EEG, Sleep and Circadian Rhythm Flashcards
Where is it suspected that the active inhibitory processes that lead to sleep originate?
- In the reticular formation of the pons
- If the brainstem is destroyed at the mid pons, the brain loses the ability to sleep. Probably originates from below this level
How is release of melatonin controlled by the hypothalamus?
- The suprachiasmatic nuclei (SCN) of the hypothalamus inhibits the pineal gland when exposed to light, and therefore inhibits melatonin release
- Darkness corresponds to decreased SCN activity and therefore increased melatonin release by the pineal
Where is melatonin made and released from?
The pineal gland
Which hormone facilitates SCN inhibition of the pineal gland?
- Orexin (released by hypothalamus during bright hours)
- AKA hypocretin
What is narcolepsy?
The condition of being unable to regulate sleep appropriately
- The narcoleptic patient will fall asleep at inappropriate times and often have daytime drowsiness
- Usually due to inadequate orexin (hypocretin) production
Likely reason that serotonin is necessary for sleep induction?
- Serotonin is a precursor to melatonin in melatonin production
- Serotonin Selective Reuptake Inhibitors can treat sleep disruption, act to increase serotonin levels in synapse
What does EEG stand for? What is it used to record?
- Electroencephalogram
- Records electrical activity in the brain
Main characteristics of an EEG wave?
- Amplitude
- Frequency (increases with neuronal excitation)
What are the four main types of EEG waves?
- Alpha
- Beta
- Theta
- Delta
In a relaxed, awake state what sort of EEG waves are seen?
Alpha waves
- High frequency, high amplitude
In an alert, awake state what sort of EEG waves are seen?
Beta waves
- High frequency, low amplitude waves.
- Waves are asynchronous because brain is doing so much at once that opposing polarities of signals cancel eachother out and are not recorded
Which waves are common in children and during times of emotional stress/frustration?
- Theta waves
- Low frequency, varying amplitude
Which waves only occur during sleep?
Delta waves
- Low frequency and high amplitude
5 stages of sleep and brief description of each?
- Stage 1: low frequency theta waves, light sleep.
- Stage 2: eye movements stop, slower frequency. Clusters of rhythmic waves (sleep spindles) on EEG
- Stage 3: high amplitude, v slow delta waves. Sleep spindle activity declines
- Stage 4: Exclusively delta waves (stage 3&4 known as deep sleep, hard to rouse from)
- REM sleep: rapid eye movements, dreams occur here
How does amplitude vary with sleep stages?
Larger amplitudes associated with deeper sleep
How does REM sleep look on an EEG?
Fast waves, quite similar to the awake state
- Desynchronized, high frequency, low amplitude
What is the most restful type of sleep and when does it occur?
Deep sleep
Occurs in the first hours of sleep, associated with drop in vascular tone (BP) and metabolic rate
After the initial S-wave sleep of stages 3 and 4 what occurs?
A gradual awakening towards stage 1, but not the initial stage 1 - instead REM sleep
Characteristics of REM sleep?
- Dreams occur
- Eye muscles move rapidly, pons inhibits other skeletal muscles
- HR/RR become irregular, brain metabolism increases
- Difficult to arouse an individual from REM sleep
- Whenever deprived of REM sleep there is a catch up period during next sleep
What behaviours do sleep deprived subjects demonstrate?
- Impaired cognitive function
- Impaired physical performance
- Sluggishness
- Irritability
What are some of the important functions sleep supports?
- Neuronal plasticity
- Learning and memory
- Cognition
- Clearance of waste products from CNS
- Conservation of whole body energy
- Immune function
How does sleep change as an individual ages?
- Total sleep time declines drastically over a lifetime
- REM sleep percentage also decreases (from about 50% in infant, to 25% in an adult, may be absent in elderly)
5 common sleep disorders?
- Insomnia
- Nightmares
- Night terrors
- Somnambulism
- Narcolepsy
How is insomnia defined? What are the two types?
- Chronic inability to obtain the necessary amount of quality sleep to maintain daytime behaviour
- Chronic - usually no identifiable cause
- Temporary - in response to pain etc. Usually short lived
