L2 Neural Basis of Sleep

Question 1

How is sleep measured?

Answer 1

Polysomnography:
EEG (electroencephalography)
EOG (electrooculography; eye movements)
EMG (electromyography; muscle activity)

Question 2

What are the different frequencies of EEG?

Answer 2

Beta > 13 Hz - amplitude of < 5 mV
Alpha 8-13 Hz - amplitude of 5-15 mV
Theta 4-7 Hz - amplitude of 10-50 mV
Delta < 4 Hz - amplitude of > 50 mV

Question 3

What happens in stage 1 sleep?

Answer 3

Takes up 4-5% of a night’s sleep
Theta activity is observed
There is a drop in HR, breathing and body temperature
Muscles will start to relax

Question 4

What happens in stage 2 sleep?

Answer 4

Takes up 45-55% of a night’s sleep
Start to see sleep spindles (rapid bursts of activity from the thalamus projecting to cortical regions of brain - maybe to do with memory consolidation)
Can also see k-complexes, present as your body is trying to prevent external stimuli from waking you up; helping with the gradual transition

Question 5

What happens in stages 3 and 4?

Answer 5

Takes up 4-6% and 12-15%
SWS, enters delta wave activity, involves a group of neurons firing at the same time which is why there is the large burst in activity
If wake up in this stage will feel tired
Night terrors in young children common in this stage
Heavily researched in relation to memory consolidation

Question 6

What happens in REM sleep?

Answer 6

Theta and beta activity, increased EOG activity, muscle atonia, dreams and nightmares (increased REM % in PTSD, Pase-Schott et al., 2015)
Suggested to be involved in emotional regulation
Occurs in later half of the night
More likely to wake up in this stage but unlikely to remember it

Question 7

How can we view sleep stages?

Answer 7

In a hypnogram,

For about 8 hours of sleep you would usually see around 5 cycles (one every 90 minutes)

Question 8

How do we know when to sleep?

Answer 8

Circadian Rhythms
Functions of living organisms that display a rhythm of about 24 hours
Diurnal = active during the day
Nocturnal = active during the night

Question 9

What is the biological body clock?

Answer 9

The suprachiasmatic nucleus, just past where the optic nerve crosses
All SCN cells have a 24 hour rhythm and we have these cells in different structures of the body e.g. hormone secretion, appetite control
All managed by the master body clock
It is in charge of timing not the functions themselves (Moore, 2007)

Question 10

What happens if you remove or damage the SCN?

Answer 10

Animal’s sleep patterns are all over the place and lose these 24 hour patterns

Question 11

What do we need to reset the SCN?

Answer 11

Light (the main zeitgeber)

Jet lag is because the SCN is out of sync with the changed environment

Question 12

How do blind people have 24 hour rhythms?

Answer 12

Often individuals are blind due to rod or cone damage but they can still process light due to the photosensitive retinal ganglion cells which are sensitive to blue light
Otherwise they would be living in a constant state of jet lag

Question 13

Why are retinal ganglion cells sensitive to blue light?

Answer 13

Due to a photosensitive pigment called melanopsin which is activated by blue light

Question 14

What is sleep homeostasis?

Answer 14

Or sleep pressure

A need to sleep which increases throughout the day

Question 15

How does the CR change throughout the day?

Answer 15

It is slow in the morning and increases throughout the day due to alertness and dips again in the evening

Question 16

How does sleep homeostasis change throughout the day?

Answer 16

Starts low and increases throughout the day as you get more tired
Need this signal to be greater than alertness to initiate sleep
When sleep is initiated, sleep pressure decreases and resets itself

Question 17

Why does sleep pressure increase?

Answer 17

Due to a build up of adenosine, a by-product of ATP, which is used throughout the day

Question 18

What happens in the evening in regards to hormone secretion?

Answer 18

Melatonin is secreted in the pineal gland when its dark, as these levels increase so does the need to sleep.
Light blocks melatonin release, interacting with the circadian rhythm
Melatonin release inhibits the SCN

Question 19

What are the 8 neurotransmitters involved in sleep regulation?

Answer 19

Excitatory:
Noradrenaline
Histamine
Dopamine
Acetylcholine
Serotonin

Neuro-modulatory:
Hypocretin (orexin)

Inhibitory:
GABA
Galanin

Question 20

What are the neurotransmitters involved in the ascending arousal system?

Answer 20

Also known as the reticular activating system
Noradrenaline, serotonin, histamine, acetylcholine, dopamine and orexin innervate the cortical regions to keep you awake
They inhibit sleep-active NTs such as GABA and Galanin

Question 21

Which regions are critical for regulating arousal?

Answer 21

The basal forebrain and pons region - the structures inside these areas are important for this process

Question 22

Where does acetylcholine project to?

Answer 22

From the LDT and PPT to the thalamus

Question 23

What is hypocretin’s role in the ascending arousal system?

Answer 23

It is a neuro-modulator which involved in flipping the sleep/wake switch
Individuals with narcolepsy have a depletion in hypocretin which is why they can’t stabilise their pattern

Question 24

What is the sleep pathway?

Answer 24

The VLPO is the key area for inhibitory NTs (GABA and Galanin)
When these are active they inhibit all the excitatory NTs
The build up of adenosine also blocks hypocretin so it can no longer modulate the wake-promoting NTs
The activity of these excitatory NTs decreases so much that it releases their inhibition of sleep active inhibitory NTs

Question 25

How is the waking state maintained?

Answer 25

By input from the brainstem reticular formation which is distributed widely over the cortex and forebrain

Question 26

What are the 2 patterns of projection of the brainstem reticular formation to the cortex?

Answer 26

1. Direct projections from the brainstem to the basal forebrain and cerebral cortex - include projections from serotonin neurons in the midbrain raphe, noradrenaline neurons of the LC and DA neurons of the substantia nigra and VTA
2. Projections to the diencephalic and basal forebrain areas that then project to the cortex

Question 27

What happens with VLPO damage?

Answer 27

Results in a syndrome of prolonged wakefulness

Question 28

What are the implications of naps?

Answer 28

That SCN only has gentle control over the sleep-wake cycle due to the fact that we can take naps during the day and also stay up at night

Question 29

What are the 2 models developed to explain how the pacemaker influences the 24 hour patterns?

Answer 29

1. The opponent processes model - increasing need for sleep during the day is counteracted by a circadian process that increasingly stimulates wakefulness
2. The two-process model - provides a mathematical translation of this concept. Considers the alternation of wakefulness and sleep to result from sleep need (process S) and circadian processes (process S)

Question 30

What are evaluations of these two models?

Answer 30

They are simplifications of reality but this is mostly unavoidable due to real life situations being so complex and there being so many individual differences
Do help to understand the major principles of regulation - but other major principles may be overlooked
Occurrence of short awakenings cannot be understood with these models