Sleep and consciousness Flashcards
Give 3 measurements you can make to see whether someone is sleeping or to measure activity during sleep
- EEG - measures brain activity
- EOG - measures eye movement
- EMG - measures muscle activity
1) Describe the various stages of sleep and what happens to brain, eye and muscle activity as measured by EEG, EOG and EMG respectively
2) Explain the levels of activity in stage 5
1)
- Stage 1 + 2 - NREM: very low EEG, EOG and moderate EMG activity
- Stage 3+4 - NREM 2: moderate EEG, EOG and EMG activity but still considered NREM due to limited eye movement
- Stage 5 - REM: slightly less EEG activity than stage 4 but still moderate, EOG very high, EMG very low
2)
- Very high EOG - rapid eye movements occur hence REM sleep
- Very low EMG - muscle activity is supressed to prevent you from acting out your dreams
How long does a sleep cycle last?
90 minutes
Aside from sleep and muscle activity, what physiological visceral effects occur in REM sleep?
- Increased HR
- Increased respiration rate
What is the name of the system which controls arousal (wakefulness) ?
Reticular activating system
What is the pathway of the RAS and how does it stimulate arousal?
- From brainstem - locus coeruleus (noradrenergic) and ventral tegmental nuclei (dopaminergic)
- Projects to cortical areas such as the frontoparietal cortex either directly or…
- Indirectly via intralaminar nuclei of the thalamus
- It stimulates cortical activity
- The higher the activity of the RAS, the higher the cortical activity and thus the higher the level of arousal / wakefulness
Describe the hypothalamic nuclei / RAS axis control of wakefulness and sleep, excluding the mechanism of circadian rhythm
- RAS ultimately stimulates cortical areas to promote wakefulness
- LH (Lateral Hypothalamus) - orexin / hypocretin system (orexin secreting neurones) promotes RAS so promotes wakefulness
- VLPN (ventrolateral preoptic nucleus) inhibits RAS so inhibits wakefulness / promotes sleep
Describe the mechanism of the circadian rhythm, what regulates it, and how this interacts with the rest of the hypothalamic / RAS axis-type thing to regulate wakefulness
- Retina receives light and impulses are also sent along to the hypothalamus
- It stimulates the SCN (suprachiasmatic nucleus) within the hypothalamus
- The SCN then interacts with the VLPN (ventrolateral preoptic nucleus), the LH (lateral hypothalamus) and the RAS to influence wakefulness appropriately, dependent upon light levels in the environment so as to inhibit sleep when its bright outside and vice versa
- It also interacts with the pineal gland which secretes melatonin
What neurological (note not psychiatric like mood things because you can guess these really but neurological) effects does sleep deprivation have?
Also what may sleep problems be a warning sign for?
- Impaired attention
- Impaired memory
- Impaired executive function
- Sleep problems may be a warning sign for neurodegenerative disease
What somatic effects can sleep deprivation have?
- Glucose intolerance
- Reduced leptin / increased appetite → obesity
- Impaired immunity
- Increased risk of CVD and cancer
How does sleep after sleep deprivation change?
- Reduced latency to sleep onset
- Increased slow-wave (NREM) sleep
- Increased REM sleep (if after selective REM deprivation)
Functions of sleep?
- Restoration and recovery
- Specific brain functions e.g. memory consolidation
Give 4 common causes of sleep problems
- Insomnia
- Narcolepsy
- Shift work
- Lewy-body disease
Give some causes of insomnia
- Sleep apnoea
- Chronic pain
- Depression
- Fatal familial insomnia
- Night shifts
Give a drug used for treating insomnia and how it works
- Hypnotics
- Inhibit GABAergic circuits
What are the 2 factors that could lead to narcolepsy and what is narcolepsy often associated with?
- Orexin deficiency (LH inhibited) - so less activation of RAS so you sleep loads but during the day often which disrupts your ability to sleep at night
- Dysfunction of control of REM sleep
- Associated with cataplexy - sudden, brief loss of voluntary muscle tone, often triggered by strong emotions
Lewy-body disease is a type of …..
What are the sleep symptoms of Lewy-body disease?
- Sleep disorder where sleep is interrupted
- Also, when actually sleeping, patients will often act out dreams somewhat - have voluntary muscle movements in accordance with dreams
What are the 3 elements of consciousness?
- Level of consciousness: drowsy or wide-awake?
- Content of consciousness: what are you conscious / aware of?
- Conscious self
What is the difference between vigilance / arousal and awareness?
- Vigilance / arousal is to do with level of wakefulness associated with RAS activity
- Awareness is to do with level and content of consciousness
How can we measure brain activity in vivo using Perturbational Complexity Index (PCI) and how can it be used to identify the presence of sleep disorders?
- Use transcranial magnetic stimulation to stimulate the brain - there is a reverberation of activity
- This reverberation of activity can be measured using EEG
- This response is not as diverse or complex in people with sleep disorders than in normal people
What is neural correlates of consciousness and how is it carried out?
- The minimum neuronal mechanisms jointly sufficient for any one specific conscious experience
- You show graded levels of experience stimulus e.g. less and less pixelated image until it eventually becomes clear and recognisable
- You measure the activity in the brain and you see what parts are active just before you recognise the stimulus
- You then repeat this with activity in the brain once you finally first recognise the stimulus
- You then look at the difference in brain activity in between these points to see what parts are really involved in the conscious recognition
Compare the following in terms of …
- Arousal and awereness
- Behaviour / action capability
- Sleep-wake cycles
- Coma
- Vegetative state
- Minimally conscious state
- Coma
- Unrousable
- No awareness
- Abnormal sleep-wake cycles
- No action / behaviour capability
- Vegetative state
- Rousable as normal
- Little awareness but more than in coma
- Sleep-wake cycles as normal
- Reflexive / spontaneous actions / behaviours
- Minimally conscious state
- Rousable as normal
- Moderate awareness but still low - higher than in vegetative state and coma though
- Limited actions and behaviours
What causes coma pathophysiologically?
- Damage to RAS
What causes vegetative state pathophysiologically?
- Normal RAS
- Damage to cortex and hemispheres
What causes locked-in syndrome and what is still intact?
- Intact cortex
- Intact RAS
- Damaged ventral Pons
What happens in brainstem death?
- Irreperable damage to the brainstem
- Causes loss of brainstem-mediated reflexes
- Causes loss of brainstem-mediated respiratory drive
How do the various abnormal states of consciousness affect breathing and how to manage?
- Vegetative state / minimally conscious - may need tracheostomy but respiratory drive is preserved
- In brainstem death, there is loss of respiratory drive
1) What is homonoymous hemianopia and what is it common in?
2) What other pathology is it often confused with, and what happens in this?
1)
- Lose half your field of vision
- Common in stroke
2)
- Neglect - a consciousness defect - you lose conscious awareness of the side
What are the different waves in an EEG and what frequency do they operate, thus rank them in order of frequencies?
- Delta - 4 Hz
- Theta - 4-8 Hz
- Alpha - 8-13 Hz
- Beta - 13-30 Hz
- Gamma - roughly 40 Hz
When do gamma waves appear in the EEG?
- Gamma waves are higher frequency neural oscillations that are shown on the creation of conscious contents in the mind via thalamo-cortical feedback loops
How do alpha waves vary and what do they vary based on?
- Attentive - slow
- Relaxed - fast
- Absent - pathology
