Sleep

Question 1

organization of sleep

Answer 1

continuum - specific stages but no distinct divisions
nREM and REM sleep alternate - each cycle ~90min
4-6 cycles in sleep period

Question 2

EEG

Answer 2

observe changes on scalp - define sleep stages
neurophysiology of specific wave forms
measures oscillations in voltage transmitted from the brain

Question 3

brain rhythms

Answer 3

delta: 0-3.99 Hz
theta: 4-7.99 Hz
alpha: 8-13 Hz
beta: >13 Hz

Question 4

states of sleep

Answer 4

awake: presence of alpha rhythm
nREM sleep: N1, N2, N3
REM sleep: no muscle tone and rapid eye movement

Question 5

nREM sleep

Answer 5

N1 - alpha drop out (no alpha rhythms)
N2 - sleep spindles and K complexes - 11-16 Hz
N3 - slow wave sleep

Question 6

sleep spindles

Answer 6

represent hypersynchronicity (risk for seizures if epileptic)
in central temporal region

increased reticular neuron activity hyperpolarizes relay neurons via GABA-B receptors (inhibitory input)
hyperpolarization activates T-type Ca2+ channels → low threshold depolarization + bursts of thalamo-cortical activation by relay neurons
- circuit is active in absence seizures = excessive synchronous activity

Question 7

relay neurons

Answer 7

excitatory input to cortex
inside thalamus (reticular neurons are outside of thalamus)

low threshold depolarization: can depolarize from hyperpolarized state

Question 8

benzodiazepines

Answer 8

associated with increased stage N2 sleep, increased spindle activity - possibly due to increased GABA-ergic signalling

Question 9

slow waves

Answer 9

delta waves - implicated in learning and memory

Question 10

REM sleep

Answer 10

rapid eye movements = dreams
lighter phase of sleep - EEG looks awake (absence of sleep waves)
progressively increases through night - about half of U5 stage

Question 11

neurobiology of sleep

Answer 11

glutamate = excitatory → wakefulness
GABA = inhibitory → sleepiness

Question 12

Wakefulness

Answer 12

glutamate is secreted by
1. parabrachial/precoeruleus nuclei (pons)
2. supramammillary nuclei (midbrain)

excitatory transmission from brainstem nuclei
1. causally to motor neurons in the spinal cord
2. rostrally to neurons throughout the cortex

thalamo-cortical transmission is supported via dorsal pathway using acetylcholine to maintain consciousness

Question 13

acetylcholine

Answer 13

maintain consciousness
secreted from the basal forebrain
cholinergic neurons in pons (pedunculopontine tegmentum and laterodorsal tegmentum) project to thalamus

highly active during wakefulness
population in pons is active in REM sleep

Question 14

rostral excitatory transmission

Answer 14

from brainstem nuclei to neurons in cortex
histamine - from tuberomammillary nucleus
dopamine - from ventral tegmental area
serotonin - from raphe (pons)
norepinephrine - from locus ceruleus (pons)

Question 15

nREM sleep transmission

Answer 15

inhibitory synaptic transmission (GABA) from the ventrolateral preoptic nucleus (hypothalamus) to all of brainstem nuclei important in wakefulness → inhibition of normal wakefulness pathway

Question 16

REM sleep transmission

Answer 16

REM-on neurons in the PPT and LDT (cholinergic)
1. excitatory connection to thalamus = awake-looking EEG
2. excitatory connection to glycinergic neurons in medial medulla - inhibit motor neurons in the spinal cord = muscle atonia

Question 17

hypocretin (orexin)

Answer 17

produced by cells in hypothalamus
provide inputs to various nuclei important in sleep to support and stabilize sleep states
1. promotes wakefulness
2. stabilize wake-sleep transitions
3. maintenance of skeletal tone during wakefulness

lower levels in narcolepsy

Question 18

adenosine

Answer 18

mediator of sleepiness after prolonged wakefulness
promotes transition to slow wave sleep by inhibiting basal forebrain neurons (= maintenance of wakefulness)
caffeine = adenosine antagonist

Question 19

melatonin

Answer 19

release from pineal inhibited by light stimulating suprachiasmatic nucleus in hypothalamus
darkness releases the pineal from SCN inhibition = melatonin release
acts across neuronal population to suppress glutamatergic neurons → less activity

Question 20

symptoms of abnormal sleep

Answer 20

excessive daytime sleepiness
insomnia
abnormal movements during sleep
awakenings (parasomnias)
abnormal breathing during sleep (sleep apnia)
sleep paralysis
hallucinations

Question 21

insufficient sleep syndrome

Answer 21

most common cause of sleepiness
affects body + brain → weight gain, high blood pressure, diabetes, altered activity of hormones can lead to obesity
hippocampus, seizures, memory, mental health

Question 22

Obstructive Sleep Apnea Syndrome

Answer 22

second most common cause of sleepiness
temporary pause in breathing while sleeping - muscle tone diminishes + airway collapses
awakened by effort of breathing against closed airway

obesity and snoring
increased risk of heart attack and stroke
treat with CPAP

Question 23

narcolepsy

Answer 23

excessive daytime sleepiness with sleep attacks
cataplexy - sudden temporary loss of muscle tone (no loss of awareness)
sleep paralysis
hallucinations - hypnogogic: while falling asleep; hypnopompic: while waking up

low levels of hypocretin (stabilizing sleep-wake transitions) = frequent + inappropriate transitions between sleep and wakefulness
REM-on neurons turn on inappropriately = paralysis of REM sleep while awake (cataplexy)

Question 24

abnormal movements during sleep

Answer 24

classified by timing during sleep period
- N1-N2: sleep-wake transition movements
- N2-N3: disorders of arousal
- REM: REM sleep behaviour disorder, nightmares, sleep paralysis

Question 25

restless legs syndrome

Answer 25

when attempting to fall asleep
uncomfortable sensations in legs with urge to move them
family history
iron-deficiency anemia; pregnancy
treatable by treating symptoms - commonly iron supplementation

Question 26

parasomnias

Answer 26

abnormal movements or behaviours intruding into sleep
nREM sleep - disorders of arousal: confusional arousals, sleep terrors, sleepwalking
REM sleep: REM sleep behaviour disorder

Question 27

sleep terrors

Answer 27

arise out of slow wave sleep
more common in kids
associated with sleep-walking and confusional arousals
family history

Question 28

REM sleep behaviour disorder

Answer 28

loss of REM atonia
act out dreams
more common in elderly - associated with Parkinson’s disease and dementia with Lewy bodies

degeneration of glycinergic neurons in medulla → loss of REM atonia