L11 - Brain Rhythms: EEG, Sleep & Diurnal Rhythms Flashcards
What is an electroencephalogram?
A measurement of the collective electrical activity of the neurones in a particular region of the brain
Why is EEG only effective for detecting cortical activity?
Because electrodes must be placed on the surface of the patient, so only surface electrical activity can be measured effectively
What might be seen on an EEG in a patient with epilepsy?
When might this phenomenon be seen in individuals without epilepsy?
- In patients with epilepsy, there is sudden abnormal synchronisation across all inputs from the electrodes
- Synchronisation occurs outside of epilepsy in:
1 - Cognition, particularly pattern recognition
2 - Sleep
Define sleep.
What are the stages of sleep?
- A readily reversible state of reduced consciousness
1 - REM sleep
2 - Stages 1-4 of non-REM sleep
What changes with the stages of non-REM sleep?
There is increased synchrony with later stages of non-REM sleep (greater synchrony towards stage 4)
What are the characteristics of REM sleep?
1 - Rapid darting eyes
2 - Easily aroused by meaningful stimuli
3 - When awakened, appear alert and attentive
4 - Dreaming
5 - Loss of muscle tone
Describe the normal pattern of sleep stage progression during sleep.
1 - Initially, sleep begins at REM then oscillates down and up the stages of REM and non-REM sleep
2 - Sleep stages become less deep as sleep progresses (e.g. only reaching stage 2 at maximum rather than stage 4)
3 - Periods of brief awakening start to occur between cycles
4 - REM sleep increases in duration
5 - Sleep ends
Which network of nerves is thought to form part of the neural basis of wakefulness?
Where is this structure located?
- The reticular activating system
- It is located in the brainstem
How does the reticular activating system contribute to wakefulness?
- Sensory information in ascending tracts and motor information in descending tracts to / from the brain pass through fibres of the reticular activating system to the thalamus
- The neurones of the reticular activating system use ACh and aminergic neurotransmitters at the thalamus to allow this information to be passed to the cortex via this order sensory neurones
Why does REM sleep appear similar to wakefulness on an electroencephalogram?
Because, similar to wakefulness, the neurones of the reticular activating system carrying sensory information also use ACh (but not aminergic neurotransmitters) during REM sleep, allowing some sensory information to pass to the cortex
*This is why REM is also more similar to wakefulness than sleep beyond electroencephalograms
Why can antihistamines cause drowsiness?
Because histamine is one of the aminergic neurotransmitters used by the reticular activating system during wakefulness
List 2 physiological changes in the brain that occur with non-REM sleep.
1 - Decreased ACh & aminergic pathways
2 - Increased ventrolateral preoptic nucleus (VLPO) activity
Accumulation of which neurotransmitter determines waking time?
Adenosine
What is the suprachiasmatic nucleus?
A nucleus involved in the control of circadian rhythms
How can the circadian rhythm be reset?
- The circadian rhythm can be reset with light via direct retinal input to the suprachiasmatic nucleus
- This retinal input is known as a zeitgeber
