8b.) Consciousness

Question 1

What is consciousness?

Answer 1

• Hard to define
• Related to awareness of external environment and internal states

Question 2

What is arousal?

Answer 2

Emotional state associated with some kind of goal seeking behaviour or avoidance of noxious stimuli

Question 3

Consciousness requiers two neural components to be functioning normally and connected to each other; what are these two components?

Answer 3

Cerebral cortex

Reticular formation

Question 4

Where do conscious thoughts arise?

Answer 4

Cerebral cortex

Question 5

What is the role of the reticular formation

Answer 5

Circuitry that keeps cortex awake (particularly the reticular activating system in the brainstem)

Question 6

Where does reticular formation receive inputs from?

Answer 6

Cerebral cortex and sensory systems

Question 7

What fibres connect the cortex and reticular formation?

Answer 7

Reciprocal excitatory projection fibres connect the cortex & reticular formation creating a positive feedback loop

Question 8

What type of feedback loop is seen between the cortex and reticular formation?

Answer 8

Positive feedback loop

Question 9

When are positive feedback loops seen?

Answer 9

When there is a binary outcome e.g. sleep/awake, ovulating/not ovulating, clotting/not clotting etc…

Question 10

Outputs from the reticular formation, to the cortex, occur via three major relay nuclei:

• State the neurotransmitter which the reticular formation uses to communicate with each of the relay nuclie
• State the relay nuclei and also state the transmitter used

Answer 10

Reticular formation sends cholinergic (excitatory) projections to the following relay nuclei:

• Basal forebrain nuclei: send excitatory cholinergic fibres to cortex (ACh)
• Hypothalamus: send excitatory histaminergic fibres to cortex (Histamine)
• Thalamus: sends excitatory glutamatergic fibres to cortex (glutamate)

Question 11

Alongside projecting to the cortex via 3 relay nuclei, does the reticular formation project anywhere else?

Answer 11

Yes, it also sends projections down the cord (responsible for maintaining muscle tone)

Question 12

Summarise the outputs from the reticular formation

Answer 12

• Excitatory to cortex
  
  • Cholinergic excitatory fibres to relay nuclei
  • Relay nuclei use different neurotransmitters to excite cortex
• Also has excitatory fibres projection fibres down spinal cord to maintain muscle tone

Question 13

What is the reticular formation?

Answer 13

Population of specialised interneurones in brainstem which receives numerous inputs from sensory system & cortex- which regulates arousal. Has widespread outputs to thalamus, hypothalamus, basal forebrain nuclei (which then project to cortex)and spinal cord.

Question 14

Clinically, what is used to assess consciousness?

Answer 14

GCS score

Question 15

Describe the 3 components of the GCS (Glasgow Coma Scale) and state the scores which can be given for each

Answer 15

• Eye opening (scored 1-4)
• Motor response (scored 1-6)
• Verbal response (scored 1-5)

Question 16

Eye opening is one of the components assessed in the GCS score; for each score that can be given suggest what it indicates

Answer 16

Eye opening scored 1-4:

• 4= spontaneous eye opening- suggests normal cortical and brainstem function
• 3= response to speech- suggests slightly diminished cortical function but still functioning brainstem
• 2= response to pain- suggests impaired cortical function but brainstem preserved so that reflex opening can occur
• 1= no response- suggests severe damge to brainstem +/- cortex

Question 17

Motor response is one of the components assessed in the GCS score; for each score that can be given suggest what it indicates

Answer 17

Motor response is scored 6-1:

• 6= obeys commands- suggests normal function with working connections from auditory system to brainstem/cord
• 5= localises to stimuli- suggests diminished higher cortical function but still connetions working from sensory to motor cortex
• 4= withdraws to pain- suggests there is still a physiological reflex response to stimuli
• 3= flexor response to pain- suggests a lesion above the level of the red nuclei (this response is semi-physiological)
• 2= extensor response to pain- suggests a lesion below the red nuclei (this response is not physiological at all)
• 1= no response to pain- suggests severe damage to brainstem +/- cortex

Question 18

Verbal response is one of the components assessed in the GCS score; for each score that can be given suggest what it indicates

Answer 18

Verbal response scored from 5-1:

• 5= orientated in time/place- suggest normal cortical function
• 4= confused conversation- suggests diminished higher cortical function but language centres are still functioning adequetely
• 3= inappropriate words- suggests language centres have been damaged
• 2= incomprehensible sounds- sugests cortical damage with brainstem mediated groans
• 1= no reponse suggests severe dmage to brainstem +/- cortex

Question 19

What does an electroencephalogram do?

Answer 19

Measures combined activity of thousands of neurones in a particular region of cortex

Question 20

Do electroencephalograms have good:

• Temporal resolution
• Spatial resolution

Answer 20

temporal= excellent

spatial= poor

Question 21

Describe the difference between temporal and spatial resolution

Answer 21

In a nutshell, spatial resolution refers to the capacity a technique has to tell you exactly which area of the brain is active, while temporal resolution describes its ability to tell you exactly when the activation happened.

Question 22

What is neuronal synchrony?

Answer 22

Idea that neurones in brain have tendancy to fire synchronously

*NOTE: it occurs commonly in the brain both during physiological and pathological processes such as sleep and epilepsy

Question 23

How can we detect neuronal syncrhony?

Answer 23

EEG (electoencephalogram)

Question 24

State 5 possible functions of sleep (I say possible as we don’t really know the functions)

Answer 24

• Generally unknown
• Energy conservation/repair
• Memory consolidation
• Clearance of extracellular debris
• ‘Resetting’ of CNS

Question 25

State the stages of sleep

Answer 25

* Stage 1 * Stage 2/3 (we often group together as similar) * Stage 4 * REM sleep *Hence, there are 4 major stages and REM*

Question 26

Typically how many cycles of sleep do you pass through in a night?

Answer 26

6 cycles of sleep per night

Question 27

How are the stages of sleep (1,2/3,4 and REM) characterised?

Answer 27

Stages are characterised by their typical EEG pattern

Question 28

Describe how you passes through the stages of sleep

Answer 28

Progress from an awake stage, then to stage 1 etc.... all way down to stage 4 sleep then you move rapidly back up to REM sleep

Question 29

As you go down through the 4 stages of sleep describe what happens to the EEG trace (2 things)

Answer 29

As the neuronal population in cortex become synchronous: * Decreasing frequency * Increasing amplitude

Question 30

Describe the EEG pattern when you are awake with your eyes open, include: * Name of waves * Patttern * Frequency * Amplitude

Answer 30

* Beta waves * Irregular * 50Hz * Low amplitude

Question 31

Describe the EEG pattern when you are awake with your eyes closed, include: * Name of waves * Patttern * Frequency * Amplitude

Answer 31

* Alpha waves * Regular * 10Hz * Low amplitude

Question 32

Describe the EEG pattern when you are in sleep stage 1, include: * Names of waves * Patttern of waves * Frequency * Amplitude

Answer 32

* Background of alpha with interspersed theta waves *(theta waves are regular with frequency of 5Hz)* * Looks similar to when you're awake with eyes closed but has these interspersed theta waves * Alpha waves= 10Hz, theta waves=5Hz * Low amplitude

Question 33

Describe the EEG pattern when you are in sleep stage2/3, include: * Name of waves in this stage * Patttern/what it looks like * Frequency * Amplitude

Answer 33

* Background of thea with interspersed sleep spindles and K-complexes * Sleep spindles= high frequency bursts arising from the thalamus * K complexes= are the emergence of the intrinsic rate of the cortex * Frequency of theta= regular, but sleep spindles & K complexes interfere with this * Sleep spindles and K complexes have higher amplitudes

Question 34

Describe the EEG pattern when you are in sleep stage 4, include: * Name of waves * Patttern * Frequency * Amplitude

Answer 34

* Delta waves *(related to K-complexes seen in stage 2/3- can think of it as they are now all k complexes)* * Regular * 1Hz * High amplitude

Question 35

Describe the EEG pattern when you are in REM sleep, include: * Patttern * Frequency * Amplitude

Answer 35

* EEG similar to beta waves (seen when you are awake with your eyes open) * Reminder that beta waves are:* * *Irregular* * *50Hz* * *Low amplitude* Dreaming occurs in REM stage hence EEG is similar to that of a conscious person

Question 36

In what stage does dreaming occur?

Answer 36

REM sleep

Question 37

Describe the neuronal mechanisms of non-REM sleep

Answer 37

* Complex * But it is the idea that by removing sensory inputs there are fewer positive influences on the positive feedback loop that exists between the reticular formation and cortex (as less somataosensory inputs to reticular formation) * Less positive influences means that there is deactivation of the reticular activating system and hence deactivation of the cortex * This leads to inhibition of thalamus

Question 38

Describe the neuronal mechanisms of REM sleep, include: * Where neurones which initiate REM sleep are found * Why someone in REM sleep is difficul to rouse * Effect of REM on muscle tone * Effect of REM on eye movemetns & CN functions * Effect of REM on autonomics

Answer 38

* Neurones in ponsn initiate REM sleep * Difficult to rouse due to strong thalamic inhibition * Decreased muscle tone due to glycinergic inhibition of LMN * Eye movements & other cranial nerve functions can be preserved e.g. teeth grinding * Autonomic effects are seen e.g. penile erection, loss of thermoregulation

Question 39

Is REM essential for life?

Answer 39

Yes, long term deprivation leads to death

Question 40

State 3 disorders of sleep

Answer 40

* Insomnia * Narcolepsy * Sleep apnoea

Question 41

Describe insomnia, include: * What it is * What it is often caused by

Answer 41

* Difficutly falling asleep or staying alseep or both * Commonly caused by underlying psychiatric disorder as opposed to primary insomnia

Question 42

Describe narcolepsy, include: * What it is * Cause * Is it common

Answer 42

* Person suddenly falls alseep at inappropriate times (decreased ability to regulate sleep-wake cycles) * Some cases caused by mutations in orexin gene; orexin is a peptide transmitter involved in sleep * RARE (but life long. Managed by lifestyle and there are some medications but not always effective)

Question 43

Describe sleep apnoea, include: * What it is * Cause * Symptoms * Whether it is common

Answer 43

* Breathing is interuppted/stops and starts whilst you're asleep * Often caused by excess neck fat leading to compression of airways during sleep causing frequent wakening * Causes excessive daytime sleepiness * Common

Question 44

What is meant by brain death? What will it look like on an EEG?

Answer 44

* Widespread irreversible cortical and brainstem damage * Flat EEG

Question 45

What is a coma? What will the EEG look like?

Answer 45

* State of prolonged unconsciousness where patient is unarousable and unresponsive to psychologically meaningful stimuli due to widespread brainstem and cortical damage * Various disordered EEG pattents with no sleep-wake cycle detectable

Question 46

What is a persistent vegetative state? Describe the EEG

Answer 46

* State of prolonged unconsciousness with some spontaenous eye opening and sometimes localisation to stimuli via brainstem reflexes. * Disordered EEG. Sleep wake cycle dectable.Similar to coma but with some differences (as mentioned)

Question 47

What is locked in syndrome? What is it caused by?

Answer 47

* Patient is aware (conscious) but has complete paralysis of all muscles controlling voluntary movements except eye movements hence they can't communicate *(all somatic motor functions from pons down are lost)* * Occlusion in basilar or pontine arteries

Question 48

Compare and contrast a coma with a persistent vegetative state

Answer 48

Both have: * Disordered EEGs * Widespread cortical & brainstem damage _Coma_ * Unarousable and unresponsive to pyschologically meaningful stimuli * No sleep-wake cycle _PVS_ * Can localise to stimuli via brainstem reflexes * Some spontaneous eye opening * Sleep-wake cycles detected

Question 49

Summarise the EEG traces for all stages of sleep

Answer 49