Arousal & sleep Flashcards
What are the different types of dendritic structures found in the reticular formation?
- Isodendritic: Dendrites radiate in uniform directions over large distances (diffuse), usually perpendicular to the axis of the brainstem. This is the most common form of dendrite arrangement.
- Allodendritic: More specialised dendritic radiations in a smaller area.
- Idiodendritic: Dendrites are located within very small and specialised nuclei within the brainstem.
What are the longitudinal zones of the reticular formation?
- Raphe: Close to the midline
- Medial zone: Contains many large neurones with long descending axons involved in motor control
- Lateral zone: Contains smaller neurones with short ascending axons involved in sensory-related tasks
What are the functions of the reticular formation?
- Ascending projection: Involved in regulation of levels of activity in the brain (such as those involved in sleep, attention, arousal…)
- Descending projections: Involved in stereotyped motor activities (such as swallowing, chewing, vomiting, sneezing, eye movements…) as well as control of basic involuntary actions (such as breathing and cardiovascular control)
What are the rostral continuations of the reticular formation?
Lateral hypothalamus and subthalamic regions
What are the caudal continuations of the reticular formation?
Intermediate grey of the spinal cord
What are the projections of the reticular formation into the cortex?
- Direct: Via medial forebrain bundle (through lateral hypothalamus)
- Indirect: Via intralaminar nuclei of thalamus
What are the different neurotransmitters used by the cortical projecting RF neurones?
- NA
- 5-HT
- DA
- ACh
What are the origins and functions of NA neurones from RF?
Origins: Locus ceruleus
Functions: Increases general cortical responses to sensory stimuli, increasing cortical signal-to-noise ratio
What are the origins and functions of the DA neurones from RF?
Origins: Ventral tegumental area, substantia nigra
Functions:
- Projections into ventral striatum: Mediates appetitive motivated behaviours
- Projections into dorsal striatum: Mediates gating of motor activity and thus consummatory behaviours
What are the origins and functions of the 5-HT neurones from RF?
Origins: Raphe nucleus
Functions: May be involved in gating and inhibition of impulsive responses to sensory stimuli
What conditions are related to defects in the 5-HT system?
Obsessive compulsive disorders
What are the origins and functions of the ACh neurones from RF?
Origins: Various (inc. substantia innominata)
Functions:
- Forebrain projections: Learning and memory
- Thalamus: Gating sensory information access to the cortex
- Peduncopontine projections: Sleep
What are electroencephalograms (EEGs)?
Measurements are taken as electrical activity from the scalp, usually as a result of summation of slow changes in membrane potentials (e.g. EPSPs, IPSPs) in cortical neurones.
What is the general relationship between cortical activity and EEG?
Lower activity → Higher amplitude EEGs
What are the types of EEG waveforms?
- Delta (<4 Hz)
- Theta (4-7 Hz)
- Alpha (8-15 Hz)
- Beta (16-31 Hz)
- Gamma (>32 Hz)
What types of activities are associated with delta waves?
- Slow-wave (deep) sleep – adult
- Babies
What types of activities are associated with theta waves?
- Young children
- Drowsiness (adults)
- Inhibition of responses
What types of activities are associated with alpha waves?
- Relaxation
- Resting (closing eyes)
What types of activities are associated with beta waves?
- High frequency, low amplitude
- Thinking/focus
- Anxiety
- Stress
What types of activities are associated with gamma waves?
- Integration of sensory modalities
- Memorisation tasks
What are the stages of non-REM sleep?
- Stage 1 (Drowsy period): Falling asleep, whereby the high frequency, low amplitude waves of the awake state give way to lower frequency, higher amplitude waves. This stage is characterised by theta waves.
- Stage 2 (Light sleep): Further decrease in frequency of synchronised brain activity, with occasional high frequency spikes.
- Stage 3 (Moderate-deep sleep): Further decrease in frequency and increase in amplitude of waves.
- Stage 4 (deep sleep): Stage of sleep with the lowest frequency and highest amplitude of synchronised activity waves known as delta waves.
What is the general pattern of change in EEGs as one descends from wakefullness into deep sleep?
- ↑ Amplitude
- ↓ Frequency
What are the physiological changes that occur during non-REM sleep?
- Decreased muscle tone
- Decreased heart rate
- Decreased breathing rate
- Decreased blood pressure
- Decreased metabolic rate
What are the physiological changes that occur during REM sleep?
- Increased blood pressure
- Increased heart rate
- Increased metabolic rate
- Rapid eye movements
What is the general shape of the sleep cycle?
- 90 minute cycles alternating between REM and non-REM sleep
- Progressively shallower sleep as the sleep cycle continues
What are the possible functions of sleep?
- Restoration of physiological/neurological function
- Brain development (children)
- Memory consolidation
What are the neural changes that occur during wake → non-REM sleep transition?
- ↓ ACh (peduncopontine)
- ↓ NA
- ↓ 5-HT
What are the neural changes that occur during the non-REM sleep → REM sleep transition?
- ↑ ACh (peduncopontine)
- ↓ NA
- ↓ 5-HT
What are the changes in the cortex that occur in sleep?
- Non-REM: Cortical activity depressed so that there are no cognitive processes present
- REM: Cortical activity analogous to wakeful state and cognitive processes are present but sensory inputs and outputs are inhibited (i.e. cortex disconnected from outside world)
What is the flip-flop model for control of sleep-wakefulness?
- There is mutual inhibition between the ventrolateral preoptic area (VLPA) that promotes sleep and the RF arousal systems (e.g. NA, 5-HT…) that promote wakefulness.
- Balance between inhibition of these 2 components determine whether individual is asleep or awake.
- External systems alter this balance and thus together control sleep-wakefulness.
What is narcolepsy?
Frequent, sudden attacks of REM sleep during day for a few minutes. This may be accompanied by cataplexy (loss of motor control).
What is narcolepsy possibly caused by?
Mutations in orexin gene
What is the relationship between feeding and sleep?
- Hunger inhibits sleep while satiety promotes sleep
- Due to high [orexin] during hunger and low [orexin] during satiety
Which part of the brain is resposible for circadian rhythms?
Suprachiasmatic nucleus (hypothalamus)
What is the main mechanism by which circadian rhythms are synchronised to the day-night cycle?
Blue light (zeitgeber) detected by melanopsin in ipRGCs
What is a pathway by which circadian rhythms may be used to control sleep?
SCN → Dorsomedial nucleus (DMN) of hypothalamus → VLPA hypothalamus (promotes sleep)
