0903 - RAS and Attention Flashcards
State how RAS affects motor control
Stimulates spinal pattern generators via descending motor pathways.
Explain how sleep is induced and what a ‘normal’ pattern is
Normal pattern is Stages I-4 (takes 1 hour), then after 1 hour at stage IV, goes back up to 2, then REM (synchronises with increased heart rate, respiration rate and variability, and penile erection). REM gets longer and other stages get shorter as the night progresses. You cannot jump between stages without going through the sequences, and generally wake from REM sleep. Highly ordered process.
Name the stages and sequences in sleep including REM and non-REM sleep phases
5 Stages
Stage 1 - 4-8 Hz (Theta)
Stage II - 10-12Hz (alpha) with spindles of 50-150 microvolts
Stages III/IV - Slow wave (delta) - some quite large - very synchronised brain activity.
REM - low voltage, high frequency beta waves, similar to awake.
Outline why in sleep muscles are relaxed and sensation reduced
Muscle deactivation via glycine release onto motor neurons from reticulo-spinal projections.
Thalamus pre-occupied with itself, prevents anything reaching cortex.
Somatosensory reduction - dorsal column nuclei inhibited via GABA from pontine RAS.
Outline REM sleep.
In REM sleep, when the eyes are moving, the rest of the body muscles are quiet, though increased parasympathetic activity (erection). Cholinergic system is activated.
REM sleep is characterised by dreaming (as opposed to sleep walking/talking), so body is prevented from moving. You are re-running activities through the day, so don’t want active muscles to flail around.
What is the ‘nutshell’ characterisation of REM and non-REM sleep?
Non-REM - inactive brain in an active body.
REM - active brain in an inactive body.
What are the sleep promoting areas of the brain(stem)?
Dorsal reticular formation
Solitary tract nucleus
Ventrolateral preoptic nucleus (VPLO) - KEY
Basal forebrain.
What are the activating systems of the brain(stem)?
Medial reticular formation Locus coeruleus (NA) Raphe nucleus (5-HT) Tuberomammillary nucleus (His) - KEY Forebrain.
What is the central neurotransmitter responsible for arousal? Where is it released from?
Histamine (hence why antihistamine makes you drowsy) - released from the tubero-mammillary nucleus (TMN), projecting to cortex and thalamus.
How does the body induce sleep?
Stimulation of ventrolateral preoptic nucleus (VLPO) leads to gaba-ergic release onto tuberomammillary nucleus (TMN). This shuts of histamine release from the TMN, leading the animal to fall asleep.
How does the thalamus change between sleep and arousal?
Awakeness has the thalamus firing almost constantly. In sleep, there is highly synchronised, but not constant, ‘burst’ firing due to T-type Ca++ channels, leading to ‘sleep spindles’ on the EEG. This exists under positive feedback. Completely pre-occupies the thalamus, and prevents any signals from reaching the cortex.
Illustrate how the system switches between sleep and arousal
“Flip-Flop” mechanism. Under wakeful conditions, the orexin-ergic neurons fire from hypothalamus, stimulating raphe and locus coeruleus nuclei and shifting the body to an awake state. If orxinergic is inhibited, the inputs fall off those nuclei, and ventrolateral preoptic nucleus (VPLO) takes over, inhibiting large parts of the brain.
