28

Types of non-REM parasomnia?

Answer 28

Non-dreaming Confusional arousals Sleep walking Sleep terrors and paralysis Bruxism (involuntary, habitual grinding of teeth during sleep) Restless legs and PLMS NOTE - patients often display complex behaviours

Question 29

Types of REM parasomnia?

Answer 29

Involve dreams and much simpler behaviour Usually occur during the latter 1/3rd of the night

Question 30

Occurrence of REM parasomnia?

Answer 30

Often precede Parkinson's disease diagnosis (REM sleep behaviour disorder)

Question 31

What is narcolepsy?

Answer 31

Long-term neurological disorder that involves a decreased ability to regulate sleep-wake cycles

Question 32

Occurrence of narcolepsy?

Answer 32

Rare There is no gender preponderance Age of onset is variable but there are 2 peaks: • 15 years • 36 years Many patients with REM sleep behaviour disorder (RBD) have narcolepsy

Question 33

Symptoms and signs of narcolepsy?

Answer 33

``` Daytime sleepiness (may be severe and impossible to resist): • Involuntary somnolence during eating / talking ``` Cataplexy ('to strike down with fear') is a loss of muscle tone that is triggered by emotion (happiness, anger, fear, etc); it is present in 70% of patients Hypnagogic hallucinations occur at sleep onset Sleep paralysis is the inability to move upon falling asleep or awakening with retained consciousness

Question 34

When do symptoms of narcolepsy begin?

Answer 34

50% of adults report symptoms beginning as a teenager; this can lead to impaired social and academic performance

Question 35

Ix for sleep disorders?

Answer 35

Overnight polysomnography Multiple Sleep Latency Test Lumbar puncture for CSF hypocretin levels: • LOW CSF HYPOCRETIN levels (<110 pg/ml or 1/3rd of the mean control value) are consistent with NARCOLEPSY

Question 36

Procedure of the multiple sleep latency test?

Answer 36

4 x 25 minutes naps are scheduled about 2 hours apart Record: • EEG • Muscle activity • Eye movement Time is measured from the start of the daytime nap to the 1st signs of sleep (sleep latency); patient falls asleep faster if they are sleepier

Question 37

Consequences of narcolepsy?

Answer 37

Social embarrassment and source of humour Job impaired due to sleep attacks and memory problems Increased risk of death for automobile accidents

Question 38

Rules for driving with narcolepsy?

Answer 38

Cease driving on diagnosis, until control is achieved Permanent exclusion from group 2 drivers