sleep Flashcards
how do we measure brain rhythmicity?
an electroencephalogram (EEG)
what does an electroencephalogram (EEG) involve?
non invasive electrodes placed on standard positions on the head and connected to amplifiers and a recording device
what are electroencephalogram (EEG)’s used for?
diagnose certain neurological disorders
e.g. seizures in epilepsy
what does an electroencephalogram (EEG) measure?
the combined activity of a large number (1000s) of similarly orientated neurons
- summed post-synaptic activity
- requires synchronous activity across groups of cells
what does the amplitude of an EEG signal depend on?
how synchronous the activity of the neurons is
what happens when a group of cells is excited?
the tiny signals sum to generate a large surface signal
-the same amount of excitation can occur, but at irregular intervals, resulting in a small summed signal
what do EEG rhythms correlate with and how are they categorised?
- correlate with states of behaviours
- categorised by their frequency range
alertness and waking has what EEG rhythm?
high-frequency low-amplitude
non-dreaming sleep or coma has what EEG rhythm?
low-frequency high-amplitude
2 ways synchronous brain rhythms are generated?
pacemaker
-synchronous rhythms led by a central clock/pacemaker (e.g. thalamus)
collective behaviour
-synchronous rhythms arise from the collective behaviour of cortical neurons themselves
how can the thalamus act?
as a pacemaker
pacemaker behaviour, how is each individual thalamic neuron forced to conform to the rhythm of the group?
synaptic connections between excitatory and inhibitory thalamic neurons
the thalamus passes coordinated rhythms onto where?
the cortex by thalamocortical axons
a relatively small group of centralised thalamic cells can do what?
can compel a much larger group of cortical cells
with collective behaviour, how does synchronous coordinated activity happen in the neurones?
excitatory and inhibitory interconnections of neurons
-can remain localised or spread to larger regions of the cortex
name the 3 functional states of the brain
- Wakefulness
- non-REM sleep
- REM sleep
describe non-REM sleep
body capable of involuntary movement, rarely accompanied by vivid, detailed dreams
- “Idling brain in a moveable body”
- low frequency high amplitude
- occasional voluntary movement
- logical repetitive thoughts
describe REM sleep
body immobilised, accompanied by vivid, detailed dreams
- “An active, hallucinating brain in a paralysed body”
- Low-amplitude, high frequency - just like when awake
- vivid bizarre thoughts
- muscle paralysis
explain what happens to temperature, heart, rate, breathing during non-REM and REM sleep
temperature, heart rate and breathing all decrease
- temp decreases more in REM sleep
- HR and breathing decrease more in non-REM sleep
brain energy consumption in REM vs non-REM sleep
brain energy consumption decreases in non-REM sleep
INCREASES massively in REM sleep
what does each night begin with and what happens as night progresses?
- each night begins with a period of non-REM sleep
- as night progresses, there is a shift from non-REM to REM sleep
how often are sleep cycles repeated throughout the night?
every 90 minutes
purpose of sleep?
- restoration and adaptation
- sleep means we can rest and recover
- sleep means we can protect ourselves and conserve energy
what happens during wakefulness?
there is an increase in brainstem activity, and several sets of neurones in increase their rate of firing in anticipation of waking to enhance the wake state
-ACh, 5-HT, NA and histamine
in waking where do the ACh, 5-HT, NA and histamine synapse to?
synapse directly to brain regions including the thalamus and cerebral cortex
the increase in excitatory activity upon waking has what effect?
suppresses rhythmic forms of firing in the thalamus and cortex present during sleep
during sleep, what happens to brain stem activity?
decreases
-rhythmic firing from thalamus blocks the flow of sensory information up to the cortex
what happens to several sets of neurones during sleep?
decrease their rate of firing
-Ach, 5-HT, NA
cholinergic neurons in the pons…
…..increase their rate of firing to induce REM sleep
other sleep promoting factors?
- adenosine
- nitric oxide
- inflammatory factors
- melatonin
role of adenosine in sleep?
- DNA, RNA, ATP building block
- adenosine receptor activation decreases HR, SM tone and respiratory rate - decrease in BP
what do adenosine receptor antagonists, like caffeine, promote?
promote wakefulness
role of nitric oxide in sleep?
- a potent vasodilator
- decreases SM tone - decrease BP
- stimulates adenosine release
role of inflammatory factors in sleep?
- consequence of infection
- cytokines (e.g. interleukin-1) stimulates the immune system to fight infections
- Interleukin-1 levels promote non-REM sleep
role of melatonin in sleep?
- secreted by the pineal body at night, induces sleep
- over-the-counter medication for symptoms of jet-lag
- initiates and maintains sleep – unclear role in natural sleep wake cycle
circadian rhythms
daily cycles of daylight and darkness
-based on 24hr clock
what is the suprachiasmatic nucleus (SCN)?
- small hypothalamic nucleus innervated by the retina
- synchronises circadian rhythms with the daily light-dark cycle
if the SCN is inhibited does it abolish sleep?
no
is the SCN stimulated by rods and cones?
no, specialised photoreceptor cells expressing the photopigment melanopsin
how are photoreceptors expressing melanopsin affected by light and where do they project to?
- slowly excited by light, detect changes in luminosity
- project directly to SCN, inhibiting the melatonin production by the pineal gland
