EEG, Sleep and Circadian Rhythms

Question 1

where do the active inhibitory processes that causes the brain to sleep originate from?

Answer 1

in the pons

Question 2

what area is closely associated with controlling the state of consciousness?

Answer 2

Reticular Formation of the brain stem

Question 3

what type of drugs inhibit sleep?

Answer 3

drugs that block serotonin formation

Question 4

where are suprachiasmatic nuclei (SCN) found?

Answer 4

in the hypothalmus

Question 5

what is evidence show that SCN has a role in sleep?

Answer 5

Electrical stimulation of the SCN can promote sleep and damage to the SCN disrupts the sleep-wake cycle

Question 6

what excitatory neurotransmitter does the hypothalamus release that is required for wakefulness?

Answer 6

orexin (aka hypocretin)

Question 7

what does defective orexin signalling cause?

Answer 7

narcolepsy; individual will suddenly fall asleep, sometimes even when talking.

Question 8

describe the positive feedback that allows sustained wakefulness?

Answer 8

Excitatory neurons are released from inhibition from Sleep Centres in Reticular Formation.
Stimulate excitatory pathways (both the CNS and PNS)
this loop carries on

Question 9

what occurs when these active cell become fatigued and excitatory signals fade?

Answer 9

inhibitory, peptide signals from the Sleep Centres in the Reticular Formation likely take over and rapidly inhibit the weakening excitatory signals leading to rapid progression into the sleep state

Question 10

what does assessing level of consciousness in an awake person involve?

Answer 10

• Look at their behaviour, general alertness etc

- Record patterns of brain activity using ElectroEncepheloGram (EEG)

Question 11

what are EEG waves analysed by?

Answer 11

Amplitude: the size of the wave (ranges from 0-200 µV)
Frequency: number of waves per second (ranges from 1-50+)

Question 12

does the EEG frequency increase or decrease when asleep vs awake

Answer 12

In general frequency increases with neuronal excitation so higher frequency when awake, and higher still when focused

Question 13

what is EEG characterised by when in a relaxed awake state?

Answer 13

high frequency, high amplitude waves termed alpha waves.

Question 14

what is EEG characterised by when in an alert awake state?

Answer 14

even higher frequency, low amplitude asynchronous waves termed beta waves

Question 15

why is the amplitude lower during the alert awake phase?

Answer 15

increase in activity is asynchronous as brain is doing so many things at once, and opposing polarities of the signals cancel each other out and do not get recorded on EEG.

Question 16

what are theta waves characterised by?

Answer 16

low frequency waves which can vary enormously in amplitude.

common during emotional stress

Question 17

what are delta waves characterised by?

Answer 17

very low frequency but high amplitude. They occur in deep sleep

Question 18

describe the 1st stage of sleep

Answer 18

Slow wave, non-REM, S-sleep. Slow eye movements. Light sleep. Easily roused. High amplitude, low frequency theta waves

Question 19

describe the 2nd stage of sleep

Answer 19

Eye movements stop. Frequency slows further but EEG shows bursts of rapid waves called “sleep spindles” (clusters of rhythmic waves, ~12-14Hz)

Question 20

describe the 3rd stage of sleep

Answer 20

High amplitude, very slow (2Hz) delta waves interspersed with short episodes of faster waves, spindle activity declines.

Question 21

describe the 4th stage of sleep

Answer 21

exclusively delta waves.

Question 22

describe the REM stage of sleep

Answer 22

during which there are rapid eye movements. Aka paradoxical sleep. Dreams occur during REM sleep. 25% of sleep is REM.

Question 23

which stages are known as the deep sleep?

Answer 23

stages 3 and 4

Sleep walking/talking occurs during these

Question 24

what characterises stages 1-4?

Answer 24

slow wave sleep

Question 25

what characterises REM sleep?

Answer 25

fast waves, eerily similar to those of the awake state

Question 26

what are the Physiological Characteristics of Deep, Slow Wave Sleep?

Answer 26

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

Question 27

what are the Physiological Characteristics of REM Sleep?

Answer 27

Lasts 5-30mins every 90mins Dreams mostly occur here Eye muscles show bursts of rapid activity. Profound inhibition of all other skeletal muscles HR/RR become irregular and brain metabolism increases difficult to arouse an individual from REM sleep

Question 28

what drugs increase time spent in REM sleep?

Answer 28

Anticholinesterases

Question 29

what do Sleep deprived subjects demonstrate, without exception?

Answer 29

``` Impairment of cognitive function Impairment of physical performance Sluggishness Irritability (Psychosis) ```

Question 30

what does sleep support?

Answer 30

``` Neuronal plasticity Learning and memory Cognition Clearance of waste products from CNS Conservation of whole body energy Immune function (reason sleep increases when ill?) ```

Question 31

what is the definition of insomnia?

Answer 31

“chronic inability to obtain the necessary amount or quality of sleep to maintain adequate daytime behaviour”, very subjective, very common chronic vs temporary associated with PTSD

Question 32

what are problems with hypnotic drugs?

Answer 32

can depress REM sleep addictive cause many problems on withdrawal should not be given chronically.

Question 33

what is the definition of night terrors?

Answer 33

occur in deep, delta sleep and are common in children 3-8 years, typically occurring early in the night. Children thrash and scream and may sit or stand up with their eyes open but are not properly awake and often fail to recognise their parents. The child does not remember the episode on waking the following morning.

Question 34

what is the definition of Somnambulism (Sleep-walking)?

Answer 34

occurs exclusively in non-REM sleep, mainly in Stage 4 sleep and is more common in children and young adults Somnambulists walk with their eyes open, can see and will avoid objects, can carry out reasonably complex task such as prepare food and will often obey instructions but have no recall of the episode when woken.

Question 35

what is the definition of Narcolepsy?

Answer 35

Patients enter directly into REM sleep with little warning. Effectively symptoms could be interpreted as intrusion of REM sleep characteristics onto the waking state. Very dangerous because of accident risk if e.g. driving.

Question 36

sleep is part of the circadian rhythm, what does this mean?

Answer 36

biological systems show oscillations with a 24 hour period.

Question 37

where is the “master-clock” located?

Answer 37

suprachiasmatic nucleus (SCN) of the hypothalamus, lying just above the optic chiasma.

Question 38

describe the neurones of the "master-clock'

Answer 38

These neurons have an inherent 24 hour cycle which is entrained by external cues such as light/dark cycles