RETICULAR FORMATION, SLEEP RETICULAR FORMATION, SLEEP AND WAKEFULNESSAND WAKEFULNESS

PHYSIOLOGYPHYSIOLOGY

Raquel Duarte

RETICULAR FORMATIONRETICULAR 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 RETICULAR FORMATION –AFFERENT & EFFERENT CONNECTIONS OF RETICULAR FORMATIONCONNECTIONS OF RETICULAR FORMATION

Reticular Formation

Reticular Formation

Cerebellum

Red Nucleus

Thalamus, Hypothalamus

SC

CortexSubstancia Nigra

Tectum

EFFERENT CONNECTION TO EFFERENT CONNECTION TO THE RETICULAR FORMATIONTHE RETICULAR FORMATION

AFFERENT CONNECTION TO AFFERENT CONNECTION TO THE RETICULAR FORMATIONTHE RETICULAR FORMATION

Cortex

Thalamus

Corpus Striatum

Cerebellum

SC

Sensory Pathways

(Touch, pain, temperature, kinesthestic sensation)

Optic, auditory olfactory and taste pathways

FUNCTIONAL DIVISIONS FUNCTIONAL DIVISIONS OF RETICULAR OF RETICULAR

FORMATIONFORMATIONRETICULAR RETICULAR

ACTIVATION SYSTEM ACTIVATION SYSTEM (RAS)(RAS)

RETICULAR FORMATION & ITS CONNECTIONS

Name given to

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 - ASCENDING RETICULAR ACTIVATION SYSTEM - ARASARAS

• 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 DESCENDING RETICULAR ACTIVATION SYSTEM - DRASSYSTEM - DRAS

INHIBITORYINHIBITORY

• Smoothness and accuracy of voluntary movements;

• Reflex movements;

• Regulates muscle tone;

• Maintenance of posture;

• Control of vegetative functions.

FACILITATORYFACILITATORY

• Maintains the muscle tone;

• Facilitates autonomic functions;

• Activates ARAS.

RETICULAR FORMATION: FUNCTIONSRETICULAR FORMATION: FUNCTIONS

• REGULATION OF SLEEPREGULATION OF SLEEP, thus, the maintenance of the SLEEPING cycle or CIRCADIAN SLEEPING cycle or CIRCADIAN rhythmrhythm;

• Filtering of incoming stimuli to discriminate irrelevant background stimuli;

• It’s crucial to maintain the state of CONSCIOUSNESSCONSCIOUSNESS related to the circadian rhythm – MELATONIN MELATONIN effects on RASeffects on RAS;

• ANS controlANS control – respiratory rate, heart rate, GIT activity.

SLEEPSLEEP

• 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 & SLEEP & BRAIN WAVESBRAIN WAVES

“Electroencephalography (EEG) is the

measurement of electrical activity

produced by the brain (cortex) as recorded

from electrodes placed on the scalp.“

Measured by

Determined by the level of excitationlevel of excitation of different parts of the brain resulting from

sleep, wakefulness or brain diseasessleep, wakefulness or brain diseases (epilepsy and psychosis).

SLEEP : SLOW- WAVE SLEEPSLEEP : SLOW- WAVE SLEEP

• In this type of sleep the brain wavesbrain waves are very strong & very strong & show a show a low low frequencyfrequency;

• Occurs during the first hourfirst hour after going to sleep & it’s exceedingly restful;

• ↓ ↓ of peripheral vascular toneof peripheral vascular tone & other vegetative functions of the body, such as: a 10 to 30 % ↓ in BP, in respiratory rate & in basal metabolic ratea 10 to 30 % ↓ in BP, in respiratory rate & in basal metabolic rate;

• Called “dreamless sleepdreamless sleep”, although dreams do occur during this phase.

• The difference between this and REM sleep is that they’re associated with less bodily muscle activityless bodily muscle activity & also that during this phase the consolidation of dreams in memory doesn’t occurconsolidation of dreams in memory doesn’t occur.

SLEEP : SLOW- WAVE SLEEPSLEEP : SLOW- WAVE SLEEP

• More restful type of sleep;

• Associated with(viscero-)motor activities;

• 4 Phases:- I I (Drowsiness)Drowsiness): low voltage

fluctuations, alpha waves reduced;

- II II (Light sleepLight sleep): low voltage of delta waves;

- IIIIII (Medium sleepMedium sleep): frequency of delta waves reduced, amplitude increases;

- IVIV (Deep sleepDeep sleep): delta waves more prominent, low frequency and high altitude.

SLEEP : REM ( RAPID EYE MOVEMENT) SLEEP, SLEEP : REM ( RAPID EYE MOVEMENT) SLEEP, PARADOXICAL SLEEP, DESYNCHRONIZED SLEEPPARADOXICAL 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 characteristicsREM characteristics::

1.1. Active dreaming & active bodily muscle movements;Active dreaming & active bodily muscle movements;

2.2. The person is The person is moremore difficult to arouse by sensory difficult to arouse by sensory stimuli stimuli than during the than during the deep slow- wave sleep & people usually awaken spontaneously during a deep slow- wave sleep & people usually awaken spontaneously during a REM episode;REM episode;

3.3. Muscle tone is exceedingly depressed – strong inhibition of the spinal Muscle tone is exceedingly depressed – strong inhibition of the spinal muscle control areas;muscle control areas;

4.4. Heart rate & respiratory rate become irregular;Heart rate & respiratory rate become irregular;

5.5. Irregular muscle movements occur;Irregular muscle movements occur;

6.6. Brain is ↑ active & brain waves are similar to those of wakefulness.Brain is ↑ active & brain waves are similar to those of wakefulness.

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

• 5-30 min5-30 minutesutes long, every 90 long, every 90 minutesminutes;

• ↓↓ muscle tonemuscle tone;

• ↑↑ brain metabolismbrain metabolism ( as much as 20 % );

• Irregular heart and respiratory rate;

• RRapidapid eye movements eye movements;

• LLess restful, desynchronisedess restful, desynchronised;

• Associated with psychical activities, such as dreamingdreaming.

CIRCADCIRCADIIAN RHYTHMAN 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.

REGULATION OF SLEEPREGULATION OF SLEEP

CIRCADEAN RHYTHMCIRCADEAN RHYTHM

The classic phase markers for the measuring of the circadian

rhythm are

BODY BODY TEMPERATURETEMPERATURE

MELATONIN secretion by the

pineal body

• Melatonin is absent or undetectibly low during the dayabsent or undetectibly low during the day;

• Dim- Light Melatonin OnsetDim- Light Melatonin Onset ( DLMO) is at +- 9 p.m.;

• Melatonin offset & sleep offset were found to be related recentently.

• SADSAD ( Seasonal Affective Disorder)

• DSPSDSPS ( Delayed Sleep Phase Syndrome)

• Among others ( fatigue, insomnia, bipolar disorders, sleep disorderssleep disorders, …).

Disturbances to the rhythm

SLEEP DISORDERSSLEEP DISORDERS

• Insomnia;

• Hypersomnia;

• Narcolepsy and Cataplexy;

• Sleep Apnea Disorder;

• Nightmare & Night Terror;

• Somnambulism;

• Nocturnal Enuresis;

• Movement Disorders during sleep.

REGULATION OF SLEEPREGULATION 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 raphe nuclei in the lower half of the pons & in the medullathe pons & in the medulla;

• The nucleus of the tractus solitariusnucleus of the tractus solitarius;

• Several regions of the diencephalondiencephalon, such as rostral portion of the rostral portion of the hypothalamushypothalamus ( mainly in the suprachiasmal area) & an occasial area in the diffuse nuclei of the thalamusdiffuse 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 SEROTONINSEROTONIN,

that if blocked doesn’t allow the production of sleep for several

days.

REGULATION OF SLEEPREGULATION 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 INTENSE

WAKEFULNESSWAKEFULNESS

These type of lesions can lead to death of the animal due to exhaustionexhaustion.

REGULATION OF SLEEPREGULATION 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 SLEEPBASIC THEORIES OF SLEEP

• PASSIVE THEORY OF SLEEPPASSIVE 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 active inhibitory processprocess, once that there seems to be a center located below the center located below the midpontile level of the brain stem that is required to cause sleep by midpontile level of the brain stem that is required to cause sleep by inhibiting other parts of the braininhibiting other parts of the brain;

• ONTOGENONTOGENICIC HYPOTHESIS OF REM SLEEP HYPOTHESIS OF REM SLEEP says that the activity occurring during neonatal REM sleepneonatal 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 SLEEPPHYSIOLOGICAL 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 SLEEPPHYSIOLOGICAL 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 NORMAL LEVELS OF BRAIN ACTIVITY & NORMAL BALANCE AMONG THE DIFFERENT ACTIVITY & NORMAL BALANCE AMONG THE DIFFERENT FUNCTIONS OF THE CNSFUNCTIONS OF THE CNS;

“ “ The principal value of sleep is to restore the natural balances The principal value of sleep is to restore the natural balances among the neuronal centers.”among the neuronal centers.”

CYCLE BETWEEN SLEEP & WAKEFULNESSCYCLE BETWEEN SLEEP & WAKEFULNESS

• There’s yet no explanation for the reciprocal operation of the sleep-wakefulness cycle;

• But some suggest that when the sleep centers are NOT activatedsleep centers are NOT activated, the mesencephalic & upper pontile RAS are released from inhibitionmesencephalic & upper pontile RAS are released from inhibition, which , which allows the allows the RAS to become spontaneously activeRAS to become spontaneously active;

• This will excite PNS & excite PNS & CCerebral erebral CCortexortex, 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.

• 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

BIBLIOGRAPHYBIBLIOGRAPHY

Thank you for Thank you for your attention!your attention!