Transcript Reticular formation,sleep and wakefulness

RETICULAR FORMATION, SLEEP
AND WAKEFULNESS
PHYSIOLOGY
Raquel Duarte
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;
RETICULAR FORMATION –AFFERENT & EFFERENT
CONNECTIONS OF RETICULAR FORMATION
Sensory
Pathways
Cerebellum
Substancia Nigra
Cortex
Reticular
Formation
Red
Nucleus
Optic, auditory
olfactory and
taste
pathways
Thalamus
Cerebellum
Reticular
Formation
Cortex
SC
SC
Tectum
Thalamus,
Hypothalamus
EFFERENT CONNECTION TO
THE RETICULAR FORMATION
Corpus
Striatum
(Touch, pain,
temperature,
kinesthestic
sensation)
AFFERENT CONNECTION TO
THE RETICULAR FORMATION
FUNCTIONAL DIVISIONS
OF RETICULAR
RETICULAR
FORMATION
ACTIVATION SYSTEM
(RAS)
Name
given to
RETICULAR FORMATION & ITS CONNECTIONS
It’s believed to be the center of
arousal and motivation in
mammals (including humans).
ASCENDING RETICULAR
ACTIVATION SYSTEM
DESCENDING RETICULAR
ACTIVATION SYSTEM
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.
DESCENDING RETICULAR ACTIVATION
SYSTEM - DRAS
INHIBITORY
FACILITATORY
• Smoothness and accuracy of
voluntary movements;
• Maintains the muscle tone;
• Reflex movements;
• Facilitates autonomic
functions;
• Regulates muscle tone;
• Activates ARAS.
• Maintenance of posture;
• Control of vegetative functions.
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;
•
It’s crucial to maintain the state of
CONSCIOUSNESS related to the
circadian rhythm – MELATONIN
effects on RAS;
•
ANS control – respiratory rate,
heart rate, GIT activity.
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;
• It’s divided into two entirely
different types of sleep that
have different quantities &
alternate: slow- wave sleep
(NREM) & rapid eye
movement sleep ( REM).
SLEEP & BRAIN WAVES
Measured by
“Electroencephalography
(EEG) is the measurement of
electrical activity produced by
the brain (cortex) as recorded
from electrodes placed on
the scalp.“
Determined by the level of excitation of
different parts of the brain resulting from
sleep, wakefulness or brain diseases
(epilepsy and psychosis).
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 & it’s 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 they’re associated with
less bodily muscle activity & also that during this phase the
consolidation of dreams in memory doesn’t occur.
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.
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:
1. Active dreaming & active bodily muscle movements;
2. 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;
3. Muscle tone is exceedingly depressed – strong inhibition of the spinal
muscle control areas;
4. Heart rate & respiratory rate become irregular;
5. Irregular muscle movements occur;
6. Brain is ↑ active & brain waves are similar to those of wakefulness.
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.
REGULATION OF SLEEP
CIRCADIAN RHYTHM
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.
CIRCADEAN RHYTHM
Disturbances to
the rhythm
The classic phase markers for
the measuring of the circadian
rhythm are
BODY
TEMPERATURE
• SAD ( Seasonal Affective
Disorder)
• DSPS ( Delayed Sleep
Phase Syndrome)
• Among others ( fatigue,
insomnia, bipolar disorders,
sleep disorders, …).
MELATONIN
secretion by the
pineal body
• 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.
SLEEP DISORDERS
• Insomnia;
• Hypersomnia;
• Narcolepsy and Cataplexy;
• Sleep Apnea Disorder;
• Nightmare & Night Terror;
• Somnambulism;
• Nocturnal Enuresis;
• Movement Disorders during sleep.
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
doesn’t allow the production of
sleep for several days.
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.
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.
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.
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;
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.”
CYCLE BETWEEN SLEEP & WAKEFULNESS
•
There’s yet no explanation for the reciprocal operation of the sleepwakefulness 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.
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
Thank you for
your attention!