Session 8 - Lecture 2: Control of Consciousness Flashcards
Define consciousness.
Awareness of the external world and your own internal state. This requires a functioning cerebral cortex and reticular formation.
Define arousal.
Emotional state associated with goal/avoidance of noxious event.
What is the reticular formation and what are its functions?
The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. The reticular formation plays a role in sleep and consciousness, pain modulation, somatic motor control, cardiovascular control and habituation. The RF is a grey matter tissue with inputs from the sensory system and cortex and outputs to the thalamus, hypothalamus, basal forebrain nuclei and spinal cord.
What part of the reticular formation is devoted to arousal?
Reticular activating system (ascending inputs that keep the cerebral cortex active i.e. wakefulness).
How can you assess consciousness?
The Glasgow coma scale and EEG.
Describe an EEG trace during sleep.
Awake - beta waves, irregular, fast, 50Hz.
Eyes closed - alpha waves, more synchronous, 10Hz.
Stage 1 - alpha waves in background (slower) and theta waves, 5Hz.
Stage 2/3 - theta waves in background, buzz of activity = sleep spindle which is a burst of thalamic activity (consolidation of memory), K complex = delta wave, 1Hz = intrinsic rate of cerebral cortex.
Stage 4 = delta waves, 1Hz.
REM sleep = low voltage, random, fast with sawtooth waves (similar to awake).
Describe the neural mechanism of sleep.
Deactivating the reticular system and inhibiting the thalamus. Inhibition of RAS and cortex reduces cortical activity which is assisted by removal of sensory inputs.
What is the REM paradox?
REM sleep is often called paradoxical sleep because EEG graphs of the brainwaves show that the brain is very active, despite the appearance that you’re fast asleep. There are bursts of alpha and beta waves, just as if you’re awake.
Describe the mechanisms involved in REM sleep.
Pons neurones initiate REM sleep, the thalamus is inhibited. Descending LMN fibres reduce muscle tone running down the reticulospinal tract. Eye movement is preserved, may get nocturnal bruxism, autonomic effects are seen i.e. penile erection and loss of thermoregulation. REM sleep is essential for life.
What are functions of sleep?
Energy conservation and bodily repair
Memory consolidation
Clearance of extracellular debris
‘Resetting’ of CNS
Give some example of sleep disorders.
Insomnia - can be due to depression, anxiety and alcohol.
Narcolepsy - fall asleep unexpectedly, perhaps with emotional stimuli.
Sleep apnoea - pauses in breathing, airway collapses, obesity is a risk factor, also low orexin (neuropeptide important in wakefulness and muscle tone in airways).
Give some example of disorders of consciousness.
Brain dead - widespread cortical and brainstem damage, flat EEG.
Coma - same as brain dead but various disordered EEG patterns, unresponsive, no sleep-wake cycle detectable.
Persistent vegetative state - like coma but with some spontaneous eye opening, sleep-wake cycle detectable.
Locked in syndrome - can be caused by basilar/pontine artery occlusion. Eye movements can be preserved but all other somatic motor functions lost from the pons down.
