1. AZRA NAHEED MEDICAL COLLEGE
DEPARTMENT OF PYIOLOGY
DR.TAYYABA AZHAR

2. SLEEP
Sleep is defined as unconciousness from which the person can be aroused by sensory or other stimuli.

3. 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.

4. Classification of Brain Waves :
EEG associated with sleep from the highest to the lowest frequency:
Beta waves (ß) The frequency of beta waves range from 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.

5. 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.

6. Features of NREM Sleep

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. Characteristics of sleep
Slow-wave sleep
progressive decrease in spinal reflexes
progressive reduction in heart rate and breathing rate
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

13. 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.

14. Neuronal Centers, Neurohumoral Substances, and Mechanisms That Can Cause Sleep— A Possible Specific Role for Serotonin
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.

15. 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

16. 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.