Week B1 Memory & Sleep II Flashcards
What are dreams?
Vivid mental experiences during REM sleep
Experienced whilst not fully conscious. Levels of bizarreness vary.
Recognized as a type of conscious experience, if woken during dreams
What is the sequence of REM/NREM sleep throughout the night?
With each cycle, REM sleep gets longer
What is the best theory for the function of sleep?
Memory consolidation: REM sleep appears to be a replay of the days activities, occuring whilst the cortex is disconnected
How does REM sleep change as we age?
Amount of REM sleep decreases with age, suggesting it has to do with consolidation of new information/experiences (i.e. newborns and v young infants require the most)
What is Instructional Replay?
The hippocampus recreates recent experiences, activating specific parts of the cortex
Over time, the linkages between those specific parts of the cortex become reinforced.
Eventually, they are independent of the hippocampus.
How does consolidation occur during sleep?
Research suggests…
Consolidation requires alternation between NREM and REM sleep.
Suring Slow Wave Sleep (NREM), the hippocampus appears to have more control over the cortex. This is when Instructional Replay can occur - formation of linkages from the hippocampus to the cortex, which eventually strengthen independently of the hippocampus.
Define Circadian Rhythm
Major sleep/wake cycle that runs at ~24-25 hours
Define Zeitgebers
Environmental influences that synchronise the 24-25 hour circadian rhythm to the specific environment - i.e. the force that chiefly synchronises this force with light/dark in the environment (via the melanopsin visual system). Other zeitgebers influences include social interactions, etc.
Define Ultradian Rhythm
90-minute cycle/rhythm that occurs during sleep and wakefulness
Generated by the medulla
A time-keeping mechanism operating on the cellular level
Describe the neurological drive of wakefulness
- Structures involved
- Key neurotransmitters involved
Nuclei in the brainstem (of the Ascending Arousal System) send diffuse axons to the cortex and thalamus, stimulating wakefulness
Cholinergic drive from Pons to Thalamus also involved
Key Neurotransmitters involved in waking: NA Histamine DA 5-HT Orexin
(ACh drives slow wave sleep)
Describe the Orexin System
& where is originates
Arousal Neurotransmitter System
Originating in the lateral/posterior Medial Zone of the hypothalamus, it sends projections to the arousal nuclei
Couples sleep/wake cycles to metabolic cycles
*Autoimmune depletion of Orexin has been found in people with narcolepsy
Describe the neurological control/inducement of sleep
The Ventrolateral Preoptic Nucleus (VLPO) sends inhibitory GABA and Galanin projections to the Ascending Arousal Nuclei to promote sleep
The Suprachiasmic Nucleus (SCN) also controls all circadian processes in the body, and induces the VLPO to suppress the Ascending Arousal Nuclei to induce sleep
Although the SCN is a big player, the ultimate decision to fall asleep is made by the Dorsomedial Hypothalamus (DMH), which uses the VLPO to shut down the cortex
How is light used as a zeitgeber for the circadian rhythm?
The Suprachiasmic Nucleus (SCN) of the Hypothalamus uses light as a zeitgeber for the circadian rhythm
Recently identified melanopsin visual pathway tells the Suprachiasmic Nucleus when it is light, which influences the circadian rhythm
What are the functions of the Suprachiasmic Nucleus (SCN)?
Location?
“Master Clock”
Controls all circadian processes in the body
Also cues the VLPO Nucleus to induce sleep
Regulates core body temperature as a timing signal for clocks in various tissues
Anterior Periventricular Region of Hypothalamus
Note: Body temperature is affected by feeding and activity, etc. This has an effect on body clocks except for the SCN clock***
Describe Circadian Temperature Variation
There is a drop of ~0.6-0.8 degrees, peaking at ~5am (during sleep)
Organ clocks are especially sensitive to this variation in body temperature
This drop in temperature is mostly instrinsic - not dependent on physical activity
Regulated to Suprachiasmic Nucleus (SCN)
Functions of the Dorsomedial Hypothalamus
Triggers sleep when appropriate
Although the SCN is major player in inducement of sleep, the DMH is the ultimate decision maker
Also regulates other core physiological mechanisms
What regulates the stages of sleep?
Regions of the brainstem and midbrain.
Geting by Thalamic Nuclei prevents stimuli from reaching the cortex
What regulates REM sleep?
Pontine Nuclei
Send cholinergic neurons to the Thalamus, and projections to inhibit skeletal muscle movements (aside from respiratory muscles, duh)
Describe the relationship between sleep and metabolism, and the metabolic repercussions of sleep deprivation
During slow wave sleep, growth hormone is upregulated and cortisol is suppressed. This impacts glucose metabolism.
Thus, chronic sleep deprivation leads to insulin resistance -> can cause Type II Diabetes
Sleep apnoea often does this -> Thus forms part of the “Syndrome X” / “Metabolic Syndrome” Cluster
List the major disorders of sleep:
Insomnia
Parasomnias (group)
- Narcolepsy
- Cataplexy
- REM behaviour disorder
- Slow wave disorders: night terrors, somnambulism, bedwetting
NB: Apnoea is not a disorder of sleep, it’s a respiratory disorder which disrupts sleep
Describe Insomnia
Arousal and sleep mechanisms are simultaneously active
Cannot sleep
Describe Narcolepsy
Periodic overwhelming urge to sleep - but only lasts a few minutes. Recently linked to orexin system.
Describe Cataplexy
When REM-type paralysis occurs during waking
Describe REM Behaviour Disorder
“Acting-out” during REM sleep
Not simply sleep-walking
Can do extreme things such as rape and murder
