Control of Consciousness and Sleep

Question 1

What neuronal components are required for normal consciousness

Answer 1

Cerebral cortex - site where conscious thoughts arise

Reticular formation - circuitry that keeps cortex awak

Question 2

What is the reticular formation

Answer 2

Reticular formation - population of specialised interneurones in the brainstem. Grey matter that runs the full length of the brainstem, receiving numerous inputs that regulates the level of arousal

Has numerous ouputs including thalamus, hypothalamus, basal forebrain nuclei, spinal cord

Question 3

Describe which nuclei the reticular formation sends projections to, i.e. what are they called and what fibres do they send to which places

Answer 3

Basal forebrain nuclei - excitatory cholinergics fibres to cortex

Hypothalamic nuclei - excitatory histaminergic fibres to cortex

Thalamic nuclei - exctiatory glutaminergic fibres to cortex

Also sends projections down the cord to maintian muscle tone

Question 4

What scale is used to determine the conscious level of a patient and what parameters are looked at

Answer 4

Glasgow coma scale is used to determine conscious level of a patient

Looks at eye opening, motor response and verbal response

Question 5

Describe the stages of eye opening in the glasgow coma scale

Answer 5

4 - spontaneous eye opening - normal function

3 - response to speech - slightly diminished function

2 - respnose to pain - imparied cortical function but brainstem preserved

1 - no respnose - severe damage to brainstem +/- cortex

Question 6

Describe the stages of motor response in the glasgow coma scale

Answer 6

6 - obeys commands - normal function

5 - localises to stimuli - diminished higher cortical function

4 - withdraws to pain - response still semi-physiological

3 - flexor response to pain - lesion above level of red nuclei

2 - extensor response to pain - lesion below level of red nuclei

1 - no response to pain - severe damage to brainstem +/- cortex

Question 7

Describe the stages of verbal response in the glasgow coma scale

Answer 7

5 - oriented in time/place - normal function

4 - confused conversation - diminished higher cortical function

3 - inappropriate words - language centres damaged

2 - incomprehensible sounds - cortical damage

1 - no response - severe damage

Question 8

What is used to measure the electrical activity of the brain

Answer 8

Electroencephalogram (EEG) - measure combined electrical activity in neurones in a particular region of the cortex

Good for detecting synchrony and evidence of normal cerebral function

Question 9

Name some functions of sleep

Answer 9

Generally unknown

Energy conservation and body repair

Memory consolidation

Clearance of extracellular debris

Question 10

What are the stages of sleep

Answer 10

Awake with eyes open - beta waves, irregular and fast

Awake with eyes closed - alpha waves, regular and slower

Stage 1 sleep - background alpha and interspaced theta

Stage 2/3 - background of theta and interspaced sleep spindles and K-complexes

Stage 4 - delta waves, regular and slow with high altitude

REM sleep - EEG similar to beta waves

Question 11

What are sleep spindles and what are K-complexes on an EEG

Answer 11

Sleep spindles - high frequency bursts arising from the thalamus

K-complexes - represent emergence of intrinsic rate of the cortex

Question 12

What is the general mechanism by which non-REM sleep occurs

Answer 12

Deactivation of reticular activating system and inhibition of the thalamus

Positive feedback loop between reticular activating system and cortex is inhibited leading to decreased cortical activity

Inhibition of positive feedback is assisted by removal of sensory inputs