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AZRA NAHEED MEDICAL
COLLEGE
DEPARTMENT OF PYIOLOGY
DR.TAYYABA AZHAR
SLEEP
• Sleep is defined as unconciousness from
which the person can be aroused by sensory
or other stimuli.
HOW DO WE MEASURE SLEEP?
• Electroencephalogram (EEG) measures the electrical
changes in the brain.
• The electrodes are placed on the scalp. The wavy lines
recorded by the EEG are called brain waves.
• Electrooculogram (EOG) measures the electrical changes as
the eyes rotate in its socket. The electrodes are placed
either above and below the eye or left and right of the eye.
• Electromyogram (EMG) measures the electrical changes
generated during muscle contraction. The electrodes are
placed under the chin.
• EEG, EOG and EMG are recorded simultaneously and the
patterns of activity in these three systems provide basic
classification for the different types of sleep.
Classification of Brain Waves :
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• EEG associated with sleep from the highest to the lowest frequency:
• Beta waves (ß) The frequency of beta waves range from 13-15 to 60 hertz
(Hz) and an amplitude of 30 microvolt (µV). Beta waves are associated
with wakefulness.
• Alpha waves (a) The frequency range from 8 to 12 Hz and an amplitude of
30 to 50 µV. These waves are found in people who have their eyes closed
and relax or meditating.
• Theta waves :- Frequency in the range of 3 to 8 Hz and amplitude of 50 to
100 µV. These waves are related with memory, emotions and activity in
the limbic system.
• Delta waves (d) It ranges from 0.5 to 4 Hz in frequency and amplitude of
100 to 200 µV.
• Scientists had observed delta waves in deep sleep and in coma patients
because normal and healthy adults will not show large amount of delta
waves. Flat-line trace occurs when no brain waves are present and this is
the clinical sign of brain death.
STAGES OF SLEEP
• Sleep is characterized by two distinct cycles,
• NREM sleep. Non-Rapid Eye Movement Sleep (NREM) is further
classified into 4 stages: Stage 1, Stage 2, Stage 3 and Stage 4.
• Rapid Eye Movement Sleep (REM) sleep Stages 3 and 4 in humans
are homologous to animal sleep stage of slow-wave sleep (SWS).
• A normal human sleep cycle starts with NREM stage 1, stage 2,
stage 3, stage 4 and progresses to REM.
• This cycle is repeated several times throughout the night (between
4 to 5 cycles). The duration for each cycle has been identified
ranging between 60 to 90 minutes. The next section explains the
characteristics of each of the four stages in detail.
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Features of NREM Sleep
STAGE 1
• NREM sleep begins when a person close his eyes,
followed by several sudden sharp muscles contractions
in the legs then relaxation
• As he continues falling asleep the rapid beta waves of
wakefulness are replaced by the slower alpha waves and
soon the slower theta waves start to emerge.
• This is the stage, which is when human get lightest sleep
and could wake up easily external environment.
• Each period of stage 1 sleep generally lasts 3 to 12
minutes.
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STAGE 2
• This is the stage of light sleep in which the frequency of
the EEG decreases and amplitude increases.
• The theta waves of this stage are interrupted by a series
of high frequency waves known as sleep spindles and
they last for 1 to 2 seconds.
• These waves are generated by interactions between
thalamic and cortical neurons.
• During this stage the EEG traces show high amplitude
wave forms called K-complex.
• This is the stage where adults spend the greatest
proportion of about 50% of the total time in sleep each
night. Sleep spindles and K-complex are features of
stage 2 NREM sleep.
STAGE 3
• This is the stage from moderate to true deep
sleep (SWS).
• As delta waves first appear, sleep spindles and
K-complexes occur, but are less common
compared to in stage 2.
• Stage 3 lasts for 10 minutes during the first
sleep cycle and represents only 7% of the total
night’s sleep.
STAGE4
• This is the deepest NREM sleep.
• The EEG trace is dominated by delta waves
and overall neural activity is at its lowest.
• This is also the stage in which children may
have episodes of somnambulism or
sleepwalking and night terrors.
RAPID EYE MOVEMENT SLEEP
• Rapid Eye Movement Sleep (REM) or paradoxical sleep
constitutes 20-25% of total sleeping time.
• Over the course of a night’s sleep, a person will experience
4 to 5 periods of REM sleep.
• EEG recording of neural activity during REM shows almost
the same tracing as to that during waking hours.
• There are no dominating brains waves during this stage of
sleep. REM sleep is characterized with rapid movement of
the eyes in its sockets, near-total muscle paralysis and
changes in breathing and heart rates.
• Most people will wake up easily during this period if there
are any external disturbances. This is because REM sleeps
happens to be the period of very light sleep.
Characteristics of sleep
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Slow-wave sleep
progressive decrease in spinal reflexes
progressive reduction in heart rate and breathing rat
reduced brain temperature and cerebral blood flow
increased hormone secretion (e.g. growth hormone)
synchronised cortical activity
REM sleep
spinal reflexes absent
rapid eye movements bihind closed eyelids
increased body temperature and cerebral blood flow
desynchronised cortical activity
dreams
Basic Theories of Sleep
• Sleep Is Believed to Be Caused by an Active Inhibitory
Process.
• An earlier theory of sleep was that the excitatory areas of
the upper brain stem, the reticular activating system, simply
fatigued during the waking day and became inactive as a
result. This was called the passive theory of sleep.
• An important experiment changed this view to the current
belief that sleep is caused by an active inhibitory process:
• it was discovered that transecting the brain stem at the
level of the midpons creates a brain whose cortex never
goes to sleep. In other words, there seems to be some
center located below the midpontile level of the brain stem
that is required to cause sleep by inhibiting other parts of
the brain.
Neuronal Centers, Neurohumoral Substances,
and Mechanisms That Can Cause Sleep—
A Possible Specific Role for Serotonin
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Stimulation of several specific areas of the brain can produce sleep with
characteristics near those of natural sleep. Some of these areas are the following:
1. The most conspicuous stimulation area for causing almost natural sleep is the
raphe nuclei in the lower half of the pons and in the medulla.
These nuclei are a thin sheet of special neurons located in the midline. Nerve fibers
from these nuclei spread locally in the brain stem reticular formation and also
upward into the thalamus, hypothalamus, most areas of the limbic system, and even
the neocortex of the cerebrum.
TIn addition, fibers extend downward into the spinal cord, terminating in the
posterior horns where they can inhibit incoming sensory signals, including pain. It is
also known that many nerve endings of fibers from these raphe neurons secrete
serotonin.
When a drug that blocks the formation of serotonin is administered to an animal, the
animal often cannot sleep for the next several days.
Therefore, it has been assumed that serotonin is a transmitter substance associated
with production of sleep.
• 2. Stimulation of some areas in the nucleus of
the tractus solitarius can also cause sleep.
• This nucleus is the termination in the medulla
and pons for visceral sensory signals entering
by way of the vagus and glossopharyngeal
nerves
• 3. Stimulation of several regions in the
diencephalon can also promote sleep,
including
• (1) the rostral part of the hypothalamus,
mainly in the suprachiasmal area, and
• (2) an occasional area in the diffuse nuclei of
the thalamus.