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