7 - Wakefulness & Sleep

Question 1

Endogenous circadian rhythms

Answer 1

Internal mechanisms that operate on an approx 24 hour cycle
All animals produce endogenous circadian rhythms
(Endogenous means ‘generated from within’)

Question 2

Circadian rhythms are assessed using:

Answer 2

Physiological measures: body temperature, saliva samples

Behavioural measures: timing of sleep, meals, etc.

Question 3

Infradian rhythm

Answer 3

Biological rhythm lasting longer than a circadian rhythm eg. Menstrual cycle

Question 4

Circannual rhythm

Answer 4

Biological rhythm lasting lasting one year eg. Hibernation, season affect disorder

Question 5

Ultradian rhythm

Answer 5

Biological rhythm lasting shorter than a circadian rhythm eg. Stages of sleep, hunger fluctuations

Question 6

Circadian rhythm acts as a biological clock

Answer 6

Ensures biological processes occur in phase with the outside world.
Generates a rhythm slightly longer than 24 hours when it has no external cue to set it eg. Pilots

Question 7

Zeitgber

Answer 7

Refers to the stimulus that resets the circadian rhythm.
Primary zeitgeber for humans is sunlight (also darkness) (thus we can manipulate these).
But secondary zeitgebers are also used, including exercise and social interaction.

Question 8

The Superchiasmatic Nucleus

Answer 8

The main control centre of the circadian rhythms of sleep and temperature.
Located above the optic chosen and part of the hypothalamus.
Damage to the SCN results in less consistent circadian rhythms. (Initial change but no lasting damage so not totally in control)

Question 9

Retinohypothalamic Path

Answer 9

Light resets the SCN via a small branch of the optic nerve known as the retinohypothalamic path (special oath of ganglion cells) (Travels directly from the retina to the SCN)
Special ganglion cells that have their own photopigment (melanopsin) form this path.
Responds to mass changes in light, not details ie is it day or night?

Question 10

Proteins and the SCN

Answer 10

SCN cells make 2 proteins: CLOCK and CYCLE
They bind to DNA in the nucleus of SCN cells to transcribe the proteins, PER and TIM.
PER and TIM proteins inhibit the expression of CLOCK and CYCLE genes. (this slows the production of PER and TIM)
PER and TIM proteins are slowly broken down, entire process takes approx 24 hrs.

Question 11

Melatonin

Answer 11

The SCN regulates the pineal gland.

The pineal gland secretes melatonin, a hormone that increases sleepiness.

Question 12

Stages of Sleep

Answer 12

EEG has allowed researchers to study the stages of sleep - compare brain activity at different times during sleep.
Combining measures of EEG, heart rate, respiration rate, blood oxygen levels, eye and leg movements has helped uncover characteristics of each stage.

Question 13

R.E.M. Sleep (paradoxical sleep)

Answer 13

Rapid eye movement sleep.
Describes periods characterised by rapid eye movements during sleep.
Also known as paradoxical sleep:
Deep sleep - postural muscles of the body are more relaxed than other stages.
Light sleep - EEG waves are irregular, low voltage, and fast.
Dreaming occurs during R.E.M. sleep

Question 14

Pontomesencephalon

Answer 14

Part of the reticular formation.
Receive input from many sensory systems.
Maintains arousal during wakefulness and stimulation during sleep wakes a person, already awake increases alertness.

Question 15

Locus coerulus

Answer 15

Small structure in the pons.
Releases norepinephrine.
Increases the activity of the most active neurons and decreases activity of less active neurons = enhanced attention to important information and enhance memory.

Question 16

Posterior hypothalamus

Answer 16

Releases histamine (has excitatory effects) to keep us awake/increases arousal

Question 17

Ventro-lateral hypothalamus

Answer 17

Receives information from histamine channels, release orexin - enhances wakefulness.

Question 18

Brain mechanisms of sleep

Answer 18

Inhibition of reticular formation = less sensory information
Inhibition of thalamic nuclei decreases sensory input being projected to cortical regions
GABA: inhibitory neurotransmitter released during sleep. Interferes with the spread of information.

Question 19

Brain function during R.E.M. Sleep

Answer 19

Activity increases in the pons.
Activity decreases in the primary visual cortex, the motor cortex, and the dorsolateral prefrontal cortex.

Waves of high-amplitude neural activity (PGO waves) pass through the pons, lateral geniculate and occipital cortex.
Function of PGO waves is unclear (maybe copy of motor waves?)
Also related to saccadic eye movement while awake.

Question 20

Sleep Apnea

Answer 20

A sleep disorder characterised by the inability to breathe while sleeping.
Obstructive apnea: relaxation of the chest, diaphragm, throat (common in obese people)
Central apnea: malfunctioning of breathing reflex response mediated by brain stem structures.

Question 21

Narcolepsy

Answer 21

A sleep disorder characterised by frequent periods of sleepiness.
Gradual or sudden attacks of sleepiness.
Occasional cataplexy: muscle weakness triggered by strong emotions.
Sleep paralysis: inability to move while falling asleep or waking up.
Hypnagogic hallucinations: dreamlike experiences during sleep onset.

Question 22

Periodic limb movement

Answer 22

The repeated involuntary movement of the legs and sometimes the arms while sleeping.
Legs kick once every 20-30 seconds for periods of minutes to hours.
Usually occurs during NREM sleep.
Distinct from restless leg syndrome.
Precedence unclear.

Question 23

GABA role in sleep

Answer 23

Inhibitory neurotransmitter released during sleep.
Interferes with the spread of information.
Produces excitation during the day and inhibition during the night in the SCN.

Question 24

Night terrors and sleepwalking

Answer 24

Night terrors are experiences of intense anxiety from which a person awakens screaming in terror (associated with autonomic hyperactivity).
Night terrors and sleep walking are tightly related.both considered to occur exclusively in NREM, especially slow wave sleep/deep sleep.

Question 25

Functions of sleep (general)

Answer 25

Resting muscles
Recharging
Reorganising the brain
General period of recovery etc. 
Considered most important after a hard day to restore supply and prepare for the following day.

Question 26

Three main functions of sleep

Answer 26

1. Energy conservation
2. Body restoration
3. Memory consolidation

Question 27

Energy conservation

Answer 27

Energy use is reduced when we sleep
Energy is conserved for periods of greatest efficiency. 
Stage 3 sleep is characterised by:
Muscle relaxation
Decreases heart rate
Reduced blood pressure
Reduced body temperature (maintaining higher body temp uses a lot of energy)
Slowed respiration

Question 28

Body restoration

Answer 28

One function of sleep is the rebuild or replenish deprecated materials (e.g. proteins) used while awake.
Elevated release of growth hormone during sleep - particularly slow wave sleep.
Increased activity of glial cells during sleep:
Results in removal of waste products throughout the brain
Inadequate sleep may elevate risk of alzheimers due to build-up of waste products

Question 29

Memory consolidation

Answer 29

Sleep aids in memory consolidation.
Sleep after a learning period results in increased performance on a memory test.
Patterns of neural activity occurring during rehearsal/learning are replicated during sleep.
Sleep deprivation is associated with greater susceptibility to the formation of false memories.

Question 30

Functions of R.E.M. sleep

Answer 30

Exact function of R.E.M. Sleep is unclear.
Hard to study R.E.M. Sleep due to methodologies.
During R.E.M.:
The brain may discard useless connections
Learned motor skills may be consolidated
High prevalence of dreams
Seems to be no advert effects from having no R.E.M. Sleep, so may not have any benefit.
Maurice - function of R.E.M. Is to provide sufficient oxygen to the corneas

Question 31

Biological perspectives of dreaming

Answer 31

The activation-synthesis hypothesis

The clinico-anatomical hypothesis

Question 32

Activation-Synethesis Hypothesis

Answer 32

Brain trying to make sense of spontaneous activity in the pons.
Dreams begin with spontaneous activity in the pons, which activates many parts of the cortex.
The cortex synthesises a story from the pattern of activation.
Normal sensory information is sometimes integrated, but usually not.

Question 33

Clinico-Anatomical Hypothesis

Answer 33

Certain brain areas are active and other not, so brain tries to makes sense of this.
Activity is high:
In the inferior part of the parietal cortex, an area important for visual-spatial perception.
In the hypothalamus and amygdala, which accounts for the emotional and motivation content of dreams.
Activity is low:
In the primary visual cortex, auditory cortex and primary motor cortex.