Sleep and Circadian Rhythms Flashcards
What are circadian rhythms?
Circadian = ‘about a day’ The criteria is: Repeat once a day Persist in the absence of external cues Be able to be adjusted to match local time
Suggests ‘physiological clock’ (internal clock)
Normal adult human – 8 hours sleep
Examples: Urine excretion, body temperature and sleep-wake cycle
What are retinal ganglion cells used for?
Entrain to day/night cycle
Needs to detect light change
Deeper, light activates Melanopsin
What is the pathway from the retinal ganglion cells?
Retinal ganglion cells Retinohypthalamic tract Anterior hypothalmus Suprachiasmatic nucleus Paraventricular nucleus Anterior horn thoracic spinal cord Sup. Cerv. Ganglia Dorsal thalamus Pineal gland
What is the suprachiasmatic nucleus?
Sits in the hypothalamus and is responsible for circadian rhythms
What is the pineal gland?
This has different cell types such as: Pinealocytes – produce and secrete melatonin (the secretion is controlled by the SCN) Interstitial cells Perivascular phagocytes Neurones
What is melatonin?
It is derived from tryptophan, and the rate limiting step is between serotonin and N-acetylserotonin
Influences sleep-wake cycle
Not stored in cells - therefore widespread in all tissues
Secreted directly into CSF and blood
Antioxidant
Secretion increases with darkness as in the day time SCN inhibits PVN using GABA
Therefore high levels are produced in the dark
Describe sleep?
Sleep is a readily reversible state of reduced responsiveness to, and interaction with, the environment
You can delay it but not avoid it, as lack of psychological and physical effects
This is universal across all higher vertebrates and maybe all animals
1/3 of life is spent asleep - 25% of that is in an active dreaming state
It is cyclical with 4-6 REM episodes
What is the general sleep cycle?
24 hour cycle
8 hours asleep
16 hours awake – different levels of arousal/alertness/wakefulness
What are the stages of sleep?
Awake
Stage 1 - Drowsy, lower frequency and increased amplification
Stage 2 - Light, decreased frequency and spikes (sleep spindles)
Stage 3 - moderate/deep, further decrease in frequency and increased amplification
Stage 4 - Deep, delta waves 0.5-4 Hz and high amplitude
REM sleep
What is REM sleep?
EEG shows it is similar to awake state (paradoxical sleep)
Physiological functions increase almost to “awake” levels, energy consumption of brain is higher
Lower motor neurons in spinal cord are inhibited
There is paralysis of large muscle groups but muscles of eye movement & inner eye are strikingly active
Incoming sensory stimuli are blocked (they don’t reach the cortex)
Subjects spend 10 minutes in REM, before the brain goes through stages I-IV
REM decreases with age: birth - 8 hours, 20yrs - 2 hours and 70yrs - 45 mins
What is wakefulness/arousal?
Wakefulness/arousal - this stimulates the pons and midbrain junction
The neurotransmitters that help activate neural systems in waking are: Noradrenaline, serotonin (5-HT), histamine and acetylcholine
Why do we sleep?
Ecological: quiet time to avoid predation
Metabolic: reduces energy expenditure
Learning: memory consolidation or erasure
We need less sleep as we get older
We can create a “sleep debt” - but it must be repaid
What are some sleep disorders?
Sleep walking (somnambulism)
Peaks at 11 yrs, 40% will have suffered
Stage 4 non-REM sleep
Hard to wake up, slow wave sleep
Sleep talking (somniloquy)
Most people will have
Garbled and non-sensical
Sleep terrors
3-8 yrs
Not nightmares (REM)
Stage 3 & 4 non-REM
Narcolepsy
1 in 2500 in the UK
You can enter REM sleep from wakefulness and is very abrupt
Can last 30 secs to 30 mins
What is jet lag?
This alters you light/dark cycle
Your body tries to restore your pattern, but it takes a couple of days
It could be caused by gene expression changes in the SCN, as negative feedback could lead to slow adaptation
What are some outcomes of sleep deprivation?
Increased tension
Increased irritability
Depression
Confusion
