Consciousness

Question 1

What is consciousness?

Answer 1

• Related to awareness of external and internal states
• Arousal is a related concept which is associated with goal-seeking behaviour and avoidance of noxious stimuli

Question 2

Which two neural components are required for consciousness?

Answer 2

• Cerebral cortex
• Reticular formation

Question 3

What is the function of the cerebral cortex in consciousness?

Answer 3

• The site where conscious thoughts arise
• Receives many inputs, including from the reticular formation

Question 4

What is the function of the reticular formation in consciousness?

Answer 4

• This is the circuitry that keeps the cortex awake
• Receives many inputs from the cortex and sensory systems

Question 5

How do the cortex and reticular formation work together?

Answer 5

• Connected by reciprocal excitatory projections, forming a positive feedback loop
• Positive feedback loops are seen where there is a binary outcome

Question 6

What are the outputs from the reticular formation to the cortex?

Answer 6

• Occurs via three major relay nuclei
• Reticular formation sends cholinergic (excitatory) projections to these relays

Question 7

What are the different major relay nuclei of the reticular formation?

Answer 7

• Basal forebrain nuclei
• Hypothalamus
• Thalamus

Question 8

What do the basal forebrain nuclei do?

Answer 8

• Send excitatory cholinergic fibres to cortex
• Think sedative side effects of anticholinergics

Question 9

What does the hypothalamus do?

Answer 9

• Send excitatory histaminergic fibres to the cortex
• Think sedative side effects of antihistamines

Question 10

What does the thalamus do?

Answer 10

• Sends excitatory glutamatergic fibres to the cortex

Question 11

What is the motor function of the reticular formation?

Answer 11

• Sends projections down the cord, responsible for maintaining muscle tone

Question 12

How is consciousness clinically assessed?

Answer 12

• GCS

Question 13

What are the components of the GCS?

Answer 13

• Eye opening
• Motor response
• Verbal response

Question 14

How is eye opening assessed in the GCS?

Answer 14

• Spontaneous eye opening suggests normal cortical and brainstem function
• Response to speech suggests slightly diminished cortical function but still functioning brainstem
• Response to pain suggests impaired cortical function but brainstem preserved so that reflex opening can occur
• No response suggests severe damage to brainstem +/- cortex

Question 15

How is motor response assessed in the GCS?

Answer 15

• Obeys commands (6)
• Localises to stimuli (5)
• Withdraws to pain (4)
• Flexor response to pain (3)
• Extensor response to pain suggests a lesion below the red nuclei (not physiological at all)
• No response to pain suggests severe damage to brainstem +/- cortex

Question 16

What does a patient obeying a motor command suggest?

Answer 16

• Normal function with working connections from auditory system to brainstem/cord

Question 17

What does a patient localising to stimuli suggest?

Answer 17

• Diminished higher cortical function but still connections working from sensory to motor cortex

Question 18

What does a patient withdrawing to pain suggest?

Answer 18

• There is still a physiological reflex response to stimuli

Question 19

What does a patient flexing in response to pain suggest?

Answer 19

• Suggests a lesion above the level of the red nuclei (semi-physiological)

Question 20

What does a patient extending in response to pain suggest?

Answer 20

• Severe damage to the brainstem +/- cortex

Question 21

How is verbal response assessed by the GCS?

Answer 21

• Oriented in time/place (5) - normal cortical function
• Confused conversation (4) - diminished higher cortical function but language centres are still functioning adequately
• Inappropriate words (3) - language centres have been damaged
• Incomprehensible sounds (2) - cortical damage with brainstem mediated groans
• No response (1) - severe damage to brainstem +/- cortex

Question 22

What does the electroencephalogram measure?

Answer 22

• The combined activity of thousands of neurones in a particular region of the cortex
• High temporal resolution, low spatial resolution

Question 23

What is the electroencephalogram good for?

Answer 23

• Detecting neuronal synchrony and evidence of normal cerebral function

Question 24

What is neuronal synchrony?

Answer 24

• A phenomenon which occurs commonly in the brain during both physiological and pathological processes such as sleep and epilepsy

Question 25

What are the functions of sleep?

Answer 25

- Generally unknown - Energy conservation/repair - Memory consolidation - Clearance of extracellular debris - Resetting of the CNS

Question 26

How many sleep cycles do we typically pass through each night?

Answer 26

- 6

Question 27

What are the stages of sleep?

Answer 27

- 4 major stages and REM sleep

Question 28

What happens on an EEG when a person is awake with their eyes open?

Answer 28

- Beta waves - irregular, 50 Hz

Question 29

What happens on an EEG when a person is awake with their eyes closed?

Answer 29

- Alpha waves - regular, 10 Hz

Question 30

What happens on an EEG when a person is in stage 1 sleep?

Answer 30

- Background of alpha and interspersed theta waves - At around 5 Hz

Question 31

What happens on an EEG when a person is in stage 2/3 sleep?

Answer 31

- Background of theta and interspersed sleep spindles and k-complexes

Question 32

What are sleep spindles?

Answer 32

- High frequency bursts arising from the thalamus

Question 33

What are k complexes?

Answer 33

- Represent the emergence of the intrinsic rate of the cortex

Question 34

What happens on an EEG when a person is in stage 4 sleep?

Answer 34

- Delta waves - regular 1 Hz - Related to k-complexes seen in stages 2/3

Question 35

What happens on an EEG when a person is in REM sleep?

Answer 35

- Initiated by neurones in the pons - EEG is similar to when person is awake with eyes open

Question 36

What happens to the body during REM sleep?

Answer 36

- Difficult to rouse due to strong thalamic inhibition - Decreased muscle tone due to glycinergic inhibition of LMNs - Eye movements and some other cranial nerve functions can be preserved - Autonomic effects are seen - Essential for life

Question 37

What are some different types of sleep disorder?

Answer 37

- Insomnia - commonly caused by underlying psychiatric disorder as opposed to primary insomnia - Narcolepsy - rare disorder - Sleep apnoea - causes excessive daytime sleepiness

Question 38

What causes narcolepsy?

Answer 38

- Some cases are caused by mutations in the orexin gene - Orexin is a peptide

Question 39

What causes sleep apnoea?

Answer 39

- Excess neck fat leading to compression of airways during sleep and frequent waking