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Sem 4: Nervous System > 8b.) Consciousness > Flashcards

8b.) Consciousness Flashcards

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1
Q

What is consciousness?

A
  • Hard to define
  • Related to awareness of external environment and internal states
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2
Q

What is arousal?

A

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

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3
Q

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

A

Cerebral cortex

Reticular formation

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4
Q

Where do conscious thoughts arise?

A

Cerebral cortex

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5
Q

What is the role of the reticular formation

A

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

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6
Q

Where does reticular formation receive inputs from?

A

Cerebral cortex and sensory systems

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7
Q

What fibres connect the cortex and reticular formation?

A

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

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8
Q

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

A

Positive feedback loop

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9
Q

When are positive feedback loops seen?

A

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

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10
Q

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
A

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)
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11
Q

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

A

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

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12
Q

Summarise the outputs from the reticular formation

A
  • 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
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13
Q

What is the reticular formation?

A

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.

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14
Q

Clinically, what is used to assess consciousness?

A

GCS score

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15
Q

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

A
  • Eye opening (scored 1-4)
  • Motor response (scored 1-6)
  • Verbal response (scored 1-5)
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16
Q

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

A

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
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17
Q

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

A

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
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18
Q

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

A

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
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19
Q

What does an electroencephalogram do?

A

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

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20
Q

Do electroencephalograms have good:

  • Temporal resolution
  • Spatial resolution
A

temporal= excellent

spatial= poor

21
Q

Describe the difference between temporal and spatial resolution

A

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.

22
Q

What is neuronal synchrony?

A

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

23
Q

How can we detect neuronal syncrhony?

A

EEG (electoencephalogram)

24
Q

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

A
  • Generally unknown
  • Energy conservation/repair
  • Memory consolidation
  • Clearance of extracellular debris
  • ‘Resetting’ of CNS
25
Q

State the stages of sleep

A
  • Stage 1
  • Stage 2/3 (we often group together as similar)
  • Stage 4
  • REM sleep

Hence, there are 4 major stages and REM

26
Q

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

A

6 cycles of sleep per night

27
Q

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

A

Stages are characterised by their typical EEG pattern

28
Q

Describe how you passes through the stages of sleep

A

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

29
Q

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

A

As the neuronal population in cortex become synchronous:

  • Decreasing frequency
  • Increasing amplitude
30
Q

Describe the EEG pattern when you are awake with your eyes open, include:

  • Name of waves
  • Patttern
  • Frequency
  • Amplitude
A
  • Beta waves
  • Irregular
  • 50Hz
  • Low amplitude
31
Q

Describe the EEG pattern when you are awake with your eyes closed, include:

  • Name of waves
  • Patttern
  • Frequency
  • Amplitude
A
  • Alpha waves
  • Regular
  • 10Hz
  • Low amplitude
32
Q

Describe the EEG pattern when you are in sleep stage 1, include:

  • Names of waves
  • Patttern of waves
  • Frequency
  • Amplitude
A
  • 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
33
Q

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
A
  • 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
34
Q

Describe the EEG pattern when you are in sleep stage 4, include:

  • Name of waves
  • Patttern
  • Frequency
  • Amplitude
A
  • 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
35
Q

Describe the EEG pattern when you are in REM sleep, include:

  • Patttern
  • Frequency
  • Amplitude
A
  • 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

36
Q

In what stage does dreaming occur?

A

REM sleep

37
Q

Describe the neuronal mechanisms of non-REM sleep

A
  • 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
38
Q

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
A
  • 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
39
Q

Is REM essential for life?

A

Yes, long term deprivation leads to death

40
Q

State 3 disorders of sleep

A
  • Insomnia
  • Narcolepsy
  • Sleep apnoea
41
Q

Describe insomnia, include:

  • What it is
  • What it is often caused by
A
  • Difficutly falling asleep or staying alseep or both
  • Commonly caused by underlying psychiatric disorder as opposed to primary insomnia
42
Q

Describe narcolepsy, include:

  • What it is
  • Cause
  • Is it common
A
  • 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)
43
Q

Describe sleep apnoea, include:

  • What it is
  • Cause
  • Symptoms
  • Whether it is common
A
  • 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
44
Q

What is meant by brain death?

What will it look like on an EEG?

A
  • Widespread irreversible cortical and brainstem damage
  • Flat EEG
45
Q

What is a coma?

What will the EEG look like?

A
  • 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
46
Q

What is a persistent vegetative state?

Describe the EEG

A
  • 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)
47
Q

What is locked in syndrome?

What is it caused by?

A
  • 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
48
Q

Compare and contrast a coma with a persistent vegetative state

A

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
49
Q

Summarise the EEG traces for all stages of sleep

A

Sem 4: Nervous System (21 decks)

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