24.2 Sleep and Anaesthesia Flashcards
What are the different stages of sleep that can be seen on an EEG?
slow wave sleep (I-III) and rapid eye movement (REM) sleep
Describe the EEG during different stages of sleep.
- Wakefulness
- Low amplitude, fast waves
- Stage 1 (Non-rapid eye movement)
- Slightly larger amplitude, quite fast waves
- Slow eye movements
- Stage 2 (Non-rapid eye movement)
- Larger amplitude waves
- Includes sleep spindles (bursts of activity) and K-complexes (large waveforms) -> These are characteristic of stage 2 NREM
- Stage 3 (Non-rapid eye movement)
- High amplitude, slow waves (1-4Hz)
- REM (Rapid eye movement)
- Appears very similar to wakefulness
What can cause a variance in EEG?
Varies with age and some diseases (e.g. Schizophrenia) and neurodegenerative diseases.
What is the definition of circadian rhythms?
Physical, mental and behavioural changes that follow a 24-hour cycle - primarily in response to light and dark
What are examples of some physiological and biochemical processes that have rise and fall with daily rhythms?
- Body temp
- Blood flow
- Urine production
- Hormone levels
- Hair growth
Which hormone is the endogenous marker of the biological clock?
Melatonin
How does melatonin control the biological clock?
- Light levels affect melatonin production
- E.g. in low light: SCN in hypothalamus makes more melatonin –> make you more sleepy
- But in high light levels, less melatonin release –> more awake
Is sleep a passive or active process in the brain?
Active, as there are many neurons that fire during sleep
What are the common principles of the diffuse modulatory systems?
- Core of each system has a small set of neurons (several thousand)
- Neurons arise from central core of brain, mostly from brainstem
- Each neuron can influence many others - MANY synaptic contacts
- Transmitters released into ECF (not synaptic cleft) so can diffuse to many neurons rather than being confined
What is the origin of the neurons in the noradrenergic diffuse system?
Locus coeruleus (in pons)
What are other typical sleep changes with ageing?
- Delayed onset of sleep
- Earlier to bed, earlier to rise
- Reduced slow wave sleep (and reduced REM sleep)
- Reduced threshold for arousal from sleep
- Fragmented sleep with multiple arousals
- More daytime napping
How is sleep different between a baby and an old person? What is a possible explanation?
- Baby - can have 8 hours of REM sleep
REM sleep duration and number of times it is entered decreases with age - Old person - can have only 45 mins of REM sleep
Why?
May be reduction in need for memory consolidation
How can neurodegenerative disorders disrupt sleep?
- Cause excessive daytime sleepiness
- Cause insomnia
- More wakeful stages during night
What is the most immediate and obvious consequence of sleep deprivation?
Cognitive impairment
What is the general function of sleep?
To allow the brain to rest
(exact reason is still unknown)
What are the three main reduced functions with sleep deprivation?
- Vigilance
- Attention
- Cognitive functions
What does the term neural oscillations refer to?
The term “neural oscillations” refers to the rhythmic and/or repetitive electrical activity generated
spontaneously and in response to stimuli by neural tissue in the central nervous system.
What are the 2 processes involved in sleep control?
*Process S (Homeostatic sleep pressure)
*Pressure C (Circadian rhythm)
What drugs can be used to induce sleep or sedation?
Benzodiazepines (e.g. temazepam and diazepam)
What can induced sleep or sedation be defined in relation to?
*Defined in relation to maintenance of verbal contact with a patients, who can still obey commands.
What is the SCN?
Suprachiasmatic nucleus in hypothalamus
What is the role of the hypothalamus in sleep?
It is essential for maintaining sleep-wake cycle. It contains SCN (body’s primary circadian clock) and VLP (ventrolateral preoptic nucleus which promotes sleep by inhibiting wakefulness-promoting regions)
What is the role of the basal forebrain in sleep
This area is involved in promoting wakefulness and REM sleep through its cholinergic neurons.
What is the role of the brainstem in sleep?
Contains several nuclei that are critical for maintaining wakefulness and REM sleep. The reticular activating system (RAS) in the brainstem is particularly important for arousal and wakefulness.
What is the name of the neuronal systems most critical to sleeping and waking?
Diffuse modulatory neurotransmitter systems
What are the common principles of the diffuse modulatory systems?
- Core of each system has a small set of neurons (several thousand)
- Neurons arise from central core of brain, mostly from brainstem
- Each neuron can influence many others - MANY synaptic contacts
- Transmitters released into ECF (not synaptic cleft) so can diffuse to many neurons rather than being confined
What are the effects of the noradrenergic diffuse system?
- Arousal - firing in exciting events in wakefulness
- Reward system
What are the three origins of the cholinergic diffuse system?
- Pontomesencephalotegmental complex
- Basal optic nucleus of Meynert
- Medial septic nucleus
What are the targets of the cholinergic diffuse system?
- Brainstem
- Neocortex
- Thalamus
- Hippocampus
What are the effects of the cholinergic diffuse system?
- Arousal
- Learning, short-term memory
- Possible important role in cognition - bc one of the first things to be lost in Alzheimer’s
What is another name for orexin?
Hypocretin
What are the origins of the orexin-producing neurons?
- Perifornical area
- Lateral hypothalamus
What are the targets of the orexin neurons?
- Entire cerebral cortex
- Brainstem
- Basal forebrain
What are the effects of the orexin neurons?
- Excite other diffuse systems: cholinergic, noradrenergic, serotonergic, dopaminergic, histaminergic
- Promote wakefulness, especially motivated behaviours
- Nutrient-sensitive: detect low glucose –> need to stay awake to find food
What is the role of GABA in sleep?
Activation of GABA neurons favours sleep
Mainly through inhibiting neurotransmission so that body and mind relax for sleep
