NEUR533 - Brain rhythms and sleep Flashcards
LEARNING OUTCOMES
What is measured with an electroencephalogram (EEG)
- cerebral cortex general activity
- Diagnose sleep disorders/epilepsy/research
What does MEG stand for?
Magnetoencephalography (MEG)
Concerning EEG rhythms, what are beta HERTZ and behavioural states?
15 - 30 Hz - activated or attentive cortex
Concerning EEG rhythms, what are alpha HERTZ and behavioural states?
8 - 13Hz
- Quiet waking state
Concerning EEG rhythms, what are Theta HERTZ and behavioural states?
4 - 7 Hz
- Some sleep and waking states
Concerning EEG rhythms, what are Delta HERTZ and behavioural states?
Less than 4Hz
Deep sleep
High synchrony
High EEG amplitute
What’s the part of the brain to be associated with neuronal oscillations, and massive cortical input as a PACEMAKER?
THALAMUS - Nucelus reticularis thalami (NRT)
Regulated also by voltage-gated ion channels
- Hyperpolarization =
Review EEG on thalamus and cortical interaction
3 function brain sleeps
EEG RYTHMS DURING SLEEP STATES
- Hippocampus has a replay memory sorting and consolidation
- All memory is stored within the hippocampus via LTP
FOCUS ON THE DIFFUSE MODULATORY NEUROTRANSMITTER SYSTEMS - LEARN THEM PROPERLY
MORUZZI’S RESEARCH
learn key components of the waking/sleeping modulatory systems
- Not getting visual stimulation in sleep
- Having visual input from higher regions in the brain
- Visual information is not being accurately interpreted by the frontal cortex regions in sleep
REM ON - Cholinergics
REM OFF - Serotonergics
SLEEP PROMOTING FACTORS
Gene expression during sleeping and waking
- Has light sensitive ganglionic neurons in SCN
- Right above optic chiasm
- SCN (within the hypothalamus)
- Orchestrator of the circaidian rhythm
Clock genes
REtinal ganglion cells and SCN
What is the name of the clock genes regulated by the SCN?
Cryptochrome
WHICH BRAIN MECHANISMS MODULATE SLEEP?
- SCN of the hypothalamus
- Brain’s biological ‘clock genes’
- Light via retino-hypothalamic tracts
- Melatonin
- Orexins - neuropeptides produced in dorsal hypothalamus (control of appetite and arousal working as NT)
High frequency, low amplitude rhythms are associated with what?
Alertness and waking or the dreaming stages of sleep
Low-frequency, high-amplitude rhythms are associated with what?
Non-dreaming sleep states
Drugged states
Comas
If cortical neurons have high synchronicity - would this increase EEG amplitude? Y/N
Yes
What are the 2 thoughts about the generation of synchronous rhythms in EEG?
(1) They may all take their cues from a central clock, or pacemaker
or (2) they may share or distribute the timing function among themselves by mutually exciting or inhibiting one another.
What’s the difference between a partial and generalized seizure?
Generalised seizure: involves the entire cerebralcortex of both hemispheres
Partial seizure: involves a particular area of the cortex
In both cases, the neurons within the affected areas fire with a synchrony that never occurs during normal behavior. As a consequence, seizures are usually accompanied by very large EEG patterns.
Absence seizures characterize a childhood form of epilepsy, consisting of less than 30 seconds of generalized, 3 Hz EEG waves accompanied by loss of consciousness.
Definition of sleep?
Sleep is a readily reversible state of reduced responsiveness to, and interaction with, the environment
What are key elements of phase 2 sleep?
- last 5–15 minutes.
- 8–14 Hz oscillation (ALPHA)
- sleep spindle,- generated by a thalamic pacemaker
-High-amplitude sharp wave (K complex)
What are key elements of phase 3 sleep?
- EEG begins large-amplitude, slow delta rhythms.
- Eye and body movements are few.
What are key elements of phase 4 sleep?
- deepest stage of sleep,
- large /slow EEG rhythms of 2 Hz or less
- During the first cycle of sleep, stage 4 may persist for 20–40 minutes.
Then sleep begins to lighten again, ascends through stage 3 to stage 2 for 10–15 minutes, and suddenly enters a brief period of REM sleep, with its fast EEG beta and gamma rhythms and sharp, frequent eye movements.
When does the predominant amount of REM sleep occur throughout the night?
Last third
How long can the longest REM period last?
30 - 50 minutes
Usually followed by a period of at least 30-minutes of NON-REM SLEEP before the next REM occurs
What are the most critical neuronal systems to control sleeping and waking?
Diffuse modulatory neurotransmitter systems
What NT does the brain stem modulatory neurons use to fire during waking and enahce critical REM events?
- Norepenephrine
- Serotonin
- Acetylcholine
The diffuse modulatory systems control the rhythmic behaviours of the ….?
Thalamus
which in turn controls many EEG rhythms of the cerebral cortex; slow, sleep-related rhythms of the thalamus apparently block the flow of sensory information up to the cortex.
Sleep also involves activity in _______________ of the diffuse modulatory systems, such as the inhibition of motor neurons during dreaming.
- Decending branches
Several sets of neurons increase their firing rates in anticipation of awakening and during various forms of arousal. They include neurons of the diffuse modulatory systems…
- 3.
- 5.
- Locus coeruleus = norepinephrine
- Raphe nuclei = serotonin
- Basal forebrain = acetylcholine
- Midbrain = histamine
- Hypothalamus = hypocretin (orexin)
Collectively, these neurons synapse directly on the entire thalamus, cerebral cortex, and many other brain regions.
= depolarization of neurons,
= neuronal excitability,
= suppressed rhythmic firing.
Where is orexin (hypocretin) secreted from
Laeral hypothalamus
What does orexin do?
Strongly excite:
cholingeric,
noradrenergic,
sertonergic,
dopaminergic and
histaminergic modulatory systems
PROMOTES WAKEFULNESS
INHIBITS REM
What sleep disorder does a loss of hypocretin (orexin) lead to?
Narcolepsy
Early stages of non-REM sleep include the EEG _________, des- cribed earlier, which are generated in part by the inherent rhythmicity of thalamic neurons
Sleep spindles
As non-REM sleep progresses, spindles disappear and are replaced by ________________ (less than 4 Hz)
slow delta rhythms
Synchronization of activity during spindle or delta rhythms is due to neu- ral interconnections within the thalamus and between the _________ and _________.
Thalamus
Cortex
What is narcolepsy?
Excessive daytime sleepiness can be severe and often leads to unwanted “sleep attacks.”
What is hypocretin?
Orexin
What does hypocretin do?
Strongly excite:
cholingeric,
noradrenergic,
sertonergic,
dopaminergic and
histaminergic modulatory systems
PROMOTES WAKEFULNESS
INHIBITS REM
What are zeitgebers?
Environmental time cues (light/dark, temperature and humidity vari- ations)
The light-sensitive ganglion cells express a unique type of photopigment called _________, which is not present in rods and cones. These neurons are very slowly excited by light, and their axons send a signal directly to the __________ that can reset the circadian clock that resides there.
melanopsin
SCN
What is thought to regulate the suprachiasmatic nucleus to stay on a 24-hr clock cycle without light/dark innervation?
clock genes
known as period (per), cryp- tochrome, and clock.
How is the SCN clock genes thought to work?
a negative feedback loop
A clock gene = transcribe mRNA
mRNA = proteins
Increased Proteins send feedback loop
= decreased protein synthesis
= 24hrs
▲ FIGURE 19.28
Control pathways from the SCN to peripheral circadian clocks. The SCN regulates circadian clocks throughout the body (including the liver shown here) via its control over the ANS; core body temperature; cortisol and other hormones; and feeding, locomotion, and metabolism. (Source: Adapted from Mohawk et al., 2012, Fig. 3.)
