Week B1 Memory & Sleep II

Question 1

What are dreams?

Answer 1

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

Question 2

What is the sequence of REM/NREM sleep throughout the night?

Answer 2

With each cycle, REM sleep gets longer

Question 3

What is the best theory for the function of sleep?

Answer 3

Memory consolidation: REM sleep appears to be a replay of the days activities, occuring whilst the cortex is disconnected

Question 4

How does REM sleep change as we age?

Answer 4

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)

Question 5

What is Instructional Replay?

Answer 5

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.

Question 6

How does consolidation occur during sleep?

Answer 6

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.

Question 7

Define Circadian Rhythm

Answer 7

Major sleep/wake cycle that runs at ~24-25 hours

Question 8

Define Zeitgebers

Answer 8

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.

Question 9

Define Ultradian Rhythm

Answer 9

90-minute cycle/rhythm that occurs during sleep and wakefulness

Generated by the medulla
A time-keeping mechanism operating on the cellular level

Question 10

Describe the neurological drive of wakefulness

• Structures involved
• Key neurotransmitters involved

Answer 10

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)

Question 11

Describe the Orexin System

& where is originates

Answer 11

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

Question 12

Describe the neurological control/inducement of sleep

Answer 12

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

Question 13

How is light used as a zeitgeber for the circadian rhythm?

Answer 13

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

Question 14

What are the functions of the Suprachiasmic Nucleus (SCN)?

Location?

Answer 14

“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***

Question 15

Describe Circadian Temperature Variation

Answer 15

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)

Question 16

Functions of the Dorsomedial Hypothalamus

Answer 16

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

Question 17

What regulates the stages of sleep?

Answer 17

Regions of the brainstem and midbrain.

Geting by Thalamic Nuclei prevents stimuli from reaching the cortex

Question 18

What regulates REM sleep?

Answer 18

Pontine Nuclei
Send cholinergic neurons to the Thalamus, and projections to inhibit skeletal muscle movements (aside from respiratory muscles, duh)

Question 19

Describe the relationship between sleep and metabolism, and the metabolic repercussions of sleep deprivation

Answer 19

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

Question 20

List the major disorders of sleep:

Answer 20

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

Question 21

Describe Insomnia

Answer 21

Arousal and sleep mechanisms are simultaneously active

Cannot sleep

Question 22

Describe Narcolepsy

Answer 22

Periodic overwhelming urge to sleep - but only lasts a few minutes. Recently linked to orexin system.

Question 23

Describe Cataplexy

Answer 23

When REM-type paralysis occurs during waking

Question 24

Describe REM Behaviour Disorder

Answer 24

“Acting-out” during REM sleep
Not simply sleep-walking
Can do extreme things such as rape and murder

Question 25

Describe Slow Wave Disorders

Answer 25

The individual can interact with others, but isn’t conscious - includes night terrors, bed wetting,e tc.

Question 26

Visual Pathway that affects circadian rhythm. How does it do this?

Answer 26

Melanopsin pathway: info from retina to suprachiasmic nucleus in Anterior Periventricular Zone of Hypothalamus -> “master clock” nucleus -> In this way, light acts as a Zeitgeber to synchronise circadian rhythm (24-25 hour cycle) with external environment - namely day/night time