Sleep Mechanisms, Cognition and Memory

Question 1

What is the intrinsic property of the cortex?

Answer 1

Without other influences the activity of the cortex reverts to slow waves and activity becomes synchronised i.e. remove cortex from ascending inputs leads to S-wave sleep

Question 2

What part of the brain controls Arousal?

Answer 2

A major part of the brain which controls arousal is the ascending reticular activating system (ARAS) - part of the reticular formation in the midbrain

Question 3

From where does the ARAS receive input?

Answer 3

All of the major sensory systems and makes connections with the hole of the brain and the spinal cord. Stimulation of the ARAS = arousal from sleep

Question 4

What effect do norepinephrine/noradrenaline and epinephrine/adrenaline have on the ARAS?

Answer 4

The circulating levels in the bloodstream increase arousal

Question 5

Describe the level of activity of the sensory inputs in the neurons of the ARAS when the subject is in the waking state

Answer 5

The sensory input levels remain high

Question 6

What do changes in state of consciousness require in relation to the ARAS?

Answer 6

Changes to occur in the ARAS also. Therefore for sleep to happen, the ARAS has to be inhibited

Question 7

For slepp to happen, what must happen to the ARAS?

Answer 7

It must be inhibited

Question 8

What is responsible for the cycles of S -> D D -> S sleep that occur through the night?

Answer 8

Oscillatory action in two areas of the reticular formation.

Question 9

What two areas in the reticular formation are responsible for the S->D cycles in the night? What type of action causes the cycles?

Answer 9

Gigantocellularis Tegmental Field (GTF)
Local Coerulus

Oscillatory action

Question 10

Describe the GTF

Answer 10

The field consists of very large cells with incredibly long axons and dendrites that make multiple connections throughout the brain. A single GTF cell may contact a million other cells throughout the brain

Question 11

Describe the action of the GTF

Answer 11

It exhibits oscillatory activity, burst of APs appearing just before and during REM sleep. The GTF is the origin of the PGO spikes which give the visual component of dreams.
The GTF action modifies cortical activity directly and through the ARAS. As the GTF stimulates the ARAS, and the ARAS causes wakefulness, this is part of the reason that the sleep changes from synchronised to desynchronised, and this combined with the GTFs direction stimulation of the cortex to produce the S to D part of the sleep cycle

Question 12

What type of neurons make up the GTF?

Answer 12

Cholinergic neurons

Question 13

Give a side effect of cholinesterase inhibitors in relation to the sleep cycle

Answer 13

Because the neurons of the GTF are cholinergic, cholinesterase inhibitors increase the action of acetylcholine by preventing its breakdown, therby stimulating the GTF which then further stimulates the ARAS and the cortex directly. This means that S to D increases and so a side-effect of cholinesterase inhibitors is to increase REM sleep i.e. likely increase nightmares/dreams

Question 14

What is the action of the locus coeruleus?

Answer 14

It releases norepinephrine, acting as an oscillator with the GTF. When the LC cells are active, the GTF cells are not, and this removes the stimulatory action of te GTF on the cortex and the ARAS, providing the D to S part of the sleep cycle. i.e. the LC and GTF both oscillate but produce opposing responses, together forming the alternating D to S and S to D cycles of sleep

Question 15

Describe the circadian rhythm of biological systems

Answer 15

Biological systems show oscillations within roughly a 24hour period

Question 16

What has overall control of the circadian rhythm?

Answer 16

The ‘master-clock’ in the suprachiasmatic nucleus (SCN) of the hypothalamus, just above the optic chiasm

Question 17

What is the suprachiasmatic nucleus (SCN)?

Answer 17

The biological ‘master-clock’ that controls the body’s circadian rhythm. Its neurons exhibit inherent 24 hour cycles

Question 18

What effect does the hypothalamus (SCN specifically) have on the orexin neurons? What effect does this have? What use does orexin have as a treatment?

Answer 18

Inhibition from the hypothalamus turns the orexin neurons off at night. As orexin stimulates wakefulness, it is important for the inhibition to occur at night in order to allow for sleep. Orexin is a possible treatment for insomnia

Question 19

What are some of the influences that develop the 24 hour cycles learned by the neurons of the SCN?

Answer 19

Light/dark cycles - some optic nerve fibres pass to the SCN

Temperature

Question 20

What happens to the circadian sleep cycle if the SCN is destroyed?

Answer 20

Although the specific connections between the SCN and the have not been fully identified, the sleep cycle is destroyed if the SCN is lost

Question 21

What happens to the circadian sleep cycle if people have cues as to light or time?

Answer 21

They gradually increase their day length to 25-30hours

Question 22

What are the health effects of working shifts over a 10 year period?

Answer 22

The incidence of CVS and GI disease increases three-fold

Question 23

What I cognition?

Answer 23

It relates to the highest order of brain function and relates to the behaviour that deals with thought processing

Question 24

What is the fuction of the limbi system with regard to cognitive function and our emotions?

Answer 24

It acts as the link between our higher cognitive function and the ‘more basic’ emotional responses

Question 25

What area of the brain is integral to planning?

Answer 25

The frontal cortex

Question 26

What functions are the limbic system involved with?

Answer 26

Emotion/instinctive behaviour, learning, memory

Question 27

With which areas of the brain does the libic system have strong connections?

Answer 27

The temporal and frontal cortex

Question 28

What is the allocortex?

Answer 28

One of two types of cerebral cortex, the other being the neocortex. The allocortex makes up the core part of the brain and includes the limbic system (functional)

Question 29

Describe the reward functions of the limbic system

Answer 29

The limbic system is important in reward aspects of behaviour. Electrical stimulation o certain areas produce intense feelings of wellbeing, euphoria and sexual arousal = reward areas

Question 30

Describe the punishment functions of the limbic system

Answer 30

Electrical stimulation of certain parts of the limbic system elicits feelings of terror, anger or pain = punishment areas

Question 31

Outline the role of the limbic system in memory

Answer 31

The limbic systems reward/punishment areas lead to motivation. The avoidance of punishment or the pursuit of a reward give the tasks significance. The recall of a memory depends on the significance of the event around the time of storage

Question 32

Define and outline the basis of psychoses

Answer 32

They are a group of disorders which represent endogenous malfunction of the brain e.g. schizophrenia and manic depression. In these conditions the relationship between behaviour and reward and punishment are impaired

Question 33

Define schizophrenia

Answer 33

A dissociation of the ‘cognitive’ side of the brain from the ‘affective/emotional’ side of behaviour

Question 34

What three features characterise the inappropriate behaviours of schizophrenia?

Answer 34

1. Bizarre delusions e.g. of persecution, of having feeling thought and actions controlled by outside forces
2. Auditory hallucinations, hearing voices commenting on their actions
3. Disorders of thought, incoherence, loss of the association between ideas, poverty of speech and loss of emotional resposiveness

Question 35

What is tardive dyskinesia?

Answer 35

A motor manifestation of some anti-schizophrenic medications

Question 36

What feature is shared by the drugs most effective at treating schizophrenia?

Answer 36

They generally interfere with dopamine transmission, mostly by blocking DA receptors

Question 37

What is the major side effect of most anti-schizophrenic drugs?

Answer 37

They cause Parkinsonism

Question 38

What can be a side effect of drugs that enhance DA action?

Answer 38

Causing schizophrenic-like psychotic disorders e.g. amphetamine - increases DA release, cocaine - decreases DA breakdown (and L-DOPA)