Reticular formation and consciousness

Question 1

Define consciousness. (2)

Answer 1

An awareness of external environment and internal states.

Question 2

Define arousal. (2)

Answer 2

Goal-seeking behaviour and avoidance of noxious stimuli, relating to consciousness.

Question 3

Describe the structures needed to maintain consciousness. (4)

Answer 3

The cortex - where conscious thoughts arise. It receives many imputs including from the reticular formation.
The reticular formation - grey matter structure running the length of the brainstem with important roles in bp, breathing, micturition, consciousness.

Question 4

Describe the relationship between the reticular formation and the cortex. (1)

Answer 4

Positive feedback loop.

Question 5

Describe the neurones that set up the loop that maintains consciousness. (8)

Answer 5

Somatosensory neurones imput to the reticular formation.
Cortical imputs also to the reticular formation.
Histaminergic neurones leave the reticular formation, synapse in the hypothalamus and imput to the cortex.
Cholinergic neurones leave the reticular formation, synapse in the basal forebrain nuclei and imput to the cortex.
Glutamatergic neurones leave the reticular formation, synapse in the thalamus and imput to the cortex.

Question 6

Explain why anticholinergics and anti-histamines can cause drowsiness. (2)
Explain why brainstem strokes can reduce consciousness. (2)

Answer 6

Inhibition of cholinergic and histaminergic impulses to the cortex from the reticular formation, meaning consciousness is impaired.
The reticular formation is in the brainstem, so a brainstem stroke will impair the function of the reticular formation.

Question 7

Describe the Glasgow Coma Scale. (18)

Answer 7

Eye opening:
1 - no response, 
2 - pain response,
3 - voice response,
4 - spontaneous 

Verbal response: 
1 - no response, 
2 - incomprehensible sounds 
3 - inappropriate words
4 - confused speech 
5 - oriented to time and place 

Motor response:
1 - no response
2 - extensors response only 
3 - flexor response only 
4 - withdraws from pain
5 - localises to stimuli
6 - obeys commands

Question 8

Describe the classic consciousness sign of an extradural haemorrhage. (2)

Answer 8

Lucid interval.

Following the initial loss of consciousness there is a portion of normal function before deterioration occurs.

Question 9

Describe the functions of an EEG. (1()

Answer 9

Meausres combined activity of neurones in a particular cortical region.

Question 10

Describe the functions of sleep. (4)

Answer 10

Generally unknown.
Energy conservation and repair
Memory consolidation
Clearance fo extracellular debris (eg toxins related to Alzheimer’s)

Question 11

Describe the EEG pattern of an awake person. (3)

Answer 11

Beta waves, irregular, 50Hz.

Question 12

Describethe EEG patten of an awake but eyes closed person. (3)

Answer 12

Alpha waves, regular, 10Hz.

Question 13

Describe the EEG pattens of someone in stage 1 sleep. (4)

Answer 13

Background of alpha waves, theta waves, regular, 5Hz.

Question 14

Describe the EEG pattens of someone in stage 2 or stage 3 sleep. (4)

Answer 14

Background of theta waves, with K-complexes and sleep spangled, 10Hz.

Question 15

Describe the EEG patten of someone in stage 4 sleep. (2)

Answer 15

Delta waves, 1Hz.

Question 16

Describe the EEG patten of someone in REM sleep. Explain why. (4)

Answer 16

Beta waves, irregular, 50Hz.

Dreams are similar to being awake.

Question 17

Explain why stage 2/3 sleep has K-complexes and sleep spindles. (4)

Answer 17

Sleep spindles - thalamic activity - memory consolidation

K-complexes - intrinsic cerebral cortex rate - like the ventricular rate in 3rd degree heart block.

Question 18

Describe non-REM sleep.
Explain why not all sounds wake us up.
(4)

Answer 18

Deactivation of the reticular activating system (no somatosensory inputs) so the cortex and reticular formation are deactivated. Also inhibition of the thalamus.
This is facilitated by the removal of sensory inputs, which is why not all sounds wake us up.

Question 19

Describe REM sleep. (5)

Answer 19

Actively initiated by the pons, but has thalamus inhibition so you stay asleep. Decreased muscle tone through LMN, glycinergic inhibition. Eye movements and cranial nerve function maintained, as well as autonomic functions (eg erection).

Question 20

Describe 3 sleep disorders. (6)

Answer 20

Insomnia - commonly secondary to other psychiatric disorder or physical condition.
Narcolepsy - mutation in the orexin gene.
Sleep apnoea - excess neck fat causes airway compression and frequent waking.

Question 21

Describe 4 disorders of consciousness and their EEG pattens. (12)

Answer 21

Brain death - widespread cortical and brainstem damage. Flat EEG.
Coma - widespread cortical and brainstem damage. Disordered EEG, unresponsive and no sleep-wake cycle.
Persistent vegetable state - widespread cortical damage. Disordered EEG, brainstem reflexes present, sleep-wake cycle present.
Locked-in Syndrome - basilar artery occlusion. Eye movements preserved, but all motor function lost. Normal EEG.