Psychophysiology of sleep and impact of insomnia on health Flashcards
What is sleep?
A physical state of:
- postural recumbency
- Quiescence
- closed eyes
However, two separate states of sleep have been identified:
REM-Rapid Eye Movement
Non-REM-(4 semi-distinct sleep stages)
What are the stages of sleep?
Sleep Stage Architectural Characteristics Pattern Relaxed, Wakefulness Alpha waves are present when one begins a state of relaxation, high frequency
Stage N1
Irregular, jagged, low amplitude waves; brain activity begins to decline, decreases in frequency
Stage N2
Presence of sleep spindles and K-complexes
Stage N3 Low frequency (slow), high amplitude waves (delta waves, Slow Wave Activity - SWA)
REM
Irregular, low-amplitude and high frequency (fast) waves; PGO waves; rolling eye movements; loss of muscle tone
What are the specifics of stage 2 sleep?
NREM takes up 75% of the whole night and REM takes up approximately 20-25%
Stage 2 takes up between 45-55% of the whole night
What is the sleep cycle?
N1 -> N2 -> N3 -> N2 -> REM
repeats every 90 minutes
What is apparent during REM?
- muscle tension is non existent
- body paralysis
- eye movements and respiratory system active
- dream activity
What patterns do we see throughout the night?
N3 reduces, REM increases
?What areas of the brain are active/inactive during sleep
Prefrontal Cortex – inactive throughout sleep
Memory (STM - short term memory)
Attention
Perception
Limbic Cortex – Inactive NREM, active during REM
Autonomic Function
Parietal Cortex – Less active REM, down regulated
- emotions
Frontal Cortex – less active NREM
Describe the Ascending Reticulr Activating System (ARAS) and what happens when there are problems with any areas?
A heterogeneous region of several brain areas that runs…
through brainstem from the medulla
to the pons and midbrain
and into the posterior hypothalamus
Experimental lesions in animals and clinical observations in patients with strokes/tumours produce hypersomnolence
Electrical stimulation of this area causes aroused EEG and behavioural activation
Confirms the reticular formation is necessary for wakefulness
problems with this are associated with increased wakefulness
What do the neurons of the ARAS produce and what are their roles?
Neurons of the ARAS produce neurotransmitters with 2 effects:
- Excitatory effects on target neurons throughout the cortex to promote arousal
- Acetylcholine (Ach)
Norepinephrine (NE)
Dopamine (DA)
Serotonin (5-HT)
Histamine (HA)
Orexin/hypocretin - Inhibitory effects on target neurons, promotes sleep by reducing activity of wak-promoting neurons:
γ-aminobutyric acid (GABA)
What are the regulators of sleep?
suprachiasmatic nucleus - regulates circadian rhythm and produces 2 hormones:
- melatonin - tells body it is night time
- cortisol - tells body it is day time
- Core body temperature
Describe the hormones of the endocrine system during sleep.
PITUITARY GLAND:
- GH - anabolic hormone that regulates body composition, reaparative hormone which reduces oxidative stress and repairs damage to tissue, important in N3
- PRL - stimulates lactation in women, pleiotropic actions (slow wave sleep)
- ACTH - reduces in slow wave sleep, stimulates release of cortisol from adrenal cortex
- TSH - stimulates release of thyroid hormones from thyroid gland, reduces
- LH - stimulates ovarian and testicular function, increases
- FSH - stimulates ovarian and testicular function, increases
Adrenal cortex:
Cortisol - stress hormone, antiinsulin effects, reduces during N3
Gonads: Testosterone - stimulates spermatogenesis
Ovaries: Estradiol - stimulates follicular growth
Pancreas: Insulin - regulates blood glucose levels
Pineal gland - melatonin - hormone of the dark that transmits information about the dark-light cycle
Adipose tissue - leptin - satiety hormone regulating energy balance
Stomach: Ghrelin - hunger hormone regulating energy balance
How does sleep clean the brain of toxins?
…brain cells shrink during sleep to open up the gaps between neurons and allow fluid to wash the brain clean.
“The brain only has limited energy at its disposal and it appears that it must choose between two different functional states - awake and aware or asleep and cleaning up,” said researcher Dr Maiken Nedergaard.
“You can think of it like having a house party. You can either entertain the guests or clean up the house, but you can’t really do both at the same time.“
Their findings build on last year’s discovery of the brain’s own network of plumbing pipes - known as the glymphatic system - which carry waste material out of the brain.
Scientists, who imaged the brains of mice, showed that the glymphatic system became 10-times more active when the mice were asleep.
Describe how the circadian rhythm works.
You have your endogenous cues:
- CBT
- Chronbiological changes
- endocrine changes
And exogenous cues - Zeitgebers which help regulate light and dark cycles
When it is light, retina transmits signals via optic nerve to the SCN which inhibits melatonin production
When it is dark, retina transmits signals along optic nerve to SCN to increase melatonin production
- peripheral oscillators also play a role
What are the different circadian periods -
24 - 25 hours - Range observed in free-running blind human subjects (Robilliard et al, 2002)
24.25 hours - Average period in humans (forced desynchrony protocol)
(Czeisler et al, 1999)
23.25 hours - Advanced sleep phase syndrome
patient (Jones et al, 1999)
What is the Two-Process Model of Sleep?
Model proposed by Borbély (1982) describes 2 drives for sleep:
Homeostatic (process ‘S’)
Circadian (C)
Homeostatic influence results from accumulation of “some substance (S)” during prolonged wakefulness
During prolonged wakefulness, energy producing brain systems run down
