Neuro: Sleep Flashcards
What is an electroencephalogram (EEG)?
A measurement of electrical activity generated by the brain and recorded from the scalp
What exactly is does each electrode of an electroencephalogram (EEG) measure?
Each electrode measures the combined activity of a large number (1000s) of similarly orientated neurons.
Why does the activity of a large group of neurons need to be synchronous in order for an electroencephalogram to detect their activity?
- Because when the activity of a large group of neurons are synchronous their electrical activity is able to be added or summed so that they can produce a strong signal on the EEG
- When the activity isn’t synchronous the electrical activity of those neurons aren’t able to be added so the signal on the EEG isn’t strong
Different electroencephalogram rhythms are associated with different behaviours. Give some examples of Electroencephalogram rhythms and the behaviour they’re associated with
- A high frequency low amplitude EEG rhythm (Beta rhythm) is associated with alertness and wakefullness
- A low frequency high amplitude EEG rhythm (Delta rhythm) is associated with non-REM sleep or a coma
What are the 2 main ways in which the brain is able to produce synchronous brain rhythms?
- Can be generated by a central clock/pacemaker (thalamus)
- Can be generated by collective behaviour of cortical neurons themselves
Explain how the thalamus is able to produce synchronous brain rhythms
- Thalamus has vast connections to cerebral cortex
- Synaptic connections between excitatory and inhibitory thalamic neurons force each neuron to conform to rhythm of the group
- This co-ordinated rhythm can then be passed down to thalamo-cortical neurons in the cortex
Explain how the collective behaviour of cortical neurons produces a synchronous brain rhythm
- Excitatory and inhibitory interconnections of cortical neurons results in co-ordinated and synchronous activity of the cortical neurons
- This activity can remain local or be passed on to other areas of cortex
What are the functions of brain rhythms?
One hypothesis is that brain rhythms don’t have a function themselves but are instead by-products of the activity of brain circuits
What is sleep?
Sleep is the readily reversible state of reduced responsiveness to, and interaction with, the environment.
What are the different functional states of the brain?
- Wakefulllness
- Non-REM sleep - Body capable of involuntary movement, not accompanied by vivid dreams
- REM-sleep - Body immobilised, vivid dreams
What are the different brain rhythms that are seen during the different functional brain states?
- Wakefullness - alpha, beta and gamma rhythms
- Non-REM sleep - beta and gamma rhythms
- REM sleep rhythms divided into 4 stages:
- Stage 1 - Theta rhythms
- Stage 2 - Spindle rhythms
- Stage 3 - Delta rhythms
- Stage 4 - Delta rhythms (higher amplitude/lower frequency than stage 3)
What physiological changes occur during Non-REM sleep?
- Tempearture decreases
- Heart rate decreases
- Breathing decreases
- Brain energy consumption decreases
What physiological changes occur during REM sleep?
- Temperature decreases massively
- Heart decreases and become irregular
- Breathing decreases and becomes irregular
- Brain energy consumption increases massively (even higher than when we’re awake)
Briefly describe the stages of the sleep cycle
- Sleep cycle icludes 4 different stages - 3 non-REM sleep stages and then REM sleep
- Each night starts out with a period of non-REM sleep
- You then cycle through the first 3 stages of sleep throughout the night with the cycle starting over every 90 minutes
- You cycle through these stages until you shift into REM sleep
What are the theories for why we sleep?
- Restoration - We sleep to rest and recover/prepare to be awake again
- Adaptation - We sleep to protect ourselves and to conserve energy
What happens to the activity of the brain during wakefulness?
- During wakefulness there’s an increase in brainstem activity
- Several sets of neurons increase firing in anticipation of waking up which enhances the wake state
- These neurons include: Cholinergic neurons in basal forebrain, Adrenergic neurons in locus coeruleus and serotonergic neurons in raphe nuclei
- These neurons project to the thalamus and cortex so increase in their activity supresses the rhythmic firing of both of these areas seen during sleep
Explain what happens to the circadian rhythms of humans when all zeitgebers (environmental cues) are gone
- Said to be in a “free-running” state
- This is where the length of the circadian rhythms remains constant but the times at which they are initiated/ended are different to a normal situation
How is the suprachiasmatic nucleus able to synchronise our circadian rhythms with the day-night cycle?
- Specialised photoreceptor cells in the retina that express melanopsin detect changes in illumination
- In response to light these receptors become activated and send signals to the suprachiasmatic nucleus (SCN)
- This inhibits the pineal gland in the hypothalamus from secreting melatonin which induces sleep
