Sleep Mechanisms, Cognition and Memory Flashcards
What is the intrinsic property of the cortex?
Without other influences the activity of the cortex reverts to slow waves and activity becomes synchronised i.e. remove cortex from ascending inputs leads to S-wave sleep
What part of the brain controls Arousal?
A major part of the brain which controls arousal is the ascending reticular activating system (ARAS) - part of the reticular formation in the midbrain
From where does the ARAS receive input?
All of the major sensory systems and makes connections with the hole of the brain and the spinal cord. Stimulation of the ARAS = arousal from sleep
What effect do norepinephrine/noradrenaline and epinephrine/adrenaline have on the ARAS?
The circulating levels in the bloodstream increase arousal
Describe the level of activity of the sensory inputs in the neurons of the ARAS when the subject is in the waking state
The sensory input levels remain high
What do changes in state of consciousness require in relation to the ARAS?
Changes to occur in the ARAS also. Therefore for sleep to happen, the ARAS has to be inhibited
For slepp to happen, what must happen to the ARAS?
It must be inhibited
What is responsible for the cycles of S -> D D -> S sleep that occur through the night?
Oscillatory action in two areas of the reticular formation.
What two areas in the reticular formation are responsible for the S->D cycles in the night? What type of action causes the cycles?
Gigantocellularis Tegmental Field (GTF)
Local Coerulus
Oscillatory action
Describe the GTF
The field consists of very large cells with incredibly long axons and dendrites that make multiple connections throughout the brain. A single GTF cell may contact a million other cells throughout the brain
Describe the action of the GTF
It exhibits oscillatory activity, burst of APs appearing just before and during REM sleep. The GTF is the origin of the PGO spikes which give the visual component of dreams.
The GTF action modifies cortical activity directly and through the ARAS. As the GTF stimulates the ARAS, and the ARAS causes wakefulness, this is part of the reason that the sleep changes from synchronised to desynchronised, and this combined with the GTFs direction stimulation of the cortex to produce the S to D part of the sleep cycle
What type of neurons make up the GTF?
Cholinergic neurons
Give a side effect of cholinesterase inhibitors in relation to the sleep cycle
Because the neurons of the GTF are cholinergic, cholinesterase inhibitors increase the action of acetylcholine by preventing its breakdown, therby stimulating the GTF which then further stimulates the ARAS and the cortex directly. This means that S to D increases and so a side-effect of cholinesterase inhibitors is to increase REM sleep i.e. likely increase nightmares/dreams
What is the action of the locus coeruleus?
It releases norepinephrine, acting as an oscillator with the GTF. When the LC cells are active, the GTF cells are not, and this removes the stimulatory action of te GTF on the cortex and the ARAS, providing the D to S part of the sleep cycle. i.e. the LC and GTF both oscillate but produce opposing responses, together forming the alternating D to S and S to D cycles of sleep
Describe the circadian rhythm of biological systems
Biological systems show oscillations within roughly a 24hour period
What has overall control of the circadian rhythm?
The ‘master-clock’ in the suprachiasmatic nucleus (SCN) of the hypothalamus, just above the optic chiasm
What is the suprachiasmatic nucleus (SCN)?
The biological ‘master-clock’ that controls the body’s circadian rhythm. Its neurons exhibit inherent 24 hour cycles
What effect does the hypothalamus (SCN specifically) have on the orexin neurons? What effect does this have? What use does orexin have as a treatment?
Inhibition from the hypothalamus turns the orexin neurons off at night. As orexin stimulates wakefulness, it is important for the inhibition to occur at night in order to allow for sleep. Orexin is a possible treatment for insomnia
What are some of the influences that develop the 24 hour cycles learned by the neurons of the SCN?
Light/dark cycles - some optic nerve fibres pass to the SCN
Temperature
What happens to the circadian sleep cycle if the SCN is destroyed?
Although the specific connections between the SCN and the have not been fully identified, the sleep cycle is destroyed if the SCN is lost
What happens to the circadian sleep cycle if people have cues as to light or time?
They gradually increase their day length to 25-30hours
What are the health effects of working shifts over a 10 year period?
The incidence of CVS and GI disease increases three-fold
What I cognition?
It relates to the highest order of brain function and relates to the behaviour that deals with thought processing
What is the fuction of the limbi system with regard to cognitive function and our emotions?
It acts as the link between our higher cognitive function and the ‘more basic’ emotional responses
