EEG, Sleep and Circadian Rhythms Flashcards
Where does the process of sleep originate from
The reticular formation of the brain stem
What is the function of the reticular formation
An area that controls the state of consciousness
If brain stem was destroyed at the level of the midpons what would occur
Brain never sleeps
How does the reticular formation promote sleep
Inhibitory impulses to thalamus and higher cortical areas to dampen down activity in cortex and put in state of unawareness
What are many neurones within the reticular formation,
Serotonergic
What is serotonergic
a nerve ending that releases and is stimulated by serotonin
What neurotransmitter is critical for sleep induction
Serotonin
What is serotonin a precursor of
Melatonin
What induces natural sleep
Serotonin
Melatonin
Sleep inducing peptides (isolated from CSF of a different sleep deprived animal)
How is the hypothalamus involved in the induction of sleep
Due to suprachiasmatic nuclei lying just above the optic chiasma creating a 24hr circadian rhythm
What causes the the electrical stimulation of the SCN that promotes sleep
Darkness - when light stops hitting the back of the retina
nerve fibres in the optic nerve pass to SCN
What does the electrical stimulation of the SCN stimulate
The release of melatonin from the pineal gland - which corresponds to the sleepiness in humans
What neurotransmitter does the hypothalamus release thats required for wakefulness
The excretory neurotransmitter - orexin (aka hypocretin)
Active during wake state and stop firing during sleep
What does defective orexin signalling cause
Narcolepsy - suddenly fall asleep
How is the wakefulness cycle sustained for many hours
Excitatory neurons in the Ascending Reticular Activating System (ARAS), are released from Sleep Centres in Reticular Formation stimulating excretory pathways in both CNS and PNS creating a positive feedback loop
What occurs for sleep cycle to occur from wakefulness cycle
Active cells become fatigues causing excretory signals to fade, so inhibitory peptide signals from sleep centres in the reticular formation dominate weakened excretory signal and lead to progression into sleep state
How is sleep cycle overthrown from wakeful cycle
Inhibitory cells fatigue and excretory cells are reinvigorated
What is the two methods to asses level of consciousness in an awake person
Look at their behaviour/alertness/skills /ability
EEG - record patterns of brain activity
What occurs in an EEG
Electrodes placed on scalp to record activity of underlying neurones
What are brain waves from EEG analysed by
Amplitude - size of the wave
Frequency - number of waves per second
Frequency is the most important factor of brain activity so what is the affect of Increased neuronal excitation on it
Frequency increased with neuronal excitation
What are the four main types of brain waves patterns recored on an EEG
Alpha
Beta
Theta
Delta
What causes the various characteristic of wave pattern
Different states of consciousness
What is the characteristics of alpha waves
High frequency and high amplitude
What is the characteristic of beta waves
The highest frequency and low amplitude
What waves are involved in a relaxed awake state
Alpha waves
What waves are a involved in alert wake state
Beta waves
Why do you have a higher amplitude of waves in a relaxed state
Not music info coming into the brain so waves are sync with each other, therefore add together give a larger wave
Why do you have a high frequency and low amplitude in a alert state
Alert state means you have lots of info coming into the brain giving a greater frequency and this means waves become asynchronous and cancel each other out creating a lower amplitude