Sleep and Circadian Rhythms Flashcards
what are the characteristics of sleep?
- change in behaviour
- change in brain activity
- structural changes in neurons and glia
- gene expression
what does sleep consist of?
- cycles of non-REM and REM sleep
what is the behavioural definition of sleep?
- reduced motor activity
- reduced response to stimulation
- stereotypic (eyes closed in humans)
- easy reversibility
how can physiological activity be measured non-invasively?
- Electromyography (EMG): muscle movements
- electro-oculography (EOG): eye movements
- electroencephalography (EEG): brain activity
what is EEG?
- measures synchronous electrical activity from populations of neurons in brain
- electric field created by ionic movements
- electrodes are placed on scalp to detect electric fields
- linked to electrical amplifier and to a monitor
- different electrodes record different patterns of activity
what are the advantages of EEG?
- non-invasive
- easy to administer
- data easily generated
- large amounts of data from different brain areas
- high temporal resolution (milliseconds) so can detect quick changes in brain activity
what are the disadvantages of EEG?
low spatial resolution:
- electric fields follow an inverse square law so only cortical activity is detectable
- as distance increases from the electrical field, charge intensity decreases (detection decreases)
- distance from neurons to electrode is ~1cm through the scalp
what are the 4 main types of brain waves, from high to low frequency?
- beta = 13-30Hz
- alpha = 8-13Hz
- theta = 4-8Hz
- delta = 0.5-4Hz (large amplitude, slow oscillations)
what is non-REM sleep?
- low neuronal activity, little AP firing
- metabolic rate and brain temperature at their lowest
- heart rate and blood pressure decline
- decreased sympathetic outflow
- increased parasympathetic outflow
- muscle tone and reflexes in tact
- some muscular activity in all non-REM stages
what are the 4 main stages in non-REM?
- drowsiness - theta waves
- light-sleep
- deep-sleep - delta waves
- very-deep sleep - delta waves
what happens in drowsiness stage (1) during non-REM?
- awakened easily
- eyes move slowly and muscle activity slows
- transition from wakefulness to onset of sleep (lasts several mins)
- sinusoidal alpha activity 20-40microvolts at 10Hz
- EEG = low voltage activity and theta waves
- some muscular activity
- people have sensation of falling
what happens in light-sleep stage (2) during non-REM?
- eye movement stops
- brain waves slower with burst of rapid brain waves
- body temp drops and HR slows
- bursts of sinusoidal waves called sleep spindles (12-14Hz) and biphasic waves called K complexes
what are K complexes?
- occur episodically against background of continuing low-voltage EEG activity
what happens in deep-sleep stage (3) during non-REM?
- slow delta waves interspersed with small faster waves
- sleep-walking, night-terrors, talking during sleep and parasomnia
- occurs during transitions between non-REM and REM sleep
- slow delta waves (0.5-2Hz)
what happens in very deep-sleep stage (4) during non-REM?
- brain produces delta waves exclusively
- disorientation or several minutes following arousal
- slow wave activity dominates EEG record
what are stages 3 and 4 in non-REM sleep known as?
slow wave sleep
how are the waves in each stages compared?
stage 1 = theta waves
stage 2 = low frequency waves with sleep spindles and K complexes
stage 3 and 4 = slow wave brain activity
what is stage 5 of sleep?
REM sleep
what is REM?
- EEG mimics wakefulness
- closed eyes move rapidly from side to side
- similar to stage 1: low voltage and mixed frequency
- paradoxical sleep: REM-neuronal firing similar to wakefulness, but the muscles are still relaxed so there is no movement
what happens during REM?
- brain temp and metabolic rate rise due to increased neuronal activity
- some areas more neuronal activity than there would be when awake
- all skeletal muscles are atonic (paralysed)
- muscles controlling eye, ear ossicles and diaphragm remain active to enable breathing and hearing of danger
what is the normal sleeping pattern in humans?
REM and non-REM sleep alternate cyclically:
- at 70-80 mins, sleeper returns to stage 2 or 3 before entering first REM phase which lasts 8-10 mins
- time from first stage to end of REM = 90-100 mins
- repeated 4 or 5 times per night
- during each repetition, stages 3 and 4 decrease in duration and REM increases
how much time is spent per stage of sleep in young adults?
- 5% in stage 1
- 50-60% in stage 2
- 15-20% in stage 3 and 4
- 20-25% in REM
how is sleep regulated?
- noradrenaline and serotonin neurons in brainstem
- diffuse modulatory system controls rhythmic behaviour in hypothalamus
- inhibition of motor neurons
what causes wakefulness?
- activation of neurons in brainstem precedes awakening
- stimulation of brainstem causes awakening, as depolarisation causes neurons to fire many APs
lesion of brainstem causes coma
what causes non-REM?
- decreased AP firing in brainstem
- sleep spindles correlate with increased activity in thalamus, creating delta rhythms
what causes REM?
- similar to AP firing in an awake stage, - no activity in frontal lobe, raphe nuclei or locus coeruleus
- inhibition of motor neurons
what are the theories of dreaming?
- strange imagery due to the brain not fully functioning
- sleep exercises synapses when there is no external activity
- memory consolidation
- circuit testing to check that everything is working correclty
what are circadian rhythms?
endogenous periodicity of 24 hours between sleep and wakefulness
- persist without environmental cues
- modulated by external timing cues called zeitgeers which adapt the rhythm to the environment
what do circadian rhythms require?
sensory information
- light going off is an external cue that maintains the circadian clock
if the external cue is removed, the circadian rhythm is shifted
what is the major internal clock of the circadian rhythm?
Suprachiasmatic nucleus of the anterior hypothalamus
- lesioning of the suprachiasmatic tract interferes with circadian rhythm
- the suprachiasmatic nucleus regulates timing of sleep, but is not responsible for sleep itself
what inputs into the suprachiasmatic nucleus?
intrinsically photosensitive ganglion cells send info from retina to the nucleus
- these cells respond to light
- even if photoreceptors are removed, they can still detect changes in light intensity
