10. SLEEP Flashcards
What are brain rhythms?
- Brain rhythms are distinct patterns of neuronal activity that are associated with arousal, sleep state & specific behaviours
How can brain rhythms be measured?
- Brain rhythms can be measured with EEGs
What is an EEG?
- Electroencephalogram measures electrical activity produced by the brain
- EEG involves placing non-invasive electrodes onto the scalp
What produces EEG signals?
The combined activity of large groups of similarly orientated neurones produces EEG signals
- Requires synchronous activity to produce summed action potential EEG signals
What are the two main categories of brain waves?
- HIGH AMPLITUDE, LOW FREQUENCY = Wakefulness & Alertness
2. LOW AMPLITUDE, HIGH FREQUENCY = Non-dreaming sleep
What are the four types of brain waves?
- Beta
- Alpha
- Theta
- Delta
What are the characteristics of beta waves?
- Beta waves have a high frequency & low amplitude
- 14 -30 Hz
- Awake with mental activity
What are the characteristics of alpha waves?
- Alpha waves have a high frequency & low amplitude
- 8 -13 Hz
- Awake & resting
What are the characteristics of theta waves?
- Low frequency, high amplitude
- 4- 7 Hz
- Sleeping
What are the characteristics of delta waves?
- Low frequency, low amplitude
- < 4Hz
- Deep sleep
What are the two ways to generate synchronous brain rhythms?
- Synchronous brain rhythms can be generated with:
1. PACEMAKER
2. COLLECTIVE BEHAVIOUR
What is the pacemaker of the brain?
- Thalamus
How does the thalamus generate synchronous activity?
- A small group of central thalamic neurones can influence a large group of cortical neurones
- The thalamic neurones project into the cerebral cortex
- Synaptic connection between the excitatory & inhibitory thalamic neurones, forces each individual neurone to follow the rhythm
- These co-ordinated rhythms will then be passed on to the cortex
Describe the collective behaviour of cortical neurones to produce synchronous brain rhythms?
- In some regions of the cerebral cortex, the rhythms rely on collective interactions of the cortical neurones
- Co-ordinated patterns of synchronous activity are produced due to the interconnections between cortical neurones
Define sleep
- Sleep is a reversible state of reduced responsiveness or decreased interaction with the environment
What are the characteristics of the brain rhythm for wakefulness?
- High frequency, low amplitude
Describe sensation, thought & movement for wakelfulness?
- SENSATION = vivid, externally generated
- THOUGHT - Logical progressive
- MOVEMEMENT - Continuous, voluntary
What are the two types of sleep?
- NON-REM SLEEP
2. REM SLEEP
What is non-REM sleep?
- In NON-REM sleep, the body is capable of involuntary movement. Sleeping is rarely accompanied by vivid dreams
What is the brain rhythm for NON-REM sleep?
- Low frequency, high amplitude
What happens to thought, sensation & movement during NON-REM sleep?
- SENSATION - Dull/absent
- THOUGHT - Logical, repetitive
- MOVEMENT - occasional, involuntary
What is REM sleep?
- REM sleep is a state of muscle paralysis (immobilised) accompanied by vivid dreams
What is the brain rhythm for REM sleep?
- REM sleep has high frequency, low amplitude brain waves
What happens to thought, sensation & movement during REM sleep?
- SENSATION = vivid, internally generated
- THOUGHT = bizarre, illogical
- MOVEMENT - muscle paralysis
What happens to temperature in non-REM & REM sleep?
- Core body temperature drops for both REM & NON-REM sleep
- But temperature drops more in REM sleep
What happens to heart rate & breathing in non-REM & REM sleep?
- Heart rate & breathing rate both decrease in REM & NON-REM sleep
- But heart rate & breathing rate is much lower for NON-REM sleep
- Heart rate & breathing are irregular during REM sleep
What happens to brain oxygen/energy consumption during REM/NON-REM sleep?
- During NON-REM sleep - brain energy consumption decreases
- But during REM sleep, brain energy consumption increases, which is balanced by the drop in muscle movement (paralysis)
Describe the characteristics of a sleep cycle?
- Sleep begins with non-REM sleep &gradually progresses into REM sleep.
There are four stages of sleep, where it cycles between REM sleep and non-REM sleep - ## The sleep stages are then cycled, repeating every 90 minutes
What are the two proposed theories for the function of sleep?
- RESTORATION - restore & recover to prepare for next day
2. ADAPTATION - Sleep is a way to conserve energy & protect us
What happens to brain stem activity during wakefulness?
- During wakefulness, there’s increased brain stem activity
- Increased firing of brain stem neurones, to produce neurotransmitters that promote wakefulness
- These neurones project to the thalamus & cortex
- Effect of brain stem neurone is inhibitory, supressing thalamus & cortex
What happens to brain stem activity during sleep?
- During sleep, there’s decreased brain stem activity
- Decreased firing from the brain stem, reduces the inhibitory output on thalamus & cortex
- Thalamus is no longer suppressed
- Both thalamus & cortex are active
- But the rhythmic firing of the thalamus blocks the flow of sensory information into the cerebral cortex during sleep
Which area of the brain is associated with dreaming and is active during sleep?
- The pons is active during sleep & is thought to be associated with dreaming
- There’s increased firing if cholinergic neurone sin the pons, which is associated with dreaming
- Activates areas of cerebral cortex which are involved in eliciting emotions & memories
What are 4 sleep promoting factors?
- ADENOSINE
- NITRIC OXIDE
- INFLAMMATORY MEDIATORS
- MELATONIN
What is adenosine?
- Adenosine the building block for ATP
- It accumulates throughout the day
How does adenosine promote sleep?
- Adenosine binds to it’s receptor to cause decreased heart rate, respiratory rate & decreased contraction of smooth muscle. Overall, reducing blood pressure
- Adenosine also has an inhibitory effect on neurotransmitters that promote wakefulness such as acetylcholine, serotonin etc.
- Adenosine is highest in the late evening to induce sleep & begins to fall during sleep
What can adenosine antagonists do?
- Adenosine antagonists can bind to the adenosine receptor to promote wakefulness as it prevents the induction of sleep
- Caffeine is a adenosine antagonist
What is nitric oxide?
- Nitric oxide is a potent vasodilator, which dilate blood vessels causing a drop in blood pressure
How can nitric oxide promote sleep?
- Nitric oxide decreases blood pressure
- Nitric oxide also stimulates adenosine release
- Adenosine stimulates sleep, by blocking the neurones that produce neurotransmitters involved in wakefulness
How can inflammatory mediators promote sleep?
- Inflammatory mediators can be released during infection
- Interleukin 1 can promote sleepiness
Where is melatonin released from?
- Melatonin is a hormone released by the pineal gland
How does melatonin promote sleep?
- Melatonin levels rise in the late evening & peak in the early hours of the morning (e.g 1AM).
- Melatonin levels fall just before we wake
- Melatonin is involved in initiating & maintaining sleep
What is a circadian rhythm?
- A circadian rhythm refers to any period of rhythm within 24 hours
- E.g sleep/wake
What are zeitgebers?
- Zeitgebers are environmental time cues such as temperature, light, humidity
What is the suprachiasmatic nucleus?
- SCN is a small nucleus in the hypothalamus which receives input from retinal innervation
- The SCN synchronises the circadian rhythm with the daily light/dark cycle
What happens in the absence of the SCN or cues?
- In the absence of cues, the SCN is still able to regulate circadian rhythms
- If the SCN is inhibited, sleep can still be coordinated with light/dark cycles
How does the SCN regulate the rhythmicity of circadian rhythms?
- SCN clock genes produce a protein
- This protein feeds back to the SCN to inhibit production of the protein by decreasing gene expression
- Negative feedback of protein
- Light information form retina resets SCN neurones
- Each individual SCN neurone is a biological clock
- SCN has control over circadian clocks in our body e.g stomach, liver
