EEG, Sleep and Circadian Rhythms Flashcards
Explain the theory of sleep?
1) Sleep occurs due to active inhibitory processes that originate in the pons
2) Destruction of brainstem at level of mid-pons creates a brain that never sleeps, so something below this must be actively sending inhibitory impulses to the cortex
3) Activity originates in the reticular foramen (evidence suggests) of the brainstem, which is closely associated with controlling state of consciousness
4) Sends projections to the thalamus and higher cortical areas
What part of the hypothalamus does evidence suggest is involved in sleep?
Hypothalamus and its suprachiasmatic nuclei (SNC) are involved in inductino of sleep
What does SCN stand for?
Suprachiasmatic nuclei
What does the SNC inhibit the release of with its 24 hour circadian rhythm?
Melatonin
What are the inhibitory neurons in the SCN stimulated by?
Light and act to inhibit the pineal gland, darkness therefore corresponds with decreased activity in the SCN and increased melatonin release and feelings of sleepiness
What is melatonin produced by?
Pineal gland
What is the circadian rhythm?
24 hour cycle in physiological processes of living beings
What is the circadian rhythm of melatonin release likely linked to the inhibition of?
Orexin
What is orexin?
Excitatory neurotransmitter released from hypothalamus required for wakefulness
Are orexin neurons active during the waking state or when asleep?
During the waking state and stop firing during sleep
How does decreased activity of SCN impact melatonin release and orexin?
Decreased orexin
Increased melatonin
What does defective orexin signalling cause?
Narcolepsy where the individual will suddenly fall asleep sometimes even when they are talking
What is the relationship between serotonin and sleep?
Many neurons within reticular foramen are serotonergic
Drugs that block serotonin formation inhibit sleep suggesting serotonin must be crucial to sleep induction
What does assessing the level of consciousness in an awake person involve?
Look at behaviour, general alertness, speech patterns, speech contents, reading, writing and calculating skills
Spell words backwards or count backwards
Record patterns of brain activity with electroencephlogram (EEG)
What does EEG stand for?
Electroencephalogram
What is an electroencephalogram (EEG)?
Uses electrodes placed on scalp to record brain activity of underlying neurons, showing wave patterns that reflect the electrical activity of the brain
What can the waves produced by an EEG be analysed by?
Amplitude (the size of the wave)
Frequency (the number of waves per second)
What is the range of amplitude of brain waves on an EEG?
From 0-200uV
What is the range of frequencies of brain waves on an EEG?
1 to 50+
How does frequency and amplitude of brain waves change with neuronal excitation?
Frequency - increased with neuronal excitation
Amplitude - decreases with neuronal excitation
What are the four main types of wave patterns seen on an EEG?
Alpha
Beta
Theta
Delta
What are EEG waves characterised by in relaxed, awake state?
High frequency
High amplitude
this is termed alpha waves
What are EEG waves characterised by when in alart, awake state?
Even higher frequency waves than alpha
Low amplitude asynchonous waves (due to brain doing many things at once so opposing polarities cancel each other out and do not get recorded on EEG)
this is termed beta waves
What is the amplitude and frequency like of alpha waves?
High amplitude
High frequency
What is the amplitude and frequency like of beta waves?
Low amplitude
Even higher frequency than alpha waves
What is the amplitude and frequency like in theta waves?
Low frequency
Enourmous variation in amplitude
Who are theta waves common in?
Children during times of emotional stress and frustration in adults
Also occur duing sleep in both adults and children
What is the amplitude and frequency like of delta waves?
Very low frequency
High amplitude