Sleep wake cycle and insomnia Flashcards
Describe the role of arousal centres
-when awake, areas in the brainstem and hypothalamus called arousal centres stimulate the cerbral cortex
-arousal centres release neurotransmitters including ACh, histamine,5HT and orexin
Describe the sleep promoting centre
-the ventrolateral preoptic nucleus in hypothalamus switches off arousal centres
-VPLO produces neurotransmitters GABA and galanin
-neurotransmitters cause arousal centres to shut down resulting in rapid changes into NREM sleep
What is the sleep switch?
-mutual inhibition between wake-promoting neurons from the arousal centre and sleep-promoting neurons from the VPLO
-when cortex is activated by the sleep arousal centres there is a simultaneous inhibition of VLPO
What happens when the arousal centre is stimulated?
histamine,5HT,NA stimulate the cortex promoting wakefullness and stops the messsage that makes us sleep
What happens when we recieve the message to sleep?
-if histamine is released and inhibited then sleep will ensue
-happens because the VPLO blocks the production of histamine and other wake signs by GABA and galanin
-but histamine also blocks VPLO in which case switch will flip to wake state
what is inhibited when you are awake and what is inhibited when you are asleep?
awake-GABA and galanin
sleep - histamines
What are the two proccesses of the sleep wake cycle?
-24 hour circadian rythum of sleep and arousal-proccess c
-a sleep wake timer-homeostatic mechanism-proccess s
Describe the circadian rhytm-proccess c
-the suprachiasmatic nucleus communicates the circadian rhythm to the body via the production of melatonin
-melatonin production by the pineal gland peaks in the middle of the night.
-melatonin does not induce sleep but simply signals the start of sleeping process
What does the circadian rhythm control?
Tendency to sleep
Sleep structure
Level of alertness
Temperature regulation
Hormone production
Melatonin
Growth hormone
Cortisol
Cardiovascular function
Respiratory function
Glucose levels
How is the SCN reset?
every daytime by light and every night time by melatonin
Describe the homeostatic mechanism-proccess s
-Homeostatic mechanism ‘counts’ how long we have been awake or asleep and a ‘sleep pressure’ builds up with increasing wakefulness
-The longer you remain awake, the higher the sleep pressure
-As you sleep, the sleep pressure reduces and the likelihood of awakening increases
What is sleep pressure?
the accumulation of adenosine in the cerebrospinal fluid whilst awake
Describe the role of adenosine with regards to sleep pressure
-Adenosine is released from ATP as energy from glycogen is used during the day so levels increase the longer you are awake
-Adenosine levels will drop during sleep as glycogen stores are replenished
-Stimulants such as caffeine and theophylline (tea and chocolate) act as adenosine receptor antagonists and so reduce its ability to induce sleepiness
Describe homeostatic system and circadian rhythm during the night
-during the first half of sleep the sleep pressure is still high whilst the circadian alerting signal has decreased
-sleep drive now has been reduced however the persistant low circadian alerting signal maintains sleep
-synchronization of these two systems allow consolidation periods of both alertness and sleep
What external factors influence the quality of sleep we obtain?
-light
-pain
-medical condtions
-medication
-alcohol
-caffeine
-sleep environment
Describe how light effects sleep
-light modulates circadian rhythm by influencing the timing of SCN
-light stimulates photosensitive cells of the retina which signal to the SCN via retinohypothalamic tract
-exposure to light during the night can reset the internal clock making sleep diffcult
How does medication affect sleep?
-alpha and beta blocker reduce REM and NREM3 sleep and increases daytime sleepiness
-some antideppresants provoke insomnia, reduce REM sleep
-brain cells promoting alertness are inhibted by adenosine
Why is caffeine a stimulant?
it is an adenosine receptor antagonist and so removes the inhibition by adenosine resulting in increased alertness
what are the 6 main catergories of sleep disorders?
-insomnia
-sleep related breathing disorders (obstructive sleep apnoea
-central disorders of hypersomnolence-narcolepsy
-circadian rhythm sleep wake disorders
-parasomnias
-sleep related movement disorders
What are the four main catergories of insomnia?
-chronic insomnia disorder
-short term insomnia disorder
-other insomnia disorder
-isolated symptoms and normal variant
What are the main symptoms of chronic insomnia?
-difficulty initiating sleep
-difficulty maintaining sleep
-waking up earlier than desired
When does chronic insomnia occur?
At least three times a week
-has been present for at least 3 months
describe primary and secondary insomnia
p-main condtion
s-caused from another condition
What are the identifiable groups of chronic insomnia?
-Psychophysiological insomnia
-idiopathic insomnia
-paradoxical insomnia
