8.2 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 are the 2 aspects required for consciousness?

Answer 3

Cerebral cortex and reticular formation

Question 4

What is formed from the association of these 2 elements?

Answer 4

A positive feedback loop of excitation

Question 5

What do positive feedback loops usually control in the body?

Answer 5

Binary decisions

Question 6

What is the reticular formation?

Answer 6

A population of specialised interneurons in the brainstem

Question 7

What are the inputs of reticular formation?

Answer 7

Somatosensory system

Cerebral cortex

Question 8

What are the 3 major output sites from reticular fibres?

Answer 8

Basal forebrain nuclei
Hypothalamus
Thalamus

Question 9

What neurotransmitter is released from each of the reticular output sites?

Answer 9

Basal forebrain nucleus- Ach
Hypothalamus- Histamine
Thalamus- Glutamate

Question 10

Through that do the reticular fibres project out?

Answer 10

Reticular activating system (RAS)

Question 11

What is the RAS devoted to?

Answer 11

Arousal

Question 12

What is used to assess consciousness?

Answer 12

GCS

Question 13

What are the categories within GCS?

Answer 13

Eye opening
Best motor response
Best verbal response

Question 14

How does each mark correspond to function?

Answer 14

4- Full cortical function
3- Transient disruption to CNS
2- Cortex not working so rely on brainstem reflex
1- Completely unrousable

Question 15

What is used to assess consciousness?

Answer 15

EEG (electroencephalogram)

Question 16

What are the stages of sleep?

Answer 16

Stage 1- light sleep
2
3
4- deepest stage
REM- rapid eye movement sleep

Question 17

Describe EEG show in an awake state?

Answer 17

50 Hz
Beta wave form
Irregular rhythm

Question 18

Describe EEG show in an stage 1 state?

Answer 18

Alpha waves
10 Hz
Increasing synchronisation

Question 19

Describe EEG show in stage 2 and 3?

Answer 19

Background alpha waves
But sleep spindles -from thalamus jerk opening
And K complex

Question 20

Describe EEG show in stage 4

Answer 20

Delta waves
High altitiude
Slow waves

Question 21

Describe EEG show in REM sleep

Answer 21

Same as awake waves= morphology is the same

Beta waves

Question 22

Describe the neural mechanism of sleep

Answer 22

Deactivating the reticular activating system (and hence cortex) and inhibiting the thalamus- slowing down the positive excitatory loop
Assisted by the removal of sensory inuts

Question 23

What is REM sleep also known as?

Answer 23

Paradoxical sleep

Question 24

How is REM sleep is initiated?

Answer 24

By groups of neurones in the pons?

Question 25

Why is REM sleep person difficult to arouse despite beat waves like awake state?

Answer 25

Strong inhibition of the thalamus

Question 26

How does REM sleep prevent movement and acting out of dreams?

Answer 26

Muscle tone in most of the tofu is lost due to descending inhibition of LMN’s by glyvubergic fibres arising from reticular formation and running down the reticulospinal tracts

Question 27

Whichn significant functions are preserves and which are not?

Answer 27

Eye movements and autonomic effects e.g. penile erection are preserved
Loss of thermoregulation

Question 28

What are the functions of sleep?

Answer 28

Enigmatic
Energy conservation and bodily repair
Memory consolidation
Clearance of extracellular debris- alzheimer’s

Question 29

What are some sleep disorders?

Answer 29

Insomnia- secondary to other problem e.g. depression and anxiety
Narcolepsy
Sleep Apnoea

Question 30

What are some disorders of consciousness?

Answer 30

Brain death
Coma
Persistent vegetative state?
Locked in syndrome?