L17 Sleep And Circadian Rhythms Flashcards
What does REM stand for?
Rapid eye movement
What is sleep defined as behaviourally? (4)
- Reduced motor activity
- Reduced response to stimulation
- Stereotypic postures (eye closed in humans)
- Relatively easy reversibility
What changes occur when sleeping?
- Change in behaviour
- Change in brain activity
- Structural changes
- Gene expression (some genes expressed/under expressed)
What 3 ways can physiological activities be conveniently measured using electrical recordings?
- Muscle movements with electromyography (EMG)
- Eye movements with electro-oculography (EOG)
- Brain activity with electroencephalography (EEG)
What does the electroencephalogram (EEG) do?
It measures the synchronous, electrical activity from large populations of neurones in the brain
How does the EEG work?
Cellular, ionic movement creates an electric field which spreads across many millions of neurones.
Electrodes placed on the surface of the scalp detect these electric fields linked to an electric amplifier and to a monitor.
Why do we use the electroencephalogram (EEG)?
- Non-invasive
- Easy to administer
- Data easily gathered
- High temporal resolution
What is the one downside to the EEG?
It has a low spatial resolution meaning the electric fields follow an inverse square law so only cortical activity can be detected
What are the main 4 types of brain waves?
- Beta: (13-30 Hz)
- Alpha: (8-13 Hz)
- Theta (4-8 Hz)
- Delta (0.5-4Hz)
What are the 4 main stages of non REM sleep?
1) Drowsiness
2) Light sleep
3) Deep sleep
4) Very deep sleep
What physiological effects occur when in Non-REM sleep ?
- Muscle tone and reflexes are intact
- Neuronal activity is low- not much action potential firing between neurones
- Metabolic rate and brain temperature at their lowest
- Heart rate and blood pressure decline - decreased sympathetic nervous system outflow
- Increase in parasympathetic nervous system
What is expected to see from EOG, EMG, EEG from stage 1?
EOG - Eyes show slow, rolling movements
EMG - During stage 1 and all non-REM some muscular activity
EEG - Low voltage activity if mixed frequencies (mostly theta waves)
What physiological changes are expected in stage 2?
- Eye movement stops and brain waves becomes slower with only an occasional burst of rapid brain waves.
- Body temperature drops, heart rate slows
What waves are expected during stage 2?
Bursts of sunisoidal waves called ‘sleep spindles’ (12-14Hz) and biphasic waves called K complexes
What is deep sleep characterised as?
Extremely slow delta waves are interspersed with smaller, faster waves.
What occurs during the transitions between non-REM and REM sleep?
Sleepwalking, night terrors, talking during one’s sleep, and bedwetting ‘parasomnia’.
Which type of brain wave is expected at stage 3?
High amplitude of slow delta waves (0.5- 2Hz)
What brain waves are expected at stage 4?
Brain produces delta waves almost exclusively
In summary, what typical brain waves of sleep and wakefulness are recorded using the EEG at every stage?
- Stage 1 - theta waves (4-7Hz)
- Stage 2 - sleep spindle (11-15Hz) and K-complex
- Stage 3 - slow aves (0.5-2.0Hz)
What is stage 5?
Rapid Eye Movement (REM) sleep.
- EEG during human REM is similar to stage 1/ awake.
Why are the brain waves similar during the awake stage and the stage 5 REM?
- Brain is hightly active during both wakefulness and REM stage.
What physiological stages occur during REM sleep?
- Brain temperature and metabolic rate rise - consistent with increased neural activity (in some areas - greater than in waking)
- All skeletal muscles are atonic - flaccid and paralysed
- Muscle controlling movements of the eye, middle ear ossicles, and diaphragm remain active (so you can breathe and hear any impending danger)
Does REM and non-REM sleep alternate cyclically?
Yes. After 70-80 minutes sleeper returns to stages 3 or even 2 before entering first REM phase which lasts 8-10 minutes. Repeated four or five times per night. Stages 3 and 4 decrease in duration and REM increases
How is sleep regulated?
Diffuse modulatory neurotransmission system
NE and 5-HT neurons in the brain stem
- Diffuse modulatory system controls rhythmic behaviour in the Thalamus
- Inhibition of motor neurons
How can we depict that the brain stem is responsible for wakefulness ?
Activation of neurons in brain stem precedes awakening.
Stimulation of brain stem causes awakening
(Lesions of the brain stem can cause sleep and coma)
What are the neurological effects of the Non- REM stage?
- Decrease of firing in the brain stem
- Spindles - correlated activity in the thalamus
- Delta rhythms: actvitity in the thalamus
What are the neurological effects of REM stage?
- Fairly similar to firing an awake state
- No activity in the frontal lobe
- No activity in Raphael nuclei and locus core unless
- Inhibition of motor neurons
How are circadian rhythms regulated within the 24hr periodicity?
They are modulated by external timing cues - zeitgebers (so the sun rise and sun set)
They adapt to the rhythm to the environment
What regulates the circadian rhythm internally?
Major internal clock is suprachiasmatic nucleus of anterior hypothalamus
(Must regulate timing of sleep rather the sleep itself)
What is the major internal clock?
The suprachiasmatic nucleus of anterior hypothalamus
What does the suprachiasmatic nucleus do?
It regulates timing of sleep (not the sleep itself)
