Lecture 10 : Sleep Flashcards
Sleep is
a natural, reversible, recurrent
state of reduced responsiveness to external
stimulation that is accompanied by complex
and predictable changes in physiology
Sleep is characterized by (4):
-Altered consciousness.
-Minimal motor & sensory activity.
-Specific pattern of brain activity.
-Reduced interactions with the external world.
Electroencephalography (EEG) is
an electrophysiological monitoring method to
record electrical activity of the brain, with electrodes placed along the scalp
EEG measures
voltage currents resulting from electrical ponetials (EPSP & IPSP)
generated by cortical neurons, reflecetd in the EEG as electrical waves
EEG as electrical waves:
Brain
waves (α, β, θ, δ waves)
EEG is used to (3):
-Monitor sleep stages & diagnose sleep disorders (Polysomnography).
-Diagnose neurological disorders (e.g. epilepsy, encephalopathies, stroke…).
-Monitor coma, brain death and anesthesia level.
Beta range of Hertz
15-30 Hz
Beta wave : Amplitude and Frequency
Low amplitude
High frequency
Beta waves are characterized by:
Highly alert, eyes open
Alpha range Hertz range:
9-14 Hz
Alpha waves: Amplitude and Frequency:
Low amplitude and High Frequency
Alpha wave characterization:
Low amplitude and High frequency
Theta range of brain waves:
5-8 Hz
Theta waves amplitude and frequency:
intermediate amplitude and intermediate frequency
Theta waves can be characterized by what state
drowsy
Delta waves: Hz range
0.5-4Hz
Delta waves: amplitude and frequency:
High amplitude and low frequency
Delta waves characterized by what state:
Deep sleep
Wakefulness: Composed of 2 states:
(1) Active wakefulness
(2) Resting wakefulness
Active wakefulness:
Eyes open, active state, Beta waves
Resting wakefulness:
Eyes closed, relaxed state, Alpha waves
Sleep composed of two states:
(1) Non-REM sleep (4 stages)
(2) REM sleep
Non-rapid eye movement sleep (non-REM): composed of
4 stages
In non rem sleep, what are the two stages of light sleep?
Stage 1 and Stage 2
In non - REM sleep, deep sleep is what stage?
Stage 3 and Stage 4
Wakefulness:
: Beta & Alpha waves: high EEG frequency (9–30 Hz) & low EEG
amplitude (∼30 µV).
Stage I:
Theta waves: intermediate EEG frequency (5–8 Hz) & intermediate EEG
amplitude (50 – 100 µV).
Stage II:
Theta waves and SLEEP spindle: high EEG frequency (11–15 Hz) & low
EEG amplitude (50 µV) and K-Complex (isolated slow wave).
Stage III & IV:
SLOW WAVES (delta waves): low frequency (0.5 to 4 Hz) & high EEG
amplitude (100 – 150 µV).
REM sleep:
Beta & Alpha waves: high EEG frequency (9–30 Hz) & low EEG
amplitude (∼30 µV). The same as in Wakefulness.
Electroencephalogram (EEG) shows:
Typical brain waves of sleep and wakefulness
REM sleep is also known as:
Paradoxical sleep
REM sleep is characterized by (5) :
-High EEG frequency (10-30Hz)
- low EEG amplitude (30 uv)
-Rapid eye movements (REM) while the eyelids are closed
-Transient muscle activity (i.e. jerky muscle activity)
-Predominance of dreams
Sleep occurs in __
cycles
The period of each cycle is approximately:
90 minutes (1h and 1.5 h) in human (4-5 cycles/night)
non-REM sleep is __ at the begginning of the sleep but as the sleeper becomes more rested through the night the duration of non-REM __
non-REM sleep is LONGER at the BEGINNING of the sleep but as the sleeper becomes more rested through the night, the durations of non-REM DECREASES
REM sleep is __ at the beginning but becomes __ at the end
REM sleep is short at the beginning but becomes long at the end
During WAKEFULNESS, the cerebral cortex and thalamus are kept:
EXCITED by neurons of the ASCENDING AROUSAL SYSTEM located at the subcortical level
complete slide 11
During wakefulness: cortical neurons discharge APs with:
FAST and IRREGULAR patterns (i.e. not at the same time), which results in a LOW AMPLITUDE and FAST FREQUENCY EEG –> DESYNCHRONIZED EEG (i.e. beta and alpha waves)
The arousal system neurons stimulate
also:
MOTOR NEURONS in the spinal cord to keep a HIGHER MUSCLE TONE during wakefulness
Non-REM sleep:
Synchronized Brain Activity
During Non-REM sleep: INHIBITORY NEURONS (mainly GABA) located in the
Hypothalamus (VENTROLATERAL PREOPTIC NUCLEUS, VLPO) INHIBIT the
neurons of the AROUSAL SYSTEM to
promote sleep.
Non-REM sleep:
Synchronized Brain Activity: The cortex and thalamus are:
no longer excited by the neurons of the arousal system or by sensory inputs (i.e. disconnected from the external world)
Non-REM sleep:
Synchronized Brain Activity: Cortical and thalamic neurons:
switch to
a SLOW & RHYTMIC discharge patterns
(i.e. discharge all at the same time),
which results in a HIGH AMPLITUDE and
SLOW FREQUENCY EEG activity:
‘SYNCHRONIZED EEG’ activity (i.e. slowwaves sleep).
REM sleep:
The ascending cholinergic activation
During REM sleep, the brainstem ACETYLCHOLINE NEURONS are RE-ACTIVATED (released from VLPO inhibition) and send their ASCENDING fibers to excite the thalamus and cortex, which results in fast cortical activity (i.e. DESYNChrONIZED EEG activity) similar to waking state
REM sleep:
The descending cholinergic control of
muscle atonia
During REM sleep, the brainstem ACETYLCHOLINE NEURONS are RE-ACTIVATEd and send also their DESCENDING fibers to EXCITE medullar and spinal inhibitory interneurons, which in turn inhibit spinal motor neurons. The inhibition of motor neurons leads to a significant decrease of muscle tone, MUSCLE ATONIA
Most of dreams occur during
REM sleep.
The sleep-wake cycle is regulated
by two processes:
(1) Process S (Sleep Homeostatic)
(2) Process C (Circadian Rhythm)
Process S (Sleep Homeostatic):
sleep pressure (i.e. sleep need)
accumulates across the day:
➢ The more the person stays
awake, the more the sleep
pressure incerased.
➢ The more the person stays
asleep, the more the sleep
pressure decerased.
Process C (Circadian Rhythm):
biological clock, under the control of the hypothalamus:
➢ Follows the light-dark cycle.
➢ Releases sleep-related
hormones (e.g. Melatonin).
sleep is
important for
physical, cognitive and psychological
well-being (i.e. sleep is a vital function)
Sleep Functions (8)
- Resting of different parts of the body.
- Restore natural balances among the neuronal centers.
- Acceleration of neural maturation (need of sleep for youth).
- Facilitation of learning and memory (neuronal plasticity).
- Clearance of metabolic waste products generated by neural
activity in the awake. - Conservation of metabolic energy.
- Hormonal regulation.
- Speed up recovery from injuries.
Insomnia:
Sleep deficiency characterized by a perceived INABILITY TO FALL AND REMAIN ASLEEP at
night. Sometimes, it may not represent a true inability to sleep (paradoxical insomnia = sleep state
misperception).
paradoxical insomnia
sleep state
misperception
Sleep apnea:
Sleep-related BREATHING DISORDER characterized by repetitive pauses in breathing or
periods of shallow breathing, often associated with snoring. It is caused by a collapse of mouth muscles
on the upper airway during sleep. It causes blood O2 desaturation and frequent awakenings, which
disrupt sleep.
Hypersomnia:
Sleep disorder characterized by excessive daytime sleepiness. It is a failure in the brain
mechanisms that are responsible to maintain arousal during the day.
Narcolepsy:
Sleep disorder seen in the form of SUDDEN REM SLEEP ONSET from wakefulness (sleep
atttacks) and EXCESSIVE DAYTIME SLEEPINESS. It is often associated with CATAPLEXY (muscle paralysis)
following a emotional reaction (e.g. fear, laugh). Caused by the LOSS OF OREXIN NEURONS in the
hypothalamus
Sleepwalking (Somnambulism):
Sleep disorder characterized by a partial arousal (with low
consciousness) from Non-REM sleep and performing activities that are usually performed during
wakefulness (e.g. walking out of the room, eating, driving, homicide…). A total amnesia of the event
(i.e. do not recall the event).
REM Sleep Behaviour Disorder (RBD):
Sleep disorder characterized by excessive motor activity
during REM sleep due to the loss of REM sleep atonia. Patients act out the contents of their dreams.
RBD is often a precursor of neurodegenerative diseases (e.g., Parkinson’s, Lewy body dementia…).
