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Neuroscience (own deck) > Sleep and Circadian Rhythms > Flashcards

Sleep and Circadian Rhythms Flashcards

1
Q

what are the characteristics of sleep?

A
  • change in behaviour
  • change in brain activity
  • structural changes in neurons and glia
  • gene expression
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2
Q

what does sleep consist of?

A
  • cycles of non-REM and REM sleep
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3
Q

what is the behavioural definition of sleep?

A
  • reduced motor activity
  • reduced response to stimulation
  • stereotypic (eyes closed in humans)
  • easy reversibility
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4
Q

how can physiological activity be measured non-invasively?

A
  1. Electromyography (EMG): muscle movements
  2. electro-oculography (EOG): eye movements
  3. electroencephalography (EEG): brain activity
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5
Q

what is EEG?

A
  • 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
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6
Q

what are the advantages of EEG?

A
  • 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
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7
Q

what are the disadvantages of EEG?

A

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
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8
Q

what are the 4 main types of brain waves, from high to low frequency?

A
  1. beta = 13-30Hz
  2. alpha = 8-13Hz
  3. theta = 4-8Hz
  4. delta = 0.5-4Hz (large amplitude, slow oscillations)
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9
Q

what is non-REM sleep?

A
  • 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
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10
Q

what are the 4 main stages in non-REM?

A
  1. drowsiness - theta waves
  2. light-sleep
  3. deep-sleep - delta waves
  4. very-deep sleep - delta waves
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11
Q

what happens in drowsiness stage (1) during non-REM?

A
  • 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
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12
Q

what happens in light-sleep stage (2) during non-REM?

A
  • 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
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13
Q

what are K complexes?

A
  • occur episodically against background of continuing low-voltage EEG activity
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14
Q

what happens in deep-sleep stage (3) during non-REM?

A
  • 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)
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15
Q

what happens in very deep-sleep stage (4) during non-REM?

A
  • brain produces delta waves exclusively
  • disorientation or several minutes following arousal
  • slow wave activity dominates EEG record
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16
Q

what are stages 3 and 4 in non-REM sleep known as?

A

slow wave sleep

17
Q

how are the waves in each stages compared?

A

stage 1 = theta waves

stage 2 = low frequency waves with sleep spindles and K complexes

stage 3 and 4 = slow wave brain activity

18
Q

what is stage 5 of sleep?

A

REM sleep

19
Q

what is REM?

A
  • 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
20
Q

what happens during REM?

A
  • 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
21
Q

what is the normal sleeping pattern in humans?

A

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
22
Q

how much time is spent per stage of sleep in young adults?

A
  • 5% in stage 1
  • 50-60% in stage 2
  • 15-20% in stage 3 and 4
  • 20-25% in REM
23
Q

how is sleep regulated?

A
  • noradrenaline and serotonin neurons in brainstem
  • diffuse modulatory system controls rhythmic behaviour in hypothalamus
  • inhibition of motor neurons
24
Q

what causes wakefulness?

A
  • 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

25
Q

what causes non-REM?

A
  • decreased AP firing in brainstem

- sleep spindles correlate with increased activity in thalamus, creating delta rhythms

26
Q

what causes REM?

A
  • similar to AP firing in an awake stage, - no activity in frontal lobe, raphe nuclei or locus coeruleus
  • inhibition of motor neurons
27
Q

what are the theories of dreaming?

A
  • 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
28
Q

what are circadian rhythms?

A

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
29
Q

what do circadian rhythms require?

A

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

30
Q

what is the major internal clock of the circadian rhythm?

A

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
31
Q

what inputs into the suprachiasmatic nucleus?

A

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

Neuroscience (own deck) (14 decks)

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