Reticular Formation + Consciousness Flashcards
What does Arousal mean
State of being oriented towards a goal or avoiding a noxious stimuli
What does consciousness mean
Awareness of internal or external environment
What is Reticular Formation
Population of specialised interneurones in brainstem involved in consciousness
What are the functions of Reticular Formation
Sleep Cardiorespiratory control Autonomic control Motor control Consciousness
What are the sources of input of reticular formation
Cortex
All sensory systems: special, visceral, somatosensory, nociceptive
What are the sites of output of reticular formation
Hypothalamus
Thalamus
Basal forebrain nuclei
Spinal cord
What is reticular activating system
Part of the reticular formation devoted to arousal
What does the RAS consist of
Ascending stimulatory neurones to cortex:
Cholinergic to hypothalamus, histaminergic to cortex
Cholinergic to basal forebrain nuclei, cholinergic to cortex
Cholinergic to Thalamus, glutamatergic to cortex
How does RAS cause arousal
Ascending stimulatory neurones stimulate cortex
Set up positive feedback bw cortex and RF
Arousal occurs in all or nothing phenomenon
Either awake or asleep
What type of neuronal activity occurs in sleep
Why is this
Synchronous neuronal Activity
Neurones fire synchronously when deprived of sensory input
What does electroencephalogram measure
Combined electrical activity of neurones in given part of cortex
What is the trend in EEG patterns during sleep
As you go down stages of sleep, increased amplitude and decreased frequency of EEG traces
Neurones go into synchrony
What does the EEG show with each stage of sleep
Awake/R.E.M - Beta waves (50Hz)
Eyes closed - Alpha waves (10Hz)
Stage 1 - Theta waves (5Hz) in background of alpha waves
Stage 2/3 - K complexes in background of theta waves
Stage 4 - Gamma waves (1Hz) (intrinsic rate of cortex when all sensory input removed)
What is the mechanism of sleep
Inhibition of RAS by inhibitory GABAergic neurones
Loss of cortical stimulation
Loss of positive feedback
Assisted by removal of sensory inputs (e.g. close eyes)
What is R.E.M. sleep
Rapid eye movement sleep
What happens in R.E.M. sleep
High cortical activity - dreams
Muscle paralysis - strong inhibition of thalamus
Eye movements and cranial nerve spared - bruxism
Autonomic effects - direction, loss of thermoregulation
What are the functions of sleep
Bodily repair
Memory: short term to long term consolidation
Clear extracellular debris (Alzheimers and amyloid)
What are the types disorders of sleep
Insomnia
Narcolepsy
Sleep apnoea
What is insomnia
Difficulty sleeping/unsatisfactory sleep which may lead to daytime symptoms
Most often due to mental health issues/anxiety
What is narcolepsy
Neurological condition; impaired regulation of sleep-wake cycle
Patient experiences extreme daytime tiredness, Sleep attacks, cataplexy (Muscle paralysis in response to strong emotion)
What is sleep apnoea
Intermittent and repeated upper respiratory tract muscle relaxation during sleep
This causes arousal or lighter stages of sleep
Patient experiences unsatisfactory sleep and daytime tiredness
What are disorders of consciousness
Brain death
Coma
Persistent vegetative state
What is brain death
Widespread cortical and brainstem damage
Flat EEG
What is coma
Widespread cortical and brainstem damage
Various EEG patterns
Not arousable to psychologically meaningful stimuli
No sleep wake cycle
