10. Reticular Formation Flashcards
What is arousal?
Emotional state associated with some kind of goal or avoidance of something noxious.
What is consciousness?
Hard to define but to do with awareness of external world and internal states.
What two structures are needed for consciousness?
Cerebral cortex and reticular formation.
What is the reticular formation?
A population of specialised interneurones in the brainstem.
What are the inputs to the reticular formation that regulate arousal?
Sensory system, cortex.
What are the outputs from the reticular formation?
Thalamus, hypothalamus, basal forebrain nuclei, spinal cord.
Which part of the reticular formation is devoted to arousal?
Reticular activating system.
What is the feedback loop involved in arousal?
Positive - reticular activating system has stimulatory effect on cortex which stimulates RAS and so on.
Explain the effect the RAS has on the thalamus and thereafter.
ACh neurone acts on thalamus, then glutamate neurone acts on cortex.
Explain the effect the RAS has on the hypothalamus and thereafter.
ACh neurone acts on hypothalamus and histamine neurone acts on cerebral.
Why can antihistamines cause drowsiness?
They block the outflow from hypothalamus acting to stimulate the cortex.
Explain the effect the RAS has on the basal forebrain nuclei.
ACh neurone acts on basal forebrain nuclei and ACh neurones stimulate cortex.
Why can antimuscarinics cause drowsiness?
They block the outflow from the basal forebrain nuclei acting to stimulate the cortex.
How can consciousness be assessed?
Using the Glasgow Coma Scale (GCS) or electroencephalogram (EEG).
What are the things assessed in the GCS?
Eye opening, motor response, and verbal response.
What does an EEG measure?
Combined activity of thousands of neurones in a given part of the cortex to a very high temporal resolution.
What is the baseline firing of neurones in the brain?
Synchronous if undisturbed.
What is the EEG in wakefulness?
B waves, irregular due to interruption from sensory input, frequency 50Hz
What is the EEG with eyes closed?
a wave, regular as deprived of some sensory input, frequency 10Hz.
What is the EEG in stage 1 sleep?
Background of a waves with some theta waves, frequency 5Hz.
What is the EEG in stage 2/3 sleep?
Background of theta waves with sleep spindles (thalamus tries waking cortex, high frequency) and K complex (cortex tends to intrinsic rate with all inputs removed, high amplitude).
What is the EEG in stage 4 sleep?
Delta waves as all inputs removed, frequency 1Hz.
What is the EEG in REM sleep?
B waves like wakefulness as cortex has input from dreams, frequency 50Hz.
How is muscle tone lost in REM sleep?
Descending inhibition of LMNs by glycinergic fibres from reticular formation and running down from reticulospinal tracts.
