Sleep Flashcards
Electroencephalogram
A method of measuring electrical activity in the brain
Rapid eye movement (REM) sleep
Occurs in intervals during the night and is characterised by rapid eye movements, more dreaming and bodily movement and faster pulse and breathing.
Non-REM sleep
A period of sleep characterised by decreased metabolic activity, slowed breathing and heart rate, and absence of dreaming.
Circadian Rhythm
The ‘body clock’ - a cycle that tells our bodies when to sleep, rise, and eat regualting many physiological processes.
Zeitgeber
A rhythmically occuring natural phenomenon that acts as a cue in the regulation of the body’s circadian rhythms.
Suprachiasmatic nucleus
A pair of small nuclei in the hypothalamus of the brain, above the optic chiasm, thought to be concerned with the regulation of physiological circadian rhythms
How is a EEG carried out?
- Non-invasive electrodes placed on standard positions on the head connected to amplifiers and a recording device.
- The letters where the electrodes are placed are named after the lobes. The C denotes the midline of the head.
- On the right hand side, they are evenly numbered and on the left hand side, they are oddly numbered.
- There is a conductive passed used to connect the electrodes to the scalp.
- The signals can be directed through the skull and scalp but also through the meninges themselves.
What are EEGs used for?
Used to help diagnose certain neurological disorders such as seizures in epilepsy
What does the EEG measure?
The combined activity of a large number of similarly orientated neurons.
Reflects summed post-synaptic activity of large cell ensembles
How is a signal detected in an EEG?
Requires synchronous activity across groups of cells for any signal to be detected.
What does the amplitude of an EEG signal depend on?
Depends on how synchronous the activity of the neuron is.
Describe the difference between a synchronous image and an irregular image
If the activity is synchronised, then there is a summed response which can be seen on the EEGs
If the activity is irregular, then the patterns are all different so no sum on the EEG.
What do EEG rhythms correlate to and how are they categoriesed?
Correlate to states of behaviour and categorised by their frequency range.
What does a high-frequency low-amplitude relate to?
Associated with alertness and waking also dreaming
Beta and alpha rhythms
What does a low-frequency high-amplitude relate to?
Associated with non-dreaming sleep or coma
Theta and delta waves
What leads synchronous rhythms?
A central clock or pacemaker e.g. thalamus
How do synchronous rhythms occur?
Arise from the collective behaviour of cortical neurons themselves
How does the thalamus act as a pacemaker?
- Vast input to the cerebral cortex
- Synaptic connections between various excitatory and inhibitory thalamic neurons forcing each individual neuron to conform to the rhythm of the group
- Co-ordinated rhythms are then passed to the cortex by the thalamocortical axons
- A relatively small group of centralised thalamic cells can compel a much larger group of cortical cells
If the rhtyhms of teh cerebral cortex do not rely on the thalamic pacemaker, what do they rely on?
They rely instead on collective interactions of cortical neurons themselves.
Excitatory and inhibitory interconnections of neurons result in a co-ordinated synchronous pattern of activity.
This can remain localised or spread to encompass larger regions of the cortex.
What are the functions of brain rhythms?
The most plausible hypothesis is that most brain rhythms have no direct function, instead they are by-products of things happening in the brain. Rhythms may be an unavoidable consequence of brain circiuts. Although, they do provide an important window to look at the functional states of the brain.
Define sleep
A readily reversible state of reduced responsiveness to, and interaction with, the environment.
Why do we need sleep?
Prolonged sleep deprivation can be devastating to proper functioning. However, we can starve off sleep, but not forever.
What are the three functional states of the brain?
- Wakefulness
- Non-rem sleep
- REM sleep
EEG during wakefulness
High frequency, low amplitude waves
Describe the stage of non-REM sleep
Idling brain in a moveable body.
The body is capable of involuntary movement, and is rarely accompanied by vivid, detailed dreams
Describe the REM sleep stage
An active, hallucinating brain in a paralysed body.
Body is immobilised, accompanied by vivd, detailed dreams. It is more similar to wakefulness on an EEG.
What are the brain rhythms in wakefulness?
Alpha, beta and gamma rhythms
Brain rhythms in REM
Beta and gamma rhythms
4 different stages of brain rhythms in non-REM sleep
Stage 1 - theta rhythms
Stage 2 - spindle (high bursts of activity) and k complex (responding to stimuli)
Stage 3 and 4 - delta rhythms but higher in amplitude in stage 4.
Body functionality in Non-REM sleep compared to wakefulness
- Decreased temperature
- Large decrease in heart rate
- Large decrease in breathing
- Decreased brain energy consumption
Body functionality in REM sleep compared to wakefulness
- Extremely large decrease in temperature
- Decrease in heart rate and irregular
- Decrease in breathing and irregular
- Extremely large increase in brain energy consumption
Describe the sleep cycle
- Each night begins with a period of non-REM sleep
- Sleep stages are then cycled throughout the night, repeating approximately every 90 minutes
- As the night progresses, there is a shift from non-REM to REM sleep.
What are the two theories of why we sleep?
- Restoration
- Adaptation
What is the restoration theory of sleep?
Sleep is important for the restoration of our cognitive processes.
What is the adaption theory of sleep?
Used to conserve energy and hide from predators
Neural mechanisms of wakefulness
- Increase in brainstem activity
- Several sets of neurons that increase their rate of firing in anticipation of wakening and enhance the wake state (e.g. ach, serotonin, NE and histamine)
- These neurons collectively synapse directly with the brain regions involved including the thalamus and the cerebral cortex.
- Increase of input into the thalamus which acts as our pacemaker, there will be an increase in excitatory activity suppressing the rhythmic forms of firing in the thalamus and cortex during sleep.
Neural mechanisms of sleep
- Decrease in brainstem activity
- Decrease in the rate of firing of several neuron.
- Rhythmic firing to the thalamus, causing the block of flow to sensory information up to the cortex.
- Decreased excitatory activity inducing sleep
How do the cholinergic neurons change their activity during REM sleep?
Cholinergic neurons in the pons are shown to increase rate of firing to induce REM sleep. This is a theory to why we dream. This may activate regions of the brain associated with memories and emotion but the semi-random firing translates it into non-sensical and vivid dreams.
What are 4 other sleep promoting factors?
- Adenosine
- Nitric Oxide
- Inflammatory factors
- Melatonin
Adenosine and sleep
If adenosine receptors are activated, there is decreased heart rate, respiratory rate and smooth muscle tone (decreasing blood pressure). Adenosine receptor antagonists promote wakefulness (caffeine).
Nitric oxide and sleep
Potent vasodilator causing decreases smooth muscle tone, decreasing blood pressure also stimulating the release of adenosine.
Inflammtory factors and sleep
Cytokines stimulate the immune system to fight infection. Interleukin-1 levels are shown to promote non-REM sleep linking to the adaptation theory to protecting ourselves and recooperating. Sleepiness is a familar consequence of infection.
Melatonin and sleep
A hormone secreted by the pineal body at night. Shown to initiate and maintain sleep - role in natural sleep-wake cycle remains unclear.
What happens during the daily rhythms of the body?
Most physiological processes rise and fall with the daily rhythms
What happens when the daylight-darkness cycles are removed from an animals environment?
The circadian rhythms continue due to the body having a “brain clock”.
What are zeitgebers?
Environmental time cues
How can a human be separated by zeitgebers?
Location studies in deep caves as it is free from all environmental cues.
What is the state humans are in if there is no zeitgebers?
“Free-running” state - internal biological clock of approximately 24.5 - 25.5 hours
What is the body’s biological clock?
The suprachiasmatic nucleus (SCN)
What is the suprachiasmatic nucleus?
A small nucleus of the hypothalamus directly above the optic chiasm that receives retinal innervation and synchronises circadian rhythms with the daily light-dark cycle.
What happens when the SCN is abolished or inhibited?
Animals will still have co-ordinated sleep with the light-dark cycles present. The rhythm was disrupted but they still slept.
What are the retinal cells that synchronise the SCN?
Specialised photoreceptor cells expressing the photopigment melanopsin - not rods or cones.
Describe the SCN mechanism
- Photoreceptors expressing melanopsin are slowly excited by light and can detect changes in luminosity.
- This is projected back to the SCN, inhibiting the production of melatonin by the pineal gland disrupting the onset of sleep when it is light.
