Session 8: The Reticular Formation - Control of Consciousness

Question 1

Define arousal.

Answer 1

The emotional state associated with some kind of goal or avoidance of something noxious.

Question 2

Define consciousness.

Answer 2

Something to do with awareness of both external world and internal states.

Question 3

What two basic ingredients are required for consciousness?

Answer 3

The cerebral cortex and the reticular formation.

Question 4

Explain the communication between the cerebral cortex and the reticular formation.

Answer 4

It is a positive feedback loop where the cortex excites the reticular formation and the reticular formation excites the cortex.

Question 5

What is the reticular formation?

Answer 5

A population of specialised interneurones in the brainstem.

Question 6

Input to the reticular formation.

Answer 6

Sensory system

Cortex

Question 7

Outputs from the reticular formation.

Answer 7

Thalamus

Hypothalamus

Basal forebrain nuclei

Spinal cord

Question 8

Explain the basal forebrain nuclei pathway.

Answer 8

Information goes from the reticular formation in the lateral brainstem up to the basal forebrain nuclei.

Another neuron then goes to the cortex and synapse. It then uses ACh as an excitatory neurotransmitter.

Question 9

Explain the hypothalamic pathway.

Answer 9

RF -> hypothalamus

Then to cortex and release histamine leading to excitation.

Question 10

Explain the thalamic pathway.

Answer 10

RF -> Thalamus

Thalamus -> Cortex and releases glutamate leading to excitation.

Question 11

What is a side effect of anticholinergics and antihistamines?

Answer 11

Drowsiness as they can inhibit the excitation of the cortex.

Question 12

How do you assess consciousness?

Answer 12

Glasgow coma scale.

Electroencephalogram (EEG)

Question 13

What is assessed in GCS?

Answer 13

Eye opening

Motor response

Verbal response

Question 14

What is the highest and lowest score on GCS?

Answer 14

15-3

Question 15

Levels of eye opening.

Answer 15

4 - Spontaneous (full cortical)

3 - Response to speech (impaired cortical)

2 - Response to pain (no cortical)

1 - No response (brainstem dysfunction)

Question 16

Levels of motor response

Answer 16

6 - Obeys command (full cortical)

5 - Localises motor response (cortical damage)

4 - Withdraw from the pain ellicited (only brainstem working)

3 - Flexor response to pain (decorticate lesion (above red nucleus))

2 - Extension response to pain (illogical) (decerebrate lesion (below red nucleus))

1 - No response

Question 17

Levels of verbal response

Answer 17

5 - Oriented (What year is this - followed by correct answer)

4 - Confused conversation (will give wrong year but understood question) Cortical damage

3 - Inappropriate words (‘‘yesterday’’, ‘‘mother’’) Severe cortical damage

2 - Incomprehensible sounds like groans or screaming. Mediated by brainstem centers - subcortically

1 - No response

Question 18

What does an EEG do?

Answer 18

Measures the combined activity of thousands of neurones in a given part of the cortex to a very high temporal resolution but very poor spatial resolution.

Question 19

If the neurones gets deprived of sensory input (external stimulus), what will happen to the pattern of the firing of neurones.

Answer 19

They will start to fire in sync.

Question 20

Give an example when neurones fire in sync.

Answer 20

During sleep

Question 21

How many cycles of sleep does a person typically pass through in a night?

Answer 21

6

Question 22

Stages of sleep.

Answer 22

Awake

Eyes closed

Stage 1

Stage 2/3

Stage 4

REM sleep

Question 23

Going down the stages of sleep, how does the EEG pattern change?

Answer 23

A decrease in frequency and an increase in amplitude as the neurones starts to synchronise.

Question 24

What stop the neurones from going into synchrony?

Answer 24

External stimulus

Question 25

EEG differences between being awake and in REM

Answer 25

Indistinguishable

Question 26

Neural mechanism of sleep

Answer 26

Deactivation of the reticular system -> deactivation of the cortex + inhibition of the thalamus.

This is because there is inhibition of the +ve feedback loop leading to decreased cortical activity.

This deactivation is due to removal of sensory inputs which send positive signals to the feedback loop.

Question 27

Where in the brain is REM initiated?

Answer 27

By groups of neurones in the pons

Question 28

Why is it difficult to rouse a person in REM sleep?

Answer 28

Strong inhibition of the thalamus

Question 29

Motor effects of REM sleep.

Answer 29

Muscle tone is lost due to descending inhibition of LMNs by glycinergic fibres.

They arise from the reticular formation and run down the reticulospinal tracts.

It is thought that muscles are inhibited in REM sleep in order to not act out your dreams (which happen in REM sleep)

Question 30

What is still preserved in REM sleep?

Answer 30

Eye movements and some other cranial nerve functions

Question 31

What is nocturna bruxism?

Answer 31

Grinding of teeth during night

Question 32

Autonomic effects of REM sleep

Answer 32

Penile erecion

Loss of thermoregulation

Question 33

What happens if you don’t get REM sleep?

Answer 33

It is essential for life.

You will die.

Question 34

Functions of sleep.

Answer 34

Energy conservation/repair?

Memory consolidation?

Clearance of extracellular debris?

Question 35

Disorders of sleep

Answer 35

Insomnia

Narcolepsy

Sleep apnoea

Question 36

Explain insomnia

Answer 36

Rarely primary and alsmost always secondarily to either anxiety or depression.

(Trouble sleeping)

Question 37

Explain narcolepsy

Answer 37

Rare condition despite what people think.

Can be caused by a mutation in the orexin gene where orexin is involved in sleep.

Question 38

Explain sleep apnoea.

Answer 38

Constant tiredness because you keep waking up at night (can be like 70 times during a night)

This is common and often caused by excessive neck fat leading to compression of airways and frequent waking.

This leads to drowsiness during the day.