sleep physiology - dr.ebtehag

8/3/2019 Sleep Physiology - Dr.ebtehag

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SLEEP physiologyby

Abeer El-Emamass. Prof. Physiology



EEGIt’s a simple ,painless neurological procedure in

which the brain’s electrical activity is recorded

as wave patterns and printed on paper or

recorded in a computer .



Brain cells communicate with each other byproducing tiny electrical impulses. In an

EEG, this faint electrical activity is measuredby putting electrodes on the scalp.

There are 4 types of EEG waves:



AppearsLocationFrequency (Hz) Types

•Relaxed persons

with closing theeyes .

The parieto-

occipital region .

8 – 13

Higher inamplitude ofabout 50uV

Alpha

(Berger’swave).

•Alert or workingstate.

•Active, busy oranxious thinkingand activeconcentration.

On both sides ,but most evidentfrontally .

12 – 30Lower inamplitude

Beta



Appearslocation Frequency (Hz) Type

•In adults : in verydeep sleep.

•In infancy.

Frontally in adultsPosteriorly in

children

1-3/sec

It’s the slowest

wave with a highamplitude.

Delta

•Normal in

children•Deep relaxation

Found in parietal

and occipital regions

4 – 7Theta



THE AROUSAL OR ALERTING RESPONSE

This is an EEG response that occurs when the subject

becomes alert (e.g. on opening his eyes or when solving aproblem). The synchronized alpha rhythm is replaced byrapid irregular low-voltage beta waves It representsbreaking up of the synchronized neuronal alpha activity, so

it is also called alpha block or desynchronization.



oHow the test is performed :-



SLEEP

Sleep is a state of physiological loss of consciousness fromwhich a subject can be aroused by an appropriate stimuli.



sleep

slow-wave

sleep

rapid eye

movementsleep

NREM REM



Non-REM SLEEP

* Characters of NREM sleep:

- Breathing is slow

-Blood pressure falls

- decrease in basal metabolic rate

-Little or no body movement

-Decrease in heart rate

-Decrease in the peripheral vascular tone

-dreams do occur but they are not consolidated in thememory, therefore not remembered.



CLASSIFICATION

- NREM sleep has traditionally been considered to bedivided into 4 stages depending on EEG pattern

-During wakefulness with closed eyes and relaxed mindthe alpha waves of EEG appear. Passage fromwakefulness to non-REM sleep is characterized byprogressively slower frequencies and higher voltage

activities in the EEG.



Stage I: Theta waves start to appear Stage II: This is characterized by sleep spindles superimposed on the

theta waves. Stage III: EEG starts to show slower delta waves Stage IV: stage of deep sleep, delta waves become more prominent withlow frequency and high amplitude.(If the sleeper is a sleepwalker thisactivity will begin in this phase, Bodily functions decline to the deepest

possible state of physical rest



Rapid eye movement sleep

REM sleep is a type of sleep in which the brain is quite active.

However, the brain activity is not channeled in the proper directionfor the person to be fully aware of his or her surroundings, and

therefore the person is truly asleep.

This type occurs in episodes of 5-30 minutes, which recur about

every 90 minutes



Muscle tone throughout the body is exceedingly depressed, indicating

strong inhibition of the spinal muscle control areas by cluster of peri-

locus cerulous neurons. Despite the extreme inhibition of theperipheral muscles, irregular muscle movements do occur.

Heart rate and respiratory rate usually become irregular, which is

characteristic of the dream state.

There is a reduction in homeostatic mechanisms such as decreasein response of respiratory system to changes in blood CO2.



It is usually associated with active dreaming that is later remembered

The eyes show rapid eye movements and EEG shows activity

similar to the waking state (beta waves with block of slow

waves).

The brain is highly active in REM sleep, andoverall brain metabolism may be increased asmuch as 20 per cent.



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.

This type of sleep is often known as "paradoxical sleep" because

it is a paradox that a person can still be asleep despite the marked

activity in the brain.



In a normal night of sleep, bouts of REM sleep

lasting5 to 30 minutes usually appear on theaverage every90 minutes.

accounts for 20%–25% of totalsleep time in most human adults.



8 hours of sleep = 4 Cycles.

Sleep Cycle

the sleep cycle consists of one episode of NREM followed by REM sleep this cycle isrepeated 4-6 times every night

M h i f l



Mechanism of sleep

Brain centers that initiate and control sleep wake cycles are mainly located in the brainstem and hypothalamic areas. The most important of these areas are

I. Arousal centers

Part of the RAS and descending pathwasy from cerebral cortex (midbrain reticularformation)- posterior hypothalamus- (mediated by histaminergic neurons), therefore,blockage of histaminergic outputs with antihistaminic drugs promotes sleep.

II. Sleep promoting centers

Ventrolateral preoptic nucleus in anterior hypothalamus (VLPO) and Adjecent basal

forebrain, these areas become active during sleep and use inhibitory neurotransmittersGABA and galanin to inhibit arousal centers



Slow wave sleep

Several centers contributs to non-REM sleep

- Raphe nucleus in pons and medulla (secret serotonin at their ending)- Meduallary synchronzing zone in reticular formation of the medulla at thelevel of nuclus of tractus solitarius

- anterior hypothalamus and Adjecent basal forebrain,



Raphe nucleus in pons and medulla

These nuclei are a thin sheet of special neurons located in the midline. Nervefibers from these nuclei spread locally in the brain stem reticular formationand also upward into the thalamus, hypothalamus, most areas of the limbicsystem, and even the neocortex of the cerebrum. In addition, fibers extenddownward into the spinal cord, terminating in the posterior horns where theycan 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 ananimal, the animal often cannot sleep for the next several days. Therefore, ithas been assumed that serotonin is a transmitter substance associated withproduction of sleep.



Genesis of REM sleep

The mechanism that trigger REM sleep is is located in:

- Noradrenergic neurons from locus cerulous and serotonergic raphe neurons

as well as histaminergic neurons in the posterior hypothalmus; inhibit REMon cholinergic cells and stop REM sleep.

- cholinergic neurons from pontine reticular formation have extensive upward

projection activate many areas of the brain.However, this activation is channeled through different pathways from those

used by RAS for activation of the brain during wakefulness.



Circadian rhythm

The suprachiasmatic nucleus (SCN) of the hypothalamus sends impulsesto ventrolateral preoptic area (VLPO) of hypothalamus and provides the

transition between sleep and wakefulness



Adenosine; act to promote sleep, as suggested by thestimulant action of caffeine which blocks adenosine

receptors

Serotonin; can cause suppression of REM sleep

Orexin; is a neuropeptide in the anterolateralhypothalamus it stimulates wakefulness centers and its

deficiency causes narcolepsy

Acetyl choline; Acetylcholine is released from nerveterminals in the thalamus and cortex in highestconcentrations in association with cortical activationthat occurs naturally during wakefulness and REM

sleep

Melatonin; is a naturally occurring hormone that regulates sleepiness.Melatonin can decrease sleep latency (time between laying down andonset of sleep)

Compounds affecting NREM & REM sleep

sleep physiology - dr.ebtehag

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