8.2 Reticular formation: Control of consciousness Flashcards
Define arousal
The emotional state associated with some kind of goal or avoidance of something noxious
Define consciousness
Something to do with ‘awareness’ of both external world and internal states
What are the 2 aspects required for consciousness?
Cerebral cortex and reticular formation
What is formed from the association of these 2 elements?
A positive feedback loop of excitation
What do positive feedback loops usually control in the body?
Binary decisions
What is the reticular formation?
A population of specialised interneurons in the brainstem
What are the inputs of reticular formation?
Somatosensory system
Cerebral cortex
What are the 3 major output sites from reticular fibres?
Basal forebrain nuclei
Hypothalamus
Thalamus
What neurotransmitter is released from each of the reticular output sites?
Basal forebrain nucleus- Ach
Hypothalamus- Histamine
Thalamus- Glutamate
Through that do the reticular fibres project out?
Reticular activating system (RAS)
What is the RAS devoted to?
Arousal
What is used to assess consciousness?
GCS
What are the categories within GCS?
Eye opening
Best motor response
Best verbal response
How does each mark correspond to function?
4- Full cortical function
3- Transient disruption to CNS
2- Cortex not working so rely on brainstem reflex
1- Completely unrousable
What is used to assess consciousness?
EEG (electroencephalogram)
What are the stages of sleep?
Stage 1- light sleep 2 3 4- deepest stage REM- rapid eye movement sleep
Describe EEG show in an awake state?
50 Hz
Beta wave form
Irregular rhythm
Describe EEG show in an stage 1 state?
Alpha waves
10 Hz
Increasing synchronisation
Describe EEG show in stage 2 and 3?
Background alpha waves
But sleep spindles -from thalamus jerk opening
And K complex
Describe EEG show in stage 4
Delta waves
High altitiude
Slow waves
Describe EEG show in REM sleep
Same as awake waves= morphology is the same
Beta waves
Describe the neural mechanism of sleep
Deactivating the reticular activating system (and hence cortex) and inhibiting the thalamus- slowing down the positive excitatory loop
Assisted by the removal of sensory inuts
What is REM sleep also known as?
Paradoxical sleep
How is REM sleep is initiated?
By groups of neurones in the pons?
Why is REM sleep person difficult to arouse despite beat waves like awake state?
Strong inhibition of the thalamus
How does REM sleep prevent movement and acting out of dreams?
Muscle tone in most of the tofu is lost due to descending inhibition of LMN’s by glyvubergic fibres arising from reticular formation and running down the reticulospinal tracts
Whichn significant functions are preserves and which are not?
Eye movements and autonomic effects e.g. penile erection are preserved
Loss of thermoregulation
What are the functions of sleep?
Enigmatic
Energy conservation and bodily repair
Memory consolidation
Clearance of extracellular debris- alzheimer’s
What are some sleep disorders?
Insomnia- secondary to other problem e.g. depression and anxiety
Narcolepsy
Sleep Apnoea
What are some disorders of consciousness?
Brain death
Coma
Persistent vegetative state?
Locked in syndrome?
