The Physiology of Sleep Flashcards
Define Sleep
a natural period state of rest for the mind and body, in which the eyes usually close and consciousness in completely or partially lost, so that there is a decrease in bodily movement and responsiveness to external stimuli
Sleep Deprivation can lead to:
- grumpiness
- grogginess
- irritability
- forgetfulness
- language, memory, planning and
sense of time are severely affected
How do we measure sleep?
- questionnaire
- physiological measurements EEG
Analysis of Sleep: Questionnaire:
- eg do you feel your sleep is not
refreshing or restful - results can be limiting due to
increased error due to bias
Analysis of Sleep: Physiological Measurements:
- more complex approach
- eg brain waves, neurochemicals,
sleep models, pharmacology - results are limited by methods
used, mostly free from bias and
are reproducible
EEG stands for
Electroencephalography
EEG: Method:
involves the recording of a gross average of electrical potentials of the cells and fibers in the brain areas closes to each electrode attached to the scalp
EEG: Basic Principle:
- neurons generate electrical action
potentials - the firing of many neurons creates
a large electrical field in particular
brain regions
Generation of small fields in pyramidal cells:
insert diagram
What are the 2 basic requirements for signal detection?
- a whole population o fneurons
must be active in synchonicity to
generate a large enough electrical
field at the level of the scalp - this population of neurons must
be aligned in a parallel orientation
so that they summate rather than
cancel out
The amplitude of EEG signals depends upon:
- the synchronous activity of
underlying neurons - number of active cells, total
amount of excitation, timing of
activity are key contributors
What type of cells generate synchronous rhythmns?
Thalamic cells have a set of voltage-gated ion channels that allow each cell to generate rhythmic, self-sustaining discharge patters even in the absence of external inputs
the rhythmic activity of each thalamic pacemaker neuron then becomes synchronised with many other thalamic cells through cellular and chemical communication
Function of Brain Rhythms?
- sensory input travels to thalamus,
then directed to functional area of
cortex - meaningless by-product of
feedback circuits and connections
EEG Recordings:
- electrical potentials are recorded
from either the entire skull surface
or from specific points - electrical potentials are recorded
as traces - increased, synchronised activity is
displayed as a larger amplitude
than the baseline recording
Interpreting Sleep Through EEGs:
- EEG recorded whilst asleep
- observes monitored behavioural
changes during sleep - traces obtained were analysed
from amplitude and frequency of
wave patterns
EEG:
- flat line
- peak
- trough
Flat line = half the neurons recorded are firing, half are inhibiting
Peak = all are firing in that area
Trough = none are firing in that area
Whilst sleeping, heart rate, breathing rate and brain activity
decrease
Major behavioural changes whilst sleeping:
- lack of gross movement (large
amounts of muscle movement) - presence of Rapid Eye Movement
(REM) cycles throughout a period
of sleep
Correlating EEG with Behaviour:
All are different stages:
insert slide
EEG:
insert figure
How many stages in sleep?
- 4 stages non-REM sleep (N1,2,3)
- 1 stage REM sleep
Sleep: N1:
- non-REM sleep
- dominated by irregular, jagged,
low voltage waves - brain activity is high but will start
to decline
Sleep: N2:
- non-REM sleep
- sleep spindles
- K-complexes
Sleep: N2: Sleep Spindles:
- 12-14Hz burst for at least 500msec
- generated by oscillating
interactions between cells in the
thalamus and the cortex
Sleep N2: K-Complexes:
- sharp, high amplitude positive
wave - followed by a smaller, slow,
negative wave - occurs randomly and in response
to auditory stimuli
Sleep: N3:
- Non-REM
- delta waves
Sleep: N3: Delta Waves:
- slow, large amplitude waves
- neural activity is highly
synchronised
Sleep: Stage 4 N3:
- Non-REM
- increased delta wave activity
- stage 3 and 4 are known together
as slow-wave sleep (SWS) - sleepwalking, nightmares, bed
wetting can occur at this stage of
sleep
Sleep: REM Stage (5):
- rapid eye movement
- irregular, low voltage fast waves,
similar to those in stage 1 of non-
REM sleep - increased brain activity, may be
associated with a state of
dreaming
Describe the waves on EEG when awake with eyes open.
low amplitude = no synchronicity, all neurons are doing different things
beta waves in all stages
high frequency low amplitude = brain is active
Describe the waves on EEG when awake with eyes closed.
high frequency similar to awake with eyes open = brain is active
higher amplitude than awake with eyes open = more synchronicity (visual neurons)
In Non-REM sleep, neurons become more
synchronised (larger amplitude, lower frequency)
In REM sleep, neurons are
synchronised but very active as dreaming
Newborn babies wake every 1.5 hours because
struggle with transition from light sleep in non-REM to deep REM sleep
How long does the entire sleep cycle last?
- 90-120 minutes
- first cycle starts at stage 1
- subsequent cycles will start at
stage 2 and continue through to
REM sleep every 90 - 110 minutes
REM Sleep: Physiological Changes:
- postural muscles become more
relaxed = deep REM sleep - heart rate, bp, rr are more variable
than other stages of sleep - increased blood supply to
reproductive organs
Influences of Benzodiazepines on Sleep:
- bind to gaba a receptors
- Cl- channel
- hyperpolarises cells
- modulator not a ligand
- allows Cl- channel to open for longer
increases the length or non-REM sleep but decreases REM sleep so will decrease effects of sleep
EEG Limitations:
- scalp electrodes are not sensitive
enough to pick up individual action
potentials - can not distinguish between
excitatory, modulatory or
inhibitory activity - limited anatomical specificity
compared with other imaging tools
such as fMRI
Other physiological systems that contribute to sleep:
- hormone systems
- melatonin and cortisol rhythms
- melatonin increases during sleep
- cortisol decreases at the start and
increases at the end
Examples of Circadian Regulation:
cortisol high during the day, low at night
when put in light at night still persist but slightly altered
Parasomnias:
- disruptive sleep related disorders
Non-REM Parasomnias:
- sleep walking; still asleep but
exhibit limited awareness and
repsonsiveness to their
surroundings
- night terrors: often scream in their sleep, though most are not responsive to outside stimuli and will have no recollection of the source of their terror upon waking
REM Parasomnias:
- unusual vocalisations or
movements during REM sleep,
often as a reaction to a dream
Circadian and Peripheral Cycle:
central pacemaker; when light positive signal, dark no signal
synchronises all hormonal systems
peripheral oscillators synchronise directed by the central pacemaker
jet lag is the lag between the central and peripheral
