S8) The Brainstem, Arousal, Sleep and Consciousness Flashcards

1
Q

What is arousal?

A

Arousal is the emotional state associated with some kind of goal or avoidance of something noxious

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2
Q

What is consciousness?

A

Consciousness has something to do with ‘awareness’ of both external world and internal states (difficult to define, but measurable)

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3
Q

Two basic ingredients are required for consciousness.

What are they?

A

Consciousness = cerebral cortex + reticular formation

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4
Q

What is the reticular formation?

A

The reticular formation is a population of specialised interneurones in the brainstem

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5
Q

Numerous inputs regulate the level of arousal.

Where do they come from?

A
  • Sensory system
  • Cortex
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6
Q

The reticular formation has widespread outputs.

Where do these go to?

A
  • Thalamus (sensory gating) (GLUT)
  • Hypothalamus (Histamine)
  • Basal forebrain nuclei (Ach)
  • Spinal cord (muscle tone)
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7
Q

Which assessment might one use to assess consciousness?

A

Glasgow Coma Scale

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8
Q

Which investigation might one use to assess consciousness?

A

The electroencephalogram (EEG) measures the combined activity of thousands of neurones in a given part of the cortex to a very high temporal resolution

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9
Q

How many different stages are there in sleep? Explain

A

5 stages – during the night you typically pass through around 6 cycles of sleep, progressing from an awake state down through to stage 4 and then periodically going from stage 4 rapidly up into REM sleep

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10
Q

Provide a brief interpretation of the sleep on an EEG

A

Going down through the 4 stages, the EEG shows decreasing frequency and increasing amplitude as neuronal populations in the cortex become synchronous due to reduction of sensory input

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11
Q

Describe the following tracings of the different stages of sleep in this EEG:

A
  • Awake – low voltage, random, fast (beta waves)
  • Drowsy – alpha waves; more regular
  • Stage I – theta waves; more regular and synchronised
  • Stage II/III – sleep spindles and K complexes
  • Stage IV – delta waves
  • REM sleep (beta waves)
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12
Q

Describe the neural mechanism of sleep

A

Deactivating the reticular activating system and inhibiting the thalamus:

  • The positive feedback loop between RAS and cortex is inhibited, leading to decreased cortical activity
  • Inhibition of the positive feedback loop is assisted by removal of sensory inputs

(stimulating cortex stimulates the RF which the stimulates the cortex + feedback)

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13
Q

What initiates REM sleep?

A

REM sleep is initiated by groups of neurones in the pons

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14
Q

In four steps, describe the paradox of REM sleep

A

EEG similar to that seen during arousal (beta waves), but hard to rouse due to strong inhibition of the thalamus

Majority of muscle tone is lost due to descending inhibition of LMNs by glycinergic fibres arising from the reticular formation (paralysed)

Preservation of eye movements and some other cranial nerve functions (teeth grinding)

Autonomic effects are seen e.g. penile erection, loss of thermoregulation

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15
Q

What are the functions of sleep?

A

Enigmatic:

  • Energy conservation and bodily repair
  • Memory consolidation
  • Clearance of extracellular debris
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16
Q

Identify three sleep disorders

A
  • Insomnia (mental health, bladder issues)
  • Narcolepsy (RARE)
  • Sleep apnoea (people with fat neck can’t breathe)
17
Q

What is insomnia?

A

Insomnia is a sleep disorder where people have trouble sleeping and is often due to psychiatric/psychological causes

18
Q

What is narcolepsy?

A
  • Narcolepsy is a long-term neurological disorder that involves a decreased ability to regulate sleep-wake cycles
  • It is characterised by excessive sleepiness, sleep paralysis, hallucinations
19
Q

What is sleep apnoea?

A

Sleep apnoea is a serious sleep disorder that occurs when a person’s breathing is interrupted during sleep due to fat around neck

20
Q

Identify four disorders of consciousness

A
  • Brain death
  • Coma
  • Persistent vegetative state
  • Locked in syndrome
21
Q

What is brain death?

A

Brain death is widespread cortical and brainstem damage (flat EEG)

22
Q

What is a coma?

A
  • A coma is a disorder of consciousness due to widespread brainstem and cortical damage, with various (disordered) EEG patterns detectable
  • The patient is unarousable and unresponsive to psychologically meaningful stimuli
  • No sleep-wake cycle detectable
23
Q

What is locked in syndrome?

A
  • Locked-in syndrome is a condition that can be caused by basilar/pontine artery occlusion
  • Eye movements can be preserved, but all other somatic motor functions lost from the pons down
24
Q

What is PVS?

A
  • PVS is a disorder of conscious due to widespread cortical damage, with various (disordered) EEG patterns detectable
  • Similar to coma but with some spontaneous eye opening, can also localise to stimuli via brainstem reflexes
  • Sleep-wake cycle detectable
25
Q

what are the Hertz of the different waves involved in the sleep cycle

A

awake: 50hz

eyes closed: 10 Hz

stage 1: 5Hz

stage ⅔/4 : 1Hz

26
Q

reticular formation diagram

A