Consciousness

Question 1

Compare Consciousness and Arousal

Answer 1

Consciousness: Awareness of external environment and internal states

Arousal: Emotional state associated with goal-seeking behaviour and avoidance of noxious stimuli

Question 2

Describe the 2 neural components that to be connected to each other and function normally in order to have Consciousness

Answer 2

Cerebral cortex;

• Where conscious thoughts arise
• Receives many inputs including from Reticular Formation

Reticular formation (especially the reticular activating system);

• Keeps cortex ‘awake’
• Receives many inputs including from Cortex and Sensory Systems

Question 3

Describe the connection between the Reticular Formation and the Cerebral Cortex

Answer 3

Connected by Reciprocal Excitatory Projections, forming a positive feedback loop

(Positive feedback loops are seen where there is a binary outcome)

Question 4

What is the Reticular formation?

List 4 output locations

Answer 4

A population of specialised interneurones in the brainstem

• Thalamus-> Cortex
• Hypothalamus-> Cortex
• Basal forebrain nuclei-> Cortex
• Spinal cord (muscle tone regulation)

Question 5

What is the Reticular Activating System?

Answer 5

Part of the reticular formation devoted to arousal

Neurones that ascend to the cortex to maintain cortical activity

Question 6

Output from Reticular Formation occurs via 3 major relay nuclei

Compare them

Answer 6

Basal Forebrain Nuclei: Send excitatory cholinergic fibres to cortex

Hypothalamus: Sends excitatory histaminergic fibres to cortex

Thalamus: Sends excitatory glutamatergic fibres to cortex

Question 7

What tool is most commonly used to asses consciousness?

What are the 3 components this looks at?

Answer 7

Glasgow Coma Scale (GCS)

• Best response in eye opening
• Best motor response
• Best verbal response

Question 8

Other than the GCS, an EEG can be used to assess consciousness

Describe what an Electroencephalogram measures
Describe the resolution quality

Answer 8

Measured combined activity of thousands of neurones in a particular region of the cortex

Good temporal resolution (can see changes across milliseconds)
Low spatial resolution (not good for localising lesions)

Question 9

What is Neuronal Synchrony?

Answer 9

When neurones in the brain fire synchronously, such as when deprived of sensory input

Question 10

List 2 processes that an EEG is good for detecting

Answer 10

• Normal cerebral function

- Neuronal synchrony

Question 11

What are the stages of sleep?

Answer 11

• Stages 1-4

- REM sleep

Question 12

What happens in 1 sleep cycle?

How many sleep cycles do we usually go through a night?

Answer 12

We enter progressively deeper stages of sleep, then change to REM sleep

6

(Stage 4 is the deepest stage of non-REM sleep)

Question 13

When awake, why do you see an EEG become more regular when your eyes close?

Answer 13

No visual sensory input leads to Neuronal Synchrony

Question 14

Describe the EEG pattern in Stage 1 of sleep

Answer 14

Background Alpha waves + interspersed Theta waves

Question 15

Describe the EEG pattern in Stage 2/3 of sleep

Answer 15

• Background Theta waves
• Interspersed Sleep Spindles and K-Complexes

(Sleep spindles: High frequency)
(KCs: Low frequency, high amplitude)

Question 16

What are Sleep Spindles and K-Complexes

Answer 16

Sleep spindles: High frequency bursts from thalamus

K-Complexes: Emergence of ‘Intrinsic rate’ of cortex

Question 18

Describe the EEG pattern in REM Sleep

Dreaming occurs in this stage

Answer 18

Similar to Beta wave pattern when awake

Question 19

Describe the neural mechanism of Non-REM Sleep

Answer 19

• Removal of sensory inputs, leads to inhibition of RAS-Cortex Positive Feedback Loop
• Leads to Deactivation of Reticular Activating System, leading to Inhibition of Thalamus

Question 20

Describe the mechanism leading to REM sleep

Answer 20

• Initiated by neurones in the Pons (appears to be an active process)
• Strong inhibition of thalamus (so difficult to wake patient up)

Question 21

Describe the effect of REM sleep on Muscle Tone

Answer 21

• Inhibition of LMNs by glycinergic fibres coming from Reticular Formation

(To stop us acting out dreams. Sleepwalking is a disorder where this process doesn’t work properly)

Question 22

Describe the effect of REM Sleep on Eye movements + other cranial nerve functions

Answer 22

Some can be preserved (Can lead to teeth grinding)

Question 23

List 2 autonomic effects that work in REM sleep

Answer 23

• Penile erection

- Thermoregulation

Question 24

What does long term deprivation of REM sleep lead to?

Answer 24

Death

Question 25

List 3 sleep disorders (not including sleepwalking)

Answer 25

• Insomnia
• Narcolepsy
• Sleep Apnoea

Question 26

What commonly causes Insomnia?

Answer 26

An underlying psychiatric disorder, such as anxiety or depression

(This is Secondary Insomnia)

Question 27

What may cause Narcolepsy?

Answer 27

• Mutations in Orexin/ Hypocretin gene

Orexin a transmitter that couples light perception to hypothalamus

Question 28

What causes Sleep Apnoea?

Causes excessive daytime sleepiness

Answer 28

• Often caused by excessive neck fat

- Compression of airways during sleep-> Frequent waking

Question 29

List and describe 4 disorders of consciousness

Answer 29

• Brain death (widespread cortical and brainstem damage, flat EEG)
• Coma (“” with various EEG patterns, sleep wave cycle undetectable)
• PVS (widespread cortical damage, various EEG patterns, sleep wave cycle detectable, with spontaneous eye opening)
• Locked in Syndrome (Can be caused by basilar/pontine artery occlusion, eye movements can be preserved, loss of somatic motor functions from the Pons down)

Question 30

What neurotransmitter is used in the synapse between RAS fibres and the Thalamus, Hypothalamus and Basal Forebrain Nuclei

Answer 30

ACh

Question 31

Describe the EEG pattern in Stage 4 of sleep

Answer 31

Delta waves (Low frequency, high amplitude)

K complexes in Stage 2/3 are a prelude to delta waves