Consciousness

Question 1

What is consciousness?

Answer 1

Related to awareness of external environment and internal states.

Arousal is a related concept which is associated with goal-seeking behaviour and avoidance of noxious stimuli.

Question 2

What two neuronal components are required to be functioning normally for consciousness?

Answer 2

Cerebral cortex - site where consciousness thought to arise.

Reticular formation - keeps the cortex awake.

Question 3

What connects the cortex and the reticular formation?

Answer 3

Cortex and the reticular formation are connected by reciprocal excitatory projections, forming positive feedback loop.

(positive feedback seen when there is a binary outcome)

Question 4

What are the three main relay nuclei from the reticular formation?

Answer 4

Reticular formation sends cholinergic projections to:

Basal forebrain nuclei send excitatory cholinergic fibres to cortex

Hypothalamus sends excitatory histaminergic fibres to the cortex

Thalamus sends excitatory glutamatergic fibres to the cortex.

The reticular formation also sends projections down the cord, responsible for maintaining muscle tone.

Question 5

How do you assess consciousness?

Answer 5

Use GCS or AVPU scale.

Question 6

What are the three components assessed in GCS?

Answer 6

Eye opening (1-4)

Motor response (1-6)

Verbal response (1-5)

Question 7

What is an electroencephalogram?

Answer 7

It measures the combined activity of thousands of neurones in a particular region of cortex.

High temporal resolution, low spatial resolution.

Good for detecting neuronal synchrony (a phenomenon which occurs commonly in the brain during both physiological and pathological processes such as sleep and epilepsy), and evidence of normal cerebral function.

Question 8

What are the functions of sleep?

Answer 8

Generally unknown

Energy conservation and repair?

Memory consolidation?

Clearance of extracellular debris?

‘Resetting’ of the CNS?

Question 9

How many stages of sleep are there?

Answer 9

Four major stages and REM sleep

Question 10

How many cycles of sleep do you pass through per night?

Answer 10

6

Question 11

What EEG pattern is shown if you’re awake with your eyes open?

Answer 11

Beta waves - irregular, 50Hz

Question 12

What EEG pattern is shown if you’re awake with your eyes closed?

Answer 12

Alpha waves - regular 10Hz

Question 13

What EEG pattern is shown in stage 1 sleep?

Answer 13

Background of alpha and interspersed theta waves (theta at around 5Hz, regular)

Question 14

What EEG pattern is shown in stage 2/3 sleep?

Answer 14

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

Question 15

What are sleep spindles?

Answer 15

Sleep spindles are high frequency bursts arising from the thalamus.

Question 16

What do K complexes represent?

Answer 16

K-complexes represent the emergence of the ‘intrinsic rate’ of the cortex.

Question 17

What EEG pattern is shown in stage 4 sleep?

Answer 17

Delta waves - regular, 1Hz

These are related the K-complexes seen in stages 2/3.

Question 18

What EEG pattern issues in REM sleep?

Answer 18

AN EEG similar to beta waves (awake with eyes open) but difficult to arouse due to strong thalamic inhibition.

Question 19

What activates REM sleep?

Answer 19

It is activated by neurones in the pons (initiation appears to be an active process).

Question 20

What functions are seen / not seen in REM sleep?

Answer 20

Decreased muscle tone due to glycinergic inhibition of lower motor neurones.

Eye movement and some other cranial nerve functions preserved (e.g. teeth grinding).

Autonomic effects are seen (e.g. erections and loss of thermoregulation).

REM sleep is essential for life.

Question 21

What is insomnia most commonly caused by?

Answer 21

Commonly caused by underlying psychiatric disorder as opposed to primary insomnia.

Question 22

What causes narcolepsy?

Answer 22

Some cases are caused by a mutation in the orexin gene.

Orexin is a peptide transmitter involved in sleep.

Question 23

What causes sleep apnoea?

Answer 23

Common condition often used by excess neck fat leading to compression of airways during sleep and frequent waking.

It causes excessive daytime sleepiness.