RETICULAR FORMATION, SLEEP AND WAKEFULNESS

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RETICULAR FORMATION, SLEEP AND WAKEFULNESS

• PHYSIOLOGY
• Raquel Duarte

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RETICULAR FORMATION

• Diffuse mass of neurons nerve fibers that make
  the core of the brain stem
• They run through the medulla oblongata, pons
  midbrain

• Nc. of medullary reticular formation
• Nc. of pontine reticular formation
• Nc. of midbrain reticular formation

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RETICULAR FORMATION AFFERENT EFFERENT
CONNECTIONS OF RETICULAR FORMATION
Optic, auditory olfactory and taste pathways
Sensory Pathways
Cerebellum
Substancia Nigra
Thalamus
Cortex
Reticular Formation
Red Nucleus
Reticular Formation
Cortex
Cerebellum
SC
SC
Tectum
(Touch, pain, temperature, kinesthestic
sensation)
Thalamus, Hypothalamus
Corpus Striatum
EFFERENT CONNECTION TO THE RETICULAR FORMATION
AFFERENT CONNECTION TO THE RETICULAR FORMATION
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FUNCTIONAL DIVISIONS OF RETICULAR FORMATION
RETICULAR ACTIVATION SYSTEM (RAS)
Name given to
RETICULAR FORMATION ITS CONNECTIONS
Its believed to be the center of arousal and
motivation in mammals (including humans).
ASCENDING RETICULAR ACTIVATION SYSTEM
DESCENDING RETICULAR ACTIVATION SYSTEM
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ASCENDING RETICULAR ACTIVATION SYSTEM - ARAS

• Receives fibers from the sensory pathways via
  long ascending spinal tracts.
• Alertness, maintenance of attention and
  wakefulness.
• Emotional reactions, important in learning
  processes.
• Tumor or lession sleeping sickness or coma.

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DESCENDING RETICULAR ACTIVATION SYSTEM - DRAS

• INHIBITORY
• Smoothness and accuracy of voluntary movements
• Reflex movements
• Regulates muscle tone
• Maintenance of posture
• Control of vegetative functions.

• FACILITATORY
• Maintains the muscle tone
• Facilitates autonomic functions
• Activates ARAS.

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RETICULAR FORMATION FUNCTIONS

• REGULATION OF SLEEP, thus, the maintenance of the
  SLEEPING cycle or CIRCADIAN rhythm
• Filtering of incoming stimuli to discriminate
  irrelevant background stimuli
• Its crucial to maintain the state of
  CONSCIOUSNESS related to the circadian rhythm
  MELATONIN effects on RAS
• ANS control respiratory rate, heart rate, GIT
  activity.

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SLEEP

• Unconciousness state from which a person can be
  aroused by sensory or other stimuli
• Has multiple stages from very deep to very light
  sleep
• Its divided into two entirely different types of
  sleep that have different quantities alternate
  slow- wave sleep (NREM) rapid eye movement
  sleep ( REM).

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SLEEP BRAIN WAVES
Determined by the level of excitation of
different parts of the brain resulting from
sleep, wakefulness or brain diseases (epilepsy
and psychosis).
Measured by

• Electroencephalography (EEG) is the measurement
  of electrical activity produced by the brain
  (cortex) as recorded from electrodes placed on
  the scalp.

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SLEEP SLOW- WAVE SLEEP

• In this type of sleep the brain waves are very
  strong show a low frequency
• Occurs during the first hour after going to sleep
  its exceedingly restful
• ? of peripheral vascular tone other vegetative
  functions of the body, such as a 10 to 30 ? in
  BP, in respiratory rate in basal metabolic
  rate
• Called dreamless sleep, although dreams do
  occur during this phase.
• The difference between this and REM sleep is that
  theyre associated with less bodily muscle
  activity also that during this phase the
  consolidation of dreams in memory doesnt occur.

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SLEEP SLOW- WAVE SLEEP

• More restful type of sleep
• Associated with(viscero-)motor activities
• 4 Phases
• - I (Drowsiness) low voltage fluctuations,
  alpha waves reduced
• II (Light sleep) low voltage of delta waves
• III (Medium sleep) frequency of delta waves
  reduced, amplitude increases
• IV (Deep sleep) delta waves more prominent, low
  frequency and high altitude.

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SLEEP REM ( RAPID EYE MOVEMENT) SLEEP,
PARADOXICAL SLEEP, DESYNCHRONIZED SLEEP

• Bouts of REM sleep last for 5 to 30 min usually
  appear on average every 90 minutes
• As the person becomes more rested during the
  night, the durations of the REM bouts ?

• REM characteristics
• Active dreaming active bodily muscle movements
• The person is more difficult to arouse by sensory
  stimuli than during the deep slow- wave sleep
  people usually awaken spontaneously during a REM
  episode
• Muscle tone is exceedingly depressed strong
  inhibition of the spinal muscle control areas
• Heart rate respiratory rate become irregular
• Irregular muscle movements occur
• Brain is ? active brain waves are similar to
  those of wakefulness.

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SLEEP REM ( RAPID EYE MOVEMENT) SLEEP,
PARADOXICAL SLEEP, DESYNCHRONIZED SLEEP

• 5-30 minutes long, every 90 minutes
• ? muscle tone
• ? brain metabolism ( as much as 20 )
• Irregular heart and respiratory rate
• Rapid eye movements
• Less restful, desynchronised
• Associated with psychical activities, such as
  dreaming.

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CIRCADIAN RHYTHM
REGULATION OF SLEEP

• 24 hours cycle in BIOCHEMICAL, PHYSIOLOGICAL
  BEHAVIOURAL processes of living organisms

Also called the SLEEPING CYCLE

• The CIRCADIAN RHYTHM is differentiated from other
  coincidental or apparent cycles according to
  three general criteria
• Rhythm persists in constant conditions within a
  period of 24h (absence of external stimuli)
• Rhythm is temperature-compensated
• Rhythm can be reset by exposure to external
  stimuli.

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CIRCADEAN RHYTHM

• SAD ( Seasonal Affective Disorder)
• DSPS ( Delayed Sleep Phase Syndrome)
• Among others ( fatigue, insomnia, bipolar
  disorders, sleep disorders, ).

Disturbances to the rhythm
The classic phase markers for the measuring of
the circadian rhythm are
MELATONIN secretion by the pineal body
BODY TEMPERATURE

• Melatonin is absent or undetectibly low during
  the day
• Dim- Light Melatonin Onset ( DLMO) is at - 9
  p.m.
• Melatonin offset sleep offset were found to be
  related recentently.

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SLEEP DISORDERS

• Insomnia
• Hypersomnia
• Narcolepsy and Cataplexy
• Sleep Apnea Disorder
• Nightmare Night Terror
• Somnambulism
• Nocturnal Enuresis
• Movement Disorders during sleep.

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REGULATION OF SLEEP

• Stimulation of certain specific areas of the
  brain can produce sleep with characteristics near
  those of natural sleep, such as
• The raphe nuclei in the lower half of the pons
  in the medulla
• The nucleus of the tractus solitarius
• Several regions of the diencephalon, such as
  rostral portion of the hypothalamus ( mainly in
  the suprachiasmal area) an occasial area in the
  diffuse nuclei of the thalamus.

Which send fibers to the brain stem reticular
formation also to the hypothalamus, thalamus,
most of the areas of the limbic system, to the
neocortex also to the SC
Many nerve endings from these fibers produce
SEROTONIN, that if blocked doesnt allow the
production of sleep for several days.
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REGULATION OF SLEEP

• Lesions in the raphe nuclei lead to high state of
  wakefulness
• Bilateral lesions in the medial rostral
  suprachiasmal area in the anterior hypothalamus
  also cause wakefulness

In both cases, the excitatory reticular nuclei of
the mesencephalon and upper pons become released
from inhibition, thus causing INTENSE WAKEFULNESS
These type of lesions can lead to death of the
animal due to exhaustion.
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REGULATION OF SLEEP

• There are also other possible transmitter
  substances related to sleep

It has been shown that in the CSF, in blood or
urine of animals kept awake over a long period,
there are substances that cause sleep when
injected into the brain ventricular system of
another animal.

• MURAMYL PEPTIDE in CSF
• Another nonpeptide isolated from blood of
  sleeping animals
• Another unidentified substance found in the
  neuronal brain stem of animals, causes the
  accumulation of sleep factors ( in CSF or in the
  brain stem) leading to sleep.

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BASIC THEORIES OF SLEEP

• PASSIVE THEORY OF SLEEP this earlier theory of
  sleep said that the RAS became simply fatigued
  during the day as a result inactivated during
  the night
• It was later proved that sleep is caused by an
  active inhibitory process, once that there seems
  to be a center located below the midpontile level
  of the brain stem that is required to cause sleep
  by inhibiting other parts of the brain
• ONTOGENIC HYPOTHESIS OF REM SLEEP says that the
  activity occurring during neonatal REM sleep (or
  active sleep) seems to be particularly important
  to the developing organism. Deprivation of active
  sleep early in life was shown to result in
  behavioral problems, permanent sleep disruption,
  decreased brain mass.

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PHYSIOLOGICAL CHANGES DURING SLEEP

• Plasma volume decreases
• Heart rate decreases
• Blood pressure decreases
• Rate and force of respiration decreases
• Salivary secretion decreases
• Secretion of gastric juice does not alter or
  slightly increases
• Formation of urine decreases
• Sweat secretion increases
• Lacrimal secretion decreases
• Muscle tone and reflexes decrease except ocular
  muscles

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PHYSIOLOGICAL EFFECTS OF SLEEP

• Sleep has two major effects at the level of the
  nervous system at the level of other functional
  systems of the body
• The effects on the CNS are far more important
  prolonged wakefulness is associated with
  progressive malfunction of the thought processes
  can cause abnormal behavioural activities
• Sleep, in multiple ways, restores both NORMAL
  LEVELS OF BRAIN ACTIVITY NORMAL BALANCE AMONG
  THE DIFFERENT FUNCTIONS OF THE CNS

The principal value of sleep is to restore the
natural balances among the neuronal centers.
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CYCLE BETWEEN SLEEP WAKEFULNESS

• Theres yet no explanation for the reciprocal
  operation of the sleep-wakefulness cycle
• But some suggest that when the sleep centers are
  NOT activated, the mesencephalic upper pontile
  RAS are released from inhibition, which allows
  the RAS to become spontaneously active
• This will excite PNS Cerebral Cortex, both of
  which send POSITIVE FEEDBACK to the same
  reticular activating nuclei to activate them
  still further
• So, once wakefulness starts it has a natural
  tendency to sustain itself
• After a few hours, the brain even neurons
  themselves become fatigued the positive
  feedback fades sleep- promoting centers take
  over.

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BIBLIOGRAPHY

• Medical Physiology, 11th Edition, Guyton Hall
• Physiology at a Glance, Ward, Clarke Linden
• http//en.wikipedia.org/wiki/Reticular_activating_
  system
• http//en.wikipedia.org/wiki/Circadian_rhythm
• http//en.wikipedia.org/wiki/Reticular_formation

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Thank you for your attention!