10.5 Reticular Activating System Flashcards
Where does the reticular formation lie?
From caudal medulla to rostral midbrain
What are the 3 columns of nuclei?
In the median column – the raphe nuclei
In the medial column – magnocellular nuclei (because of larger size of the cells)
In the lateral column – parvocellular nuclei (because of smaller size of the cells)
How much sleep do we need?
8 hours between 10:30 and 6:30 but this increases at birth and decreases with age
What happens to the sleep requirement in juveniles
They need slightly more sleep (9-10) due to their hormonal status and their circadian rhythm is shifted to a later window (1am-10am)
What are the stages of sleep?
Stage I: 4-8Hz (theta)
II: increasing 10-12 Hz (alpha)
III - IV: deep sleep - slow wave
REM: low, voltage high frequency
What is the cycle of sleep?
Descent into sleep takes about 1 hour, once stage IV has been reached the systems starts to revert back into active REM state with first phase shortest, subsequent ones of longer duration
It is an ordered process and you cannot jump between stages of sleep
How many phases do you have and when do you most often wake up?
Tend to have 4-5 REM phases waking up mostly from REM phase
What occurs in REM phase?
Rapid eye movement, but little EMG activity, increased ANS activity (HR, erection)
Dreaming
‘active brain in an inactive body’
When do sleep talking and walking usually occur?
In non REM sleep ‘inactive brain in an active body’
What neuromodulatory system is active in REM sleep and what areas of the brain?
cholinergic system is activated
Limbic system becomes activated but prefrontal cortex and posterior cingulate become less active
What NT is involved with arousal?
Histamine from tuberomamillary body in hypothalamus which will signal via H1-3 receptors
What part of the hypothalamus is important in activating sleep?
Ventrolateral preoptic nucleus
What system in the hypothalamus is active during waekefulness?
Orexinergic system
What happens with VPLO and orexin during sleep?
When the VPLO is activated it will send inhibitory signals to the monoaminergic neurons and orexin neurons (shuts down histaminergic activation)
What causes sleep spindles in an EEG and how does this differ from an awake state?
Thalamic reticular cells inhibit thalamocortical cells causing hyperpolarisation, this activates T-type Ca channels which generates Ca spike which feeds back onto reticular cells
In an awake state the RAS and neuromodulatory input depolarisation followed by regular firing
What are the physiological changes in sleep?
Reduced response to somatic sensory stimuli - inhibition of DC nuclei via GABA from pontine RAS
Muscle relaxation caused by glycine release from interneurons activated by reticulo-spinal projections (except pharynx/larynx muscle and respiratory muscles)
What are the sleep pormoting areas?
Dorsal reticular formation
Solitary tract nucleus
Ventrolateral preoptic nucleus
Basal forebrain
What are the activating areas of the brain?
Medial reticular formation Locus coeruleus Raphe nucleus Tuberomammilary nucleus Forebrain
How do benzodiazepines affect sleep?
Put you into Stage I straight away
Prolonged deep sleep
Shorter REM phases
Create lasting ‘hangover
How does caffeine effect sleep?
Delays ascending into deep sleep with re-awakening
Shortened overall sleep, REM and deep sleep
What is the mechanism of arousal?
Arises as a consequence of activation of all neuromodulatory systems
Switched on by hypothalamic interactions (His) via negative feedback to the VLPN
In REM sleep what part of the brain is active and what isnt?
limbic system active, prefrontal cortex is not
What is the role of histamine in sleep?
Histamine is released from the tuberomamillary nuclei of the hypothalamus which gets input from VPLO and Orexin
When released = awake, decreased in sleep (antihistamines make you drowsy)
Stimulation of which nucleus would lead to sleep in a normal person?
Ventrolateral preoptic nucleus - when stimulated it will send inhibitory signals to the monoaminergic neurons and orexin neurons (shuts down histaminergic activation)
