Sleep, brain rhythms and EEG Flashcards
What two key factors are considered in diagnosing disorder based on electrical activity
- region of electrical activity
2. Behaviour person undertaking e.g. if asleep brain activity has a particular rhythm which may be disordered in disease
Describe how an EEG works
- place electrodes on the skull surface
- electrodes measure collective activity of many surface neurons usually pyramidal neurons
- when the neurons active in the same manner this synchronous activity will leader to a higher intensity on the EEG
What is the major limitation of EEGs
Only surface neurones so cannot give indication of the deeper structures of the brain such as thalamus or brainstem
What two basic factors do we look at on an EEG
The intensity of signal
The rhythm of activity
Which we compare this to other regions of the brain
What normal situations will you see an increase in intensity of an EEG
Increase in intensity of an EEG is due to an increase in synchronous activity
This can occur in:
- In normal cognition
- This is used as basis for optical illusions where when when found solution to illusion never tricked again as got synchronous activity of fast gamma oscillations where neurones working together in different parts of brain
- Hence linked to perception - Sleep:
- When you go through awake state to sleep state synchronisation increases, indicated by larger intensity of signal (large peaks) and even through phases of sleep the synchronisation increases
What are the three classifying factors of sleep
we can classify sleep by what you observe which is decreased mobility (don’t physically move as much), less responsive to sensory input and as a result the cortex is less excited
Define sleep and why is it different to a coma
sleep is a “a readily reversible state of reduced consciousness”
A coma is not reversible because you cannot be aroused when in a coma, you can be woken up from sleep
What are 4 benefits of sleep and how were they discovered
Benefits:
- lack of sleep can impair mood and cognition
- escape predators
- cell repair
- conserve energy
we know it is important to health as all animals do it and if disrupted can lead to decreased health VICE VERSA so too much sleep issue as well.
Also, the extremes of age tend to sleep longer, so got some importance
Describe the different rhythms in awake state and through stages of sleep
Awake: alpha and beta rhythms REM: beta rhythms Stage 1: theta rhythms Stage 2: theta + spindles + K complexes Stage 3: delta rhythms Stage 4: >50% delta rhythms
stages numbered are of non- REM sleep
How can we distinguish REM sleep from the awake state and why is this difficult based on EEG
Distinguish based on:
- rapid eye movements key feature based on where the oculomotor nerve leaves brainstem ( at mid-brain superior colliculus)
- it different to active as the brainstem is largely inhibited so that have decreased muscle tone so don’t act out dreams
Difficult as beta rhythms only in REM sleep which is one of the rhythms seen when active, and shows desynchronised activity indicated by small peaks in EEG similar to when awake.
What stages of sleep do dreams occur
All of them the idea it is just in REM sleep is a myth
What is a hypnogram and state its three key findings
Hypnogram is a graph which tracks stages of sleep you in with time
- as you sleep you progress down each stage of sleep then back up in a cycle
- As you continue sleeping you go back up the stages at a lower stage e.g. first cycle go to stage 4 but second cycle may go up at stage 3 to stage 2. This means the deepest sleep occurs at the start of sleeping
- As you increase time of sleep the time in the REM stage gets progressively longer most likely as getting ready to be aroused
What is arousal and what causes you to be aroused from sleep
Arousal is sensory arousal where wake up from sleep and is due to the reticular activating system
Describe the reticular activating system and how it links to arousal
The reticular activating system represent a group of neurons
These neurons can be split into those using ACH as a neurotransmitter and those using amines as a neurotransmitter i.e. aminergic neurons
the activation of aminergic neurons allow the cortex to receive sensory information from the thalamus and the acetylcholine neurons allow the thalamus to receive sensory information from the brainstem
As long as these neurons are allowing sensory information to be received by the thalamus and transmitted to the cortex you will be aware of sensory stimuli and so awake
What is state of RAS in the REM sleep
REM sleep is similar to the awake state as the ACH neurotransmitters are firing but the aminergic aren’t so you are asleep
In addition, the descending pathways inhbited in the brain stem by RAS so have decreased muscle tone
What drugs can make you sleepy and how has this changed its manufactures
Antihistamines can oppose the activity of aminergic neurones using histamine as neurotransmitter because they are histamine receptor antagonists
to counter this issue use forms of antihistamines which cannot cross BBB and so get into the brain
What changes in the RAS and other parts of brain take you down stages of sleep from REM
In non REM sleep get decreased activity of both ACH and aminergic neurones in RAS
Also get INCREASED activity of the VPLO which are a group of neurones in the hypothalamus which help bring you down through stages of sleep
Is sleep due to the absence of activation of RAS
No as in non REM sleep get INCREASED activity of the VPLO which are a group of neurones in the hypothalamus which help bring you down through stages of sleep
Describe the flip flop theory
It is the idea that as sleep is active process it is a balance of factors than merely the absence of activation of RAS that causes you to be in sleep state rather than wake state
it is like on see-saw and depending on factors can be pushed to one state or another, these factors include adenosine, circadian rhythm and physical activity as well as others
this makes sense as REM sleep is very similar to wake state but shift of certain other factors puts you more to sleep state than wake state
What 3 main factors induce sleep
- waking time which is like clock ticking down from once awake so when awake for too long at certain point will induce sleep this is mediated by adenosine
- physical activity
- circadian rhythm
Why does caffeine keep you awake
It inhibits action of adenosine involved in determining waking time as caffeine is an adenosine receptor antagonist
Describe the formation of circadian rhythm
the suprachiasmatic nucleus (SCN) =
‘body clock’ and drives the natural circadian rhythms by breakdown and synthesis of proteins it is like clock ticking
retinal input can reset this is known as zetigeber (giving of time)
State 4 clinical links to circadian rhythm
- jet lag
- shift workers
- chronotherapeutics when to give drugs if want in night day or mid-day depending on your circadian rhythm e.g. cortisol levels highest in morning
hypnogram in depression and schizophrenia what are key features
no stage 3 and 4 sleep
REM is longer and not gradually increasing as night goe son
Describe deep sleep disorders
More in childre lead to sleep walking, night terrors and bedwetting
should correct self
Describe REM disorder and what disease linked to
Loss of inhibition by brainstem to muscle tone
so act out on dreams
linked to parkinsons
Describe narcolepsy and link to obesity
Suddenly flop from sleep to wake states and loose muscle tone (cataplexy)
orexin(hypocretin) in lateral hypothalamus and promotes RAS activation
orexin linked to feeding so link to obesity
so less orexin less regulation of RAS so just flip flop from awake to sleep rapidly
as less orexin must be that orexin helps with feeling of satiety
Describe basis of use of sleep as a phobia therapy or CBT and depression
sleep promotes learning and memory
so in natural disasters where sleep deprived don’t form traumatic memories as easily
use in therapy as after positive therapy/ CBT sleep so reinforces the knowledge
deprive people of sleep some don’t show depression
Describe some types of sleep disorders and why hard to define insomnia
sleep apnoea insomnia - hunger - 5-HT depletion - withdrawal from hypnotics -illness depression
hard to define insomnia as individual hypnogram varies
