EEG, Sleep and Circadian Rhythms

Question 1

Define sleep

Answer 1

State of unconsciousness from which an individual can be aroused by normal stimuli, light, touch, sound etc. and is cyclical

Question 2

How does sleep occur?

Answer 2

Due to active inhibitory processes that originate in the Reticular Formation of the brain stem (pons)

Question 3

What is the reticular formation?

Answer 3

Closely associated with controlling the state of consciousness. It sends projections to the thalamus and higher cortical areas.

Question 4

Why is it thought that serotonin is critical to sleep induction?

Answer 4

As many neurones with the reticular formation are serotonergic.

Drugs that block serotonin formation inhibit sleep.

Serotonin is a precursor of melatonin –> its release corresponds with sleep cycle (greater when falling asleep and less in the morning)

Question 5

What is the suprachiasmatic nuclei (SCN)?

Answer 5

Nerve cells of the hypothalamus which are important in the induction of sleep and the 24hr circadian rhythm

Question 6

What does damage to the SCN cause?

Answer 6

Damage to the SCN will disrupt the sleep-wake cycle

Question 7

How does the SCN induce sleep?

Answer 7

Electrical stimulation can promotor sleep –> activity of SCN stimulates release of melatonin from the pineal gland (feeling of sleepiness in humans)

Question 8

What is orexin?

Answer 8

Excitatory neurotransmitter released from the hypothalamus (only active during waking state and stop firing during sleep)

Question 9

What does defective orexin signalling cause?

Answer 9

Narcolepsy - individual will suddenly fall asleep, sometimes even when walking

Question 10

Describe induction of sleep through to wakefulness

Answer 10

Melatonin of the SCN and orexin induce sleep. When these active cells become fatigued and excitatory signals fade, inhibitory peptide signals from the reticular formation lead to progression into sleep state

Opposite happens during waking

Question 11

What are two ways to assess consciousness levels?

Answer 11

1. Look at their behaviour, general alertness, speech patterns, speech content, reading, writing and calculating skills.
2. Record pattern of brain activity using electroencephalogram (EEG)

Question 12

What is an electroencephalogram (EEG)?

Answer 12

EEG uses electrodes placed on the scalp to record activity of underlying neurones

Recording shows wave patterns that reflect electrical activity of the brain

Question 13

How are wave recordings analysed on EEGs?

Answer 13

By amplitude and frequency

Question 14

How does amplitude and wavelength change with decreasing frequency?

Answer 14

Wavelength increases and frequency decreases

Question 15

What are the four main types of wave patterns found on EEGs?

Answer 15

1. Alpha
2. Beta
3. Theta
4. Delta

Question 16

What waves are present during the relaxed, awake state?

Answer 16

High frequency, high amplitude waves – alpha waves state

Question 17

What waves are present during the alert, awake state?

Answer 17

Higher frequency, low amplitude asynchronous waves – beta waves

There is low amplitude because of the brain’s high activity, it fires impulses without sequence and so the opposing polarities of the signals cancel each other out and do not get recorded on EEG.

Question 18

What are theta waves?

Answer 18

• Low frequency with varying amplitude

* Common in children and during emotional stress and frustration in adults

Question 19

What are delta waves?

Answer 19

• Low frequency, high amplitude

* Occur in deep sleep

Question 20

What are the five stages of the sleep cycle?

Answer 20

Stage 1:
• Slow wave, non-REM, s-sleep
• Slow eye movements, light sleep and easily aroused.
• High amplitude, low frequency theta waves

Stage 2:
Bursts of rapid waves called sleep spindles (clusters of higher frequency rhythmic waves)

Stage 3:
• High amplitude, very slow delta waves interspersed with short episodes of faster waves
• Spindle activity declines

Stage 4:
Exclusively delta waves

Difficult to rouse from stage 3 and 4 sleep – deep sleep – and sleep walking/talking occurs during these stages

Stage 5:
• Rapid Eye Movements (REM) aka paradoxical sleep
• Dreams occur during REM sleep

Question 21

What are physiological characteristic of deep, slow wave sleep?

Answer 21

• Deep sleep that occurs in the first hours of sleep
• Most restful type of sleep
• Association with decreased vascular tone (and therefore BP), respiratory and basal metabolic rate (hence drop in BT)
• Dreams may occur but are rarely remembered

Question 22

Describe paradoxical sleep

Answer 22

Following initial S-wave sleep of stages 3 and 4, there is a gradual awakening towards Stage 1, but not like the initial Stage 1, instead REM sleep during which EEG waves are desynchronized, high frequency, low amplitude, very like the awake state

Question 23

What are the physiological characteristics of REM sleep?

Answer 23

Lasts 5-30mins every 90mins or so during normal nights sleep
• Dreams mostly occur
• Eye muscles show bursts of rapid activity
• Profound inhibition of all other skeletal muscles (other than eyes) due to inhibitory projection from pons to spinal cord – prevents acting out of dreams
• Dependent on cholinergic pathway within the reticular formation and their projection to the thalamus, hypothalamus and cortex
• HR/RR become irregular and brain metabolism increases.
• Very difficult to arouse from REM sleep, although might awaken spontaneously

Question 24

What are four outcomes of sleep deprivation?

Answer 24

• Impairment of cognitive function
• Impairment of physical performance
• Sluggishness
• Irritability

Question 25

What six functions does sleep support?

Answer 25

• Neuronal plasticity
• Learning and memory
• Cognition
• Clearance of waste product from CNS
• Conservation of whole body energy (however, cerebral O2 consumption increases in REM sleep)
• Immune function

Question 26

How does sleep change over a lifetime?

Answer 26

Total sleep decreases rapidly through childhood and adolescence. Percentage of REM sleep also declines:

• 80% in 10week premature infant
• 50% at full term
• 25% in adulthood
• May be absent in 80+ yrs old

Total time asleep is greatest during development when brain is maturating and synaptic formation is occurring rapidly.

Question 27

What is insomnia?

Answer 27

Chronic inability to obtain the necessary amount of quality sleep to maintain adequate daytime behaviour

Question 28

What are two types of insomnia?

Answer 28

• Chronic, primary insomnia where there is usually no identifiable psychological or physical cause
• Temporary, secondary insomnia in response to pain, bereavement or other crisis

Question 29

What are two drugs which treat insomnia?

Answer 29

• Barbituates (side effects on REM sleep)

* Benzodiazepines (addictive)

Question 30

In what stage of sleep do nightmares occur?

Answer 30

REM sleep

Question 31

In what stage of sleep do night terrors occur?

Answer 31

Deep, delta sleep and are common in children 3-8yrs, usually early in the night

Question 32

What is somnambulism?

Answer 32

Sleep walking

Question 33

In what stage of sleep does somnambulism occur?

Answer 33

Exclusively in non-REM sleep, mainly stage 4 and more common in children, probably due to decline in stage 4 in adults

Question 34

Describe somnambulism

Answer 34

They walk with their eyes open, can see and will avoid objects and will often obey instruction but have not recall of the episode when woken

Question 35

Describe narcolepsy

Answer 35

Patients enter directly into REM sleep with little warning. Symptoms could be interpreted as intrusion of REM sleep characteristics onto the waking state

Linked to dysfunctional orexin release from the hypothalamus

Question 36

What is the primary clock for circadian rhythm?

Answer 36

Suprachiasmatic nucleus (SCN) of the hypothalamus

These neurons have an inherent 24hr cycle which is entrained by external cues such as light/dark cycles (cant be only one because blind people have circadian rhythm)