Sleep

Brain Waves

Electrical recordings from the surface of the brain or even from the outer surface of the head demonstrate that there is continuous electrical activity in the brain.
Both the intensity and the patterns of this electrical activity are determined by the level of excitation of different parts of the brain resulting from sleep, wakefulness,
or brain diseases such as epilepsy or even
psychoses. The undulations in the recorded electrical potentials, are called brain waves,
and the entire record is called an EEG (electroencephalogram).
the waves change markedly between the states of wakefulness and sleep and coma.
In normal healthy people, most waves in the EEG can be classified as alpha, beta, theta, and delta waves, which are shown .
Alpha waves are rhythmical waves that occur at frequencies between 8 and 13 cycles per second and are found in the EEGs of almost all normal adult people
when they are awake and in a quiet, resting state.
Beta waves occur at frequencies greater than 14 cycles per second up to 80 cycles per second. Occur when the awake person’s attention is directed to some specific type of mental activity
Theta waves have frequencies between 4 and 7 cycles per second. They occur in children and in adult during emotional stress and in many brain disorders, often in degenerative brain states.
Delta waves EEG with frequencies less than 3.5 cycles per second. They occur in very deep sleep, in infancy, and in serious organic brain disease.
Alert wakefulness (beta waves)
Quiet wakefulness (alpha waves)
Stage 1 sleep (low voltage and spindles)
Stages 2 and 3 sleep (theta waves)
Stage 4 slow wave sleep (delta waves)
REM sleep (beta waves)


Sleep
Sleep is defined as unconsciousness from which the person can be aroused by stimulation. While coma, which is unconsciousness from which the person cannot be aroused.

Two Types of Sleep.

During each night, a person goes through stages of two types of sleep that alternate with each other. They are called
(1) slow-wave sleep,
(2) rapid eye movement sleep (REM sleep)

Slow-Wave Sleep: in this type of sleep the brain waves are very low frequency

Most sleep during each night is of the slow-wave variety; this is the deep, restful sleep that the person experiences during the first hour of sleep after having been awake for many hours.
This sleep is associated with decrease in blood pressure, respiratory rate, and basal metabolic rate.
Although slow-wave sleep is frequently called “dreamless sleep,” dreams and sometimes even nightmares do occur during slow-wave sleep. The difference between the dreams that occur in slow-wave sleep and those that occur in REM sleep is that the dreams of slow-wave sleep usually are not remembered.

REM Sleep (Paradoxical Sleep): in this type of sleep the eyes undergo rapid movements .
In a normal night of sleep, bouts of REM sleep lasting 5 to 30 minutes usually appear on the average every 90 minutes.
There are several important characteristics of REM sleep:
1. This type of sleep is not so restful, and it is usually associated with dreaming and active bodily muscle movements.
2. The person is even more difficult to arouse by sensory stimuli than during deep slow-wave sleep, and yet people usually awaken spontaneously in the morning during an episode of REM sleep.
3. Muscle tone throughout the body is Depressed.
4. Heart rate and respiratory rate usually become irregular, which is characteristic of the dream state.
5. The rapid movements of the eyes.
6. The brain is highly active in REM sleep.
The electroencephalogram (EEG) shows a pattern of brain waves similar to those that occur during wakefulness. This type of sleep is also called paradoxical sleep because it is a paradox that a person can still be asleep despite marked activity in the brain.


Basic Theories of Sleep:
The brain had a sleeping center (between pons and medulla) and a wakefulness center in the reticular activating system in the brain stem,
passive theory of sleep simply the reticular activating system fatigued during the waking day and become depressed and person go to sleep this is passive theory of sleep its an old theory.
Active theory of sleep that Stimulation of sleeping center of the brain with an active inhibition of the reticular activating system produce sleep.

Sleeping centers

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. stimulation the raphe nuclei in the lower half of the pons and in the medulla. these raphe neurons secrete serotonin,which 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 to the part of the hypothalamus, mainly in the suprachiasmal area
Cycle Between Sleep and Wakefulness
The mechanism for causing the sleep-wakefulness cycle.When the sleep centers are not activated, the reticular activating system are released from inhibition and become active.
Then, after the brain remains activated for many hours, the reticular activating system become fatigued, the sleep-promoting effects of the sleep centers take over, leading to rapid transition from wakefulness back to sleep.
This overall theory could explain the rapid transitions from sleep to wakefulness and from wakefulness to sleep. It could also explain arousal, the insomnia that occurs when a person’s mind becomes preoccupied with a thought.

Physiologic Effects of Sleep

Lack of sleep certainly affect the functions of the central nervous system. Prolonged wakefulness is often associated abnormal behavioral activities.
We can assume that sleep in multiple ways restores both normal levels of brain activity and normal “balance” among the different functions of the central nervous system. This might be likened to the “rezeroing” of electronic analog computers after prolonged use.