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.
