The Brainstem, Arousal & Sleep Flashcards
Where is the reticular formation?
At the centre of the brain stem
Functions of the reticular formation?
Sleep regulation Motor control Cardioresp control Autonomic functions Motivation and reward Controls the level of sensitivity the upper brain receives
What is the reticular formation made up of?
Discrete nuclei embedded in the white matter
What are the two classifications of the reticular system?
Ascending reticular activating system (ARAS) - increases levels of consciousness
Secondary inhibition centre - decreases activity of the brain, reducing the level of consciousness
How does the ARAS act and what inhibits the ascending reticular activating system to allow sleep?
Filters incoming signals
Hypothalamic sleep centres
What is the ascending reticular activating system formed by?
Projection of the reticular formation
How does LSD work?
Acts on the ARAS to reduce the filtering of incoming signals to higher centres of the brain
Alcohol can also inhibit this region
What inputs does the ARAS have?
Auditory Nociceptive Visual Somatosensory Visceral Olfactory
Where does the ARAS output to?
The motor system (fibres descend in the cord to alter sensitivity of motor nuclei in the ventral horn)
Autonomic centres
Thalamus
Cortex
All raise level of consciousness
During consciousness and REM sleep, what is the ARAS doing?
Stimulating thalamo-cortical neurones
-stimulates cortex for consciousness
Stimulating inhibitory neurones to act on inhibitory inter-neurones, further stimulating the consciousness of the cortex
During slow wave sleep, what is the ARAS doing?
Neurones from the ARAS are silent, meaning no thalamo-cortical neurones are firing and there is significantly reduced consciousness
What type of neurotransmitter is between the ARAS and thalamus?
Acetylcholine
What happens when either the ARAS of cerebral cortex don’t work and cannot communicate?
Locked-in syndrome - brainstem damage
Persistent vegetative state - damage to cortex
Brain death - no activity on EEGs
What is a coma?
A state of unconsciousness from which the person cannot be aroused using pain, light or sound
Patient initiates no voluntary movement
Causes of a coma?
Intoxication Metabolic disturbances -diabetes -hypoxia Neurological events -stroke -tumour -trauma
What are some pathological alterations in the level of neurotransmitters in the brain and what can they cause?
Too much dopamine - schizophrenia
Low serotonin - depression
Low ACh from destruction of secreting cells - Alzheimer’s
What are EEGs?
Measure electrical activity (excitatory and inhibitory) of the neurones by placing 16-25 electrodes on the scalp
What are the different waves seen in an EEG?
Alpha (high frequency) - seen when awake and eyes shut. There is constant feedback between the cortical and thalamic projections
Beta - seen when awake with eyes open (mainly from parietal and frontal lobes)
Theta - seen in children and strong emotion in adults (parietal and temporal lobes)
Delta (low frequency) - deep sleep and serious brain conditions
What is sleep important for?
CNS resetting/clearance
Memory (converts short-term to long-term)
Homeostasis
What controls sleep?
The reticular formation and hypothalamus
What is active and inactive during non-REM sleep?
Body is active
Brain is inactive
What physiological changes happen in non-REM sleep?
Decreased cerebral blood flow Decreased oxygen consumption Decreased body temperature Decreased BP Decreased resp rate Decreased BMR
What is active/inactive during REM sleep?
Active brain
Inactive body
What is seen on an EEG during REM sleep?
Appears as if awake - same projections happening between reticular formation, thalamus and cortex
