Brain rhythms and sleep Flashcards
Why does brain electrical activity vary?
Changes in accordance to what the person is doing. It has a structure-function relationship. e.g. more activity in occipital lobe when using vision
What is a disordered rhythm?
A change in pattern or activity when it is not expected
What is an ECG?
An electroencephalogram to record electrical activity in different states. 1 electrode measures an area of the brain.
What is a cortical pyramidal neuron?
The large neurons that produce large excitatory signals in the cortex that can be detected.
How do neurones produce a big signal?
Work collectively through synchronous activity.
What causes the synchronous firing of neurons and why is it important?
Pacemaker. Neurons are active all the time without a need for input. The thalamic neurons have an intrinsic rhythm which drives the cortex to be active when sensory input is recieved.
Synchronousy can be normal or abnormal depending on the situation.
In normal conditions how does synchronous firing occur for cognition?
In very fast GAMMA oscillations e.g. when first presented with an image there is an increase in oscillation to determine if it is recognisable.
What electrical activity fires when awake and thinking and listening?
Asynchronous BETA oscillations at 13-30Hz
What electrical activity fires when awake but relaxed?
Asynchronous ALPHA oscillations at 8-13Hz
What electrical activity fires when asleep?
Synchronous slow high waves of THETA and DELTA.
What is the definition of sleep and how is sleep characterised?
A readily reversible state of reduced consciousness. A decrease in mobility and decrease in responsiveness to sensory inputs, due to reduced cortical excitability. Sleep is not the absence of wakefulness.
What type of behaviour is sleep?
Motivated - Not a reflex. It can be modified according to context e.g. can override need for sleep
What influences how sleep is achieved?
Experience and learning - External cues can trigger sleep e.g. getting into bed
What is the evolutionary function of sleep?
To recuperate and conserve energy
What happens in people who are sleep deprived / have reduced quality and quantity of sleep?
Impairs cognitive performance
Decreases mood
Alters physical health both metabolic and immune
What are the stages of sleep?
Awake
REM
Stage 1 - 4 (deep sleep)
What is REM and how is it characterised?
Rapid eye movement sleep characterised by desynchronised BETA activity, rapid darting eyes, loss of muscle tone and easily aroused by a meaningful stimulus to an an alert and attentive state.
In which stage of sleep does dreaming occur mainly?
REM but can occur in the other stages
What influences the drive of sleep?
The thalamus. Its influence increases throughout the stages of sleep.
What type of firing occurs in non-REM sleep?
Stage 1 - Theta
Stage 2 - Theta, spindle and K complexes
Stage 3 - Delta
Stage 4 - Delta
How do the stages change throughout sleep?
The stage of REM increased throughout the night and deep sleep decreases.
Which stage of sleep is entered on first entry into sleep?
Stage 1, don’t enter REM straight away.
What controls arousal?
Reticular Activating System - keeps individual awake while active.
What is the RAS?
Multiple areas of neurons that stimulate the cortex through ACh and aminergic activity
Which nuclei of RAS use ACh?
LDT and PPT
Which nuclei of RAS use monoamines?
TMN, Raphe and LC
What monoamines are used in RAS?
Histamine, 5-HT and NA
Why can antihistamines cause drousiness?
Block histamine needed for arousal in RAS
Which nuclei control the drive for sleep and how?
VLPO - suppresses amine neurones through the release of GABA and Galanin.
Which nuclei are active in REM sleep?
Ach activity remains the same so PPT and LDT remain active, but amine activity is altered inducing paralysis (Raphe, LC, TMN)
What is the flip-flop theory?
Sleep and wake activity balance is either one or the other, it can’t be both at once.
What affects waking time?
Adenosine accumulation - At high levels it causes a switch from wake to sleep
What substance can affect the waking time?
Caffeine as it is a adenosine receptor antagonist and therefor prevents sleep
How does physical activity affect sleep?
Induces a person to sleep earlier but not for longer
What is the circadian rhythm?
The natural internal system that regulates feeling of tiredness and wakefulness over 24hr period.
What controls the circadian rhythm?
Suprachiasmatic nucleus in response to light. SCN is in the hypothalamus and receives direct retinal input, that doesn’t pass to the visual cortex. The rhythm is controlled via the altered protein synthesis and degradation of the protein Kaic in response to light.
How does retinal input affect tiredness?
It provides an awareness of how much light in passing through the retina to determine if it is day or night time. Affects the synthesis of Kaic.
What is sleep apnoea?
Interuption to normal respiration when asleep, with sudden arousal as O2 levels fall.
What is insomnia?
Unusual disruptive sleep. Can be short term or long term. The pattern of disturbed sleep varies depending on what is normal for the pt.
What can cause insomnia?
Hunger 5-HT depletion Withdrawal from hypnotics e.g. caffeine PD Increased age AD (sleep during day due to reduced ACh) Schizophrenia Depression
How does depression affect sleep?
Depression levels rise with sleep. Experience more REM and may enter REM more rapidly, without entering stage 4 sleep when first falling asleep.
There is a correlation but causation is unknown: Depression cause insomnia or insomnia cause depression.
Who is mostly affected by deep sleep disorders?
Children - overcome as the brain matures
Causes bed wetting, sleep walking and night terrors
What is REM sleep/behavioural disorder?
Mostly affects females over 50. There is a loss of muscle tone causing them to act out dreams during REM e.g. talking, limb twitching, jerking
What increased risk is behavioural disorder linked to?
Precursor to PD
What is narcolepsy?
Uncontrollable entry into sleep or cataplexy (sudden muscular weakness triggered by strong emotions)
What causes narcolepsy?
Destruction of lateral hypothalamus that causes a defect in the neurons that produce orexin/hypocretin for stabilising wakefulness.
How does hypocretin affect wakefulness?
Connected to sleep/wake ACh and amine neurons
What does the deficiency in orexin cause?
A defective flip-flop
What is an advantage of sleep?
Promotes learning and memory
How is the theory that sleep helps learning and memory used in therapy?
Sleep deprivation will reduce traumatic memories as less sleep = less memory.
Sleeping soon after a non-traumatic exposure to a phobia stimulus will help with memory processing of the non-threatening situation.
Depression may be reduced by staying awake.
