8. Reticular formation & control of consciousness Flashcards Preview

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Flashcards in 8. Reticular formation & control of consciousness Deck (11):

What is consciousness and which brain structures does it require?

"Awareness" of both external world and internal states.

Requires +ve feedback loop between CEREBRAL CORTEX and RETICULAR FORMATION.


What is arousal?

Emotional state associated with some kind of goal or avoidance of something noxious.


What is the reticular formation? Describe its inputs and outputs.

Reticular formation = population of specialised interneurones in the brainstem involved in consciousness and arousal.

Inputs from:
- sensory system (e.g. can't sleep when light/noisy)
- cortex (e.g. can't sleep when anxious)

Outputs to:
- thalamus (sensory gating)
- hypothalamus
- basal forebrain nuclei
- spinal cord (muscle tone)


What is the reticular activating system?

Part of the reticular formation devoted to arousal, including stimulation of the cortex via the:
- thalamus: glutaminergic neurones to cortex
- hypothalamus: histaminergic neurones to cortex
- basal forebrain nuclei: receive cholinergic input from RF and project cholinergic neurones to cortex


How is level of consciousness assessed?

Glascow Coma Scale (GCS) - assesses:
1. eye opening (spontaneous, response to speech, nil)
2. motor response (obeys, localises, withdraws, abnormal flexor response, extensor response, nil)
3. verbal response (oriented, confused conversation, incomprehensible sound, nil)



Do neurones fire synchronously when asleep or awake?

When asleep


Describe the wave pattern seen on EEG when awake with eyes open and with eyes closed.

Awake with open eyes = beta waves
- high frequency (50 Hz)
- irregular due to complex processing

Awake with eyes closed = alpha waves
- lower frequency (10 Hz)
- more regular due to deprivation of input


Describe the wave pattern seen on EEG during the stages of sleep.

Stage 1
- background alpha waves (10 Hz)
- occasional theta waves (5 Hz)

Stage 2/3
- background of theta waves (5 Hz)
- occasional sleep spindles (short period of increased thalamus activity stimulating cortex)
- occasional K complexes (intrinsic cortical rate)

Stage 4
- delta waves (slow intrinsic cortical rate, high amplitude due to synchronicity of neuronal firing)

REM sleep
- beta waves - dreaming provides visual input to cortex


where are the neurones located for REM sleep located?



Describe the state of arousal seen in REM sleep

- EEG activity similar to that seen during arousal (beta waves)
- person difficult to rouse due to strong inhibition of thalamus
- muscle tone in most of body is lost due to descending inhibition of LMNs by glycinergic fibres arising from the reticular formation and running down the reticulospinal tracts
- eye movements and some other cranial nerve functions are perserved (e.g. nocturnal bruxism)
- autonomic effects are seen inc. penile erection and loss of thermoregulation


describe 3 disorders of consciousness

1. Persistent vegetative state
- widespread cortical damage
- various (disordered) EEG patterns detectable
- unarousable and unresponsive to pyschologically meaningful stimuli but with some spontaneous eye opening (can even localise to stimuli via brainstem reflexes)
- sleep-wake cycle detectable

2. Coma
- widespread brainstem and cortical dysfunction
- various (disordered) EEG patterns detectable
- unarousable and unresponsive to pyschologically meaningful stimuli
- no sleep-wake cycle detectable

3. Brain death
- widespread cortical and brainstem damage
- flat EEG