2.5 Consciousness Flashcards by Will Bradley

NREM sleep makes up __% of sleep

75%

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Which arm of the autonomic nervous system is more active during NREM/REM sleep?

NREM: Parasympathetic
REM: Sympathetic

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REM sleep makes up __% of sleep

25%

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What happens to sensation during REM/NREM sleep?

NREM: Limited/absent
REM: Vivid, internally generated

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Describe muscle activity during REM sleep

Movements are commanded, but none are carried out

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Why is REM sleep called paradoxical sleep?

EEG looks more awake than asleep.

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Oxygen consumption of brain during REM vs NREM

REM: Elevated
NREM: Decreased

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How are muscles paralyzed during REM sleep?

Glutamatergic neurons in the brainstem activates neurons in the medulla. They release GABA, inhibiting the activity of skeletal muscles.

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Describe the four stages of NREM sleep

Stage 1: Hypnagogic hallucinations

Stage 2: Harder to awaken

Stage 3: Few eye and body movements

Stage 4: Sleep talking

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Describe the sleep cycles

Move from stage 1 to stage 4 of NREM. Back up to stage 1 sequentially, and into REM. This is one sleep cycle.

With each cycle, we spend less time in N3 and N4, and longer in REM.

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Describe the two mechanisms by which neurons can create synchronous rhythms

Central pacemaker (orchestra conductor)
Inhibiting/exciting one another (all playing)

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Gamma EEG waves

Conscious perception/problem solving

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Beta EEG waves

Waking state; alertness

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Alpha/Mu EEG waves

Quiet waking state. Relaxed, lucid, calm.

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Theta EEG waves

Deep relaxation/light sleep; meditation

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Delta EEG waves

Deep sleep

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What EEG waves can be found in someone who is awake/in REM sleep?

Beta waves (gamma can also be found in wakefulness)

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What EEG waves can be found in someone who is in Stage 3/Stage 4 NREM sleep?

Delta waves

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What EEG waves can be found when we are drowsy/relaxed?

Alpha waves

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What EEG waves are most prominent in Stage 1 NREM sleep?

Theta waves

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What happens to EEG activity between Stage 1 and Stage 2 sleep?

More theta
Increased amplitude
Sleep spindles (inhibit cognitive processes)
K complexes (memory consolidation)

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This part of the reticular formation is responsible for promoting wakefulness…

Ascending reticular activating system (ARAS)

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How is the ARAS activated?

By the release of a peptide called orexin from the lateral hypothalamus

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In order to fall asleep, we need to inhibit ARAS. How is this done, and by what system?

VLPO (Ventrolateral preoptic area) releases GABA to inhibit ARAS modulatory neurons

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How does adenosine progressively make us sleepier?

Takes foot of ARAS accelerator (reduces orexin release). Puts foot on ARAS brake (increases GABA release from VLPO)

How does caffeine make us less sleepy?

Binds to adenosine receptors

Give some examples of zeitgebers

- Sunlight - Food - Exercise - Social interactions

Describe how the suprachiasmatic nucleus regulates sleep/wake cycles in response to sunlight

- Increases Orexin release from LH - Decreases GABA release from VLPO - Decreases melatonin release from pineal

Why is melatonin called the dracula hormone?

- Released in response to dark - Inhibited release in response to light

How is it thought that melatonin makes us sleepy?

- Decreases orexin from LH - Increases GABA from VLPO

Define consciousness

Full awareness of the self and one's relationship to their environment

Define coma

Patient has closed eyes and is unable to interact with their environment (GCS 8 or less)

What are the two main components of consciousness?

- Arousal - Awareness

Which neuroanatomical areas are responsible for arousal?

Thalamic/extrathalamic ascending systems

What is the relationship between awareness and arousal in terms of interdependence?

Awareness requires arousal, but arousal does not require awareness.

Describe the structure of the neuroanatomical regions responsible for awareness

- Distributed neuronal circuits - Modular in nature - Loop from thalamus and cortex

Lesions in which brain areas can lead to coma?

- Cortex - Thalamus - Brainstem

What is brain death? How is it different from death?

- Permanent loss of all brain activity - Occurs when a patient dies whilst on life support; if life support is removed, the patient will die.

What is a minimally conscious state?

- No ability to follow instruction or communicate - Appears to have awareness of surroundings Minimal = only just passing = can do it, but can't follow INSTRUCTIONs (maybe better...)

What is a vegetative state?

Complete unawareness of the self and the environment — but seems to be awake. Awake but not aware (like the microbiome of on a piece of brocolli)

Locked in syndrome

- Alert wakefulness - Inability to move or speak

What is akinetic mutism?

- Very infrequent movement or speech - Well preserved eye movements; can speak or move occasionally if directed

What is the role of the hypothalamus in the baroreceptor response to low BP?

Stimulates vasopressin release -> fluid retention -> increase BP

Define syncope

Sudden, transient loss of consciousness due to cerebral hypoperfusion

List some different causes of syncope by category

- Reflex (e.g. vasovagal) - Cardiac (e.g. structural heart disease, arrhythmia) - Neurologic (e.g. CVA) - Psychogenic (e.g. anxiety) - Other (e.g. anaemia) PRNC= Prank = Face syncope = first cause in acronym

Which type of syncope has the worst prognosis

Cardiac origin (e.g. arrhythmia, structural heart disease)

Vasovagal syncope mechanism

- Higher cortical sites trigger exaggerated sympathetic activity - Followed by increased parasympathetic tone - Bradycardia, dilation of blood vessels - Cerebral hypoperfusion -> syncope

Vasodepressor vs cardioinhibitory vasovagal syncope

Vasodepressor: loss of arterial blood pressure Cardioinhibitory: Bradycardia/asystole (In most vasovagals, both are involved)

Prodromal symptoms of vasovagal syncope

- Sweating - Dizziness - Epigastric discomfort - Nausea

Describe the mech of how increased intrathoracic pressure can cause situational syncope

- Increased ITP - Vena cava compression - Decreased venous return - Decreased intra-aoritc pressure (baroreceptors) - SNS activation - When pressure released: increased PNS activation - Bradycardia - Cerebral perfusion down - Bye bye

Is orthostatic hypotension/syncope associated with increased vagal response?

- No - Rather, an insufficient baroreceptor-mediated sympathetic response to standing

Why are older adults at increased risk of orthostatic syncope?

- Decreased baroreceptor responsiveness - Polypharmacy

What are some reasons why pregnancy can increase likelihood of syncope?

- Progesterone lowers BP - Dehydration (e.g. morning sickness) - Iron deficiency anaemia

Can hypoglycaemia cause syncope?

- Not often — only in old patients on glucose-lowering drugs for diabetes. - It mimics syncope, but does not have to have cerebral hypoperfusion

True or false: hyoglycaemic crisis causes no change (or an increase) of postural tone

True

True or false: syncope in the presence of cardiac cause is more sinister than vasovagal syncope

True. Not good.

Syncope red flags

- Occurs during exercise - Pupils aren't equal in size - Precipitated by severe headache - Double vision - Back/abdo pain (aortic dissection)

Explain how raised ICP can cause a vicious cycle

Raised ICP -> Lowered CPP -> Hypoxia -> Oedema -> raised ICP -> death

Investigations for a comatose patient

- EUC/LFT, glucose, creatinine - ABG, CRX, ECG (if o2 concerns) - Lumbar puncture (exclude meningitis) - Toxicology (?Alcohol/drugs) - CT/MRI

Other than brain masses/lesions/infections, what are some other causes of coma?

- Organ failure - Epilepsy - Psychogenic - Metabolic

Patient has focal neuro dysfunction, progression, localising deficit, and coma. Is the lesion supra or infratentorial?

Supratentorial

Patient has immediate coma, pupil/occulomotor/respiratory abnormality. Is the lesion supra or infratentorial?

Infra

Delirium associated with a coma, and seizures. What is the common cause?

Metabolic

Describe treatment of patient with coma

- ABC (Airway, breathing, circulation) - Get to scanner as fast as possible - If structural: neurosurg registrar. If metabolic: medical registrar. (Basically: keep them alive, work out what's wrong, then find who can fix it)