EEG & Sleep

Question 1

Define Sleep

Answer 1

A cyclical state of consciousness from which an individual can be roused by normal stimuli such as light, sound, touch.

Question 2

What neural pathways are involved in the sleep/wake process?

Answer 2

• Seratogenic sleep centres in the Pons
• Other sleep inducing peptides found in CSF
• Melatonin release triggered by the Suprachiasmaticnuclei of the hypothalamus
• Excitatory orexin neurons in hypothalamus

Question 3

How do seratogenic sleep centres in the pons affect sleep?

Answer 3

• Recticular Formation in the Pons
• Contains seratonin releasing neurons

We know this is involved in sleep as destroying it or blocking seratonin prevents sleep

Question 4

How is the hypothalamus involved in inducing sleep?

Answer 4

• Suprachiasmaticnuclei in Hypothalamus
• SCN activity leads to melatonin release from pineal gland –> Corresponds with sleepiness

We know that electrically stimulating the SCN induces sleep and damages it disrupts sleep-wake cycle

Question 5

How is the hypothalamus involved in wakefullness?

Answer 5

Excitatory neurons in the hypothalamus release Orexin (hypocretin) during waking, this maintains wakefullness.
They stop during sleep

Question 6

Describe how the sleep wake cycle occurs:

Answer 6

Excitatory neurons (in Ascending Reticular Activating System) overtake inhibitory cells

• -> Stimulates excitatory pathways in CNS/PNS
• -> +ve feedback maintains wakefullness for many hours
• -> Excitatory cells fatigue & signals fade
• -> Inhibitory signals from the reticular formation sleep centres overtake the excitatory signals
• -> Sleep
• -> Overnight the inhibitory cells fatigue, excitatory ones rest and take over again in the morning

Question 7

What would we do to assess the level of consciousness in a patient?

Answer 7

• Electroencephalogram
• Behaviourly
  Alertness = Speech content/patterns = Reading = Writing = Calculating skills = Spell/count backwards

Question 8

What does an electroencephalogram measure?

Answer 8

Electrical activity of the brain

In Amplitude and Frequency (rises with neuronal excitation)

Question 9

Sometimes brain activity is very high but the amplitude is low, why is this?

Answer 9

The brain waves are asynchronous.
This means the brain is doing lots of things at once and the opposing polarities of its signals cancel eachother out on the EEG

Question 10

What are the types of EEG wave patterns?

Answer 10

Alpha
Beta
Theta
Delta

Question 11

When do each type of EEG wave occur?

Answer 11

Alpha - Awake but relaxed
Beta - Awake and Alert
Theta - Emotional stress/frustration/sleep stage 1&2
Delta - Deep Sleep (stages 3 & 4)

Question 12

Describe the characteristics of the different EEG wave types?

Answer 12

Alpha
- High F & A

Beta

• High F
• Low A (Asynchronous)

Theta

• Low F
• Variable A

Delta

• Low F
• High A

Question 13

What are the stages of the sleep cycle?

Answer 13

Stage 1 - Slow Wave non-rem sleep (S-sleep) - Theta
Stage 2 - Theta (but even slower F)
Stage 3 - Delta Waves
Stage 4 - Delta Waves 
Stage 5 - REM Sleep (Beta Waves)

1-4 are known as slow wave sleep
REM sleep has rapid waves

Question 14

During what stages of sleep do eye movements occur?

Answer 14

Stage 1 - Slow eye movements

REM - Rapid eye movements

Question 15

Stage 2 of sleep is very low Frequency Theta waves, what else happens?

Answer 15

Bursts of rapid waves called sleep spindles

Question 16

What stages of sleep are known as deep sleep?

Answer 16

Stages 3 & 4

Question 17

Why would we call REM sleep Paradoxical sleep?

Answer 17

Because the High frequency, Low amplitude waves mimic awake/alert beta waves

Question 18

What stage of sleep are dreams remembered from?

Answer 18

REM sleep

Question 19

How does the sleep cycle change over the night?

Answer 19

As the night progresses we spend more time in REM sleep and less in Deep Sleep

Question 20

What physiological changes occur during deep sleep?

Answer 20

Its the most restful period

Decreased Vascular Tone –> Drop in BP
Drop in Respiratory & metabolic rate

Question 21

How long is a sleep cycle?

Answer 21

Roughly 90mins

Question 22

Why do our eyes move during REM sleep?

Answer 22

Because the rest of the bodies skeletal muscles are inhibited by projection from the pons to prevent you acting out your dream

Question 23

What happens if there’s dysfunction in the inhibitory projections from the Pons to the spinal cord?

Answer 23

REM Sleep Behavioural Disorder

People act out their dreams, which can be very dangerous

Question 24

What effect do anticholinesterases have on the sleep cycle?

Answer 24

They increase the time spent in REM sleep.

Because REM sleep is dependent on cholinergic pathways in the reticular formation of the pons and their projection to the thalamus, hypothalamus and cortex

Question 25

What physiological changes occur during REM sleep?

Answer 25

Heart & Resp Rate are irregular | Brain metabolism rises

Question 26

Compare the physiological characteristics of deep sleep vs REM sleep?

Answer 26

Deep Sleep: - Drop in resp rate, metabolic rate & vascular tone (Blood Pressure) REM sleep: - Irregular Heart & resp rate - Rise in brain metabolism

Question 27

What happens if your deprived of REM sleep one night?

Answer 27

The next chance you get to sleep your body undergoes a catch up stage. Indicating its very important

Question 28

What processes are supported by sleep?

Answer 28

- Cognition - Learning/memory - Neuronal Plasticity - Waste clearance from CNS - Conserving energy - Immune Function

Question 29

So what are the effects of sleep deprivation?

Answer 29

- Impaired cognitive function - Impaired physical function & Sluggishness - Irritability - ~Psychosis Also disrupts neuronal plasticity, immune function, energy levels and waste clearance

Question 30

How does sleep change throughout life?

Answer 30

Total Sleep time & REM sleep % are highest in childhood, probably due to brain development occuring. Both drop off again after ~65 yrs REM sleep can be completely absent in those >80

Question 31

How common are sleep disorders?

Answer 31

~25% of people are affected by sleep disorders at some point in their life?