Presentation on theme: "RETICULAR FORMATION, SLEEP AND WAKEFULNESS PHYSIOLOGY Raquel Duarte."— Presentation transcript:
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 Reticular Formation Cerebellum Red Nucleus Thalamus, Hypothalamus SC Cortex Substancia Nigra Tectum EFFERENT CONNECTION TO THE RETICULAR FORMATION AFFERENT CONNECTION TO THE RETICULAR FORMATION Cortex Thalamus Corpus Striatum Cerebellum SC Sensory Pathways (Touch, pain, temperature, kinesthestic sensation) Optic, auditory olfactory and taste pathways
FUNCTIONAL DIVISIONS OF RETICULAR FORMATION RETICULAR ACTIVATION SYSTEM (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 - 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 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.
RETICULAR FORMATION: FUNCTIONS REGULATION OF SLEEP SLEEPING cycle or CIRCADIAN rhythmREGULATION OF SLEEP, thus, the maintenance of the SLEEPING cycle or CIRCADIAN rhythm; Filtering of incoming stimuli to discriminate irrelevant background stimuli; CONSCIOUSNESS MELATONIN effects on RASIt’s crucial to maintain the state of CONSCIOUSNESS related to the circadian rhythm – MELATONIN effects on RAS; ANS controlANS 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 “Electroencephalography (EEG) is the measurement of electrical activity produced by the brain (cortex) as recorded from electrodes placed on the scalp.“ Measured by level of excitation sleep, wakefulness or brain diseases 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 brain wavesvery strong & show a low frequencyIn this type of sleep the brain waves are very strong & show a low frequency; first hourOccurs during the first hour after going to sleep & it’s exceedingly restful; ↓ of peripheral vascular tone a 10 to 30 % ↓ in BP, in respiratory rate & in basal metabolic rate↓ 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; dreamless sleepCalled “dreamless sleep”, although dreams do occur during this phase. less bodily muscle activity consolidation of dreams in memory doesn’t occurThe 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) - I (Drowsiness): low voltage fluctuations, alpha waves reduced; -II Light sleep -II (Light sleep): low voltage of delta waves; -IIIMedium sleep -III (Medium sleep): frequency of delta waves reduced, amplitude increases; -IVDeep sleep -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 min utes long, every 90 minutes5-30 min utes long, every 90 minutes; ↓ muscle tone↓ muscle tone; ↑ brain metabolism↑ brain metabolism ( as much as 20 % ); I rregular heart and respiratory rate; Rapid eye movementsRapid eye movements; L ess restful, desynchronisedL ess restful, desynchronised; dreamingA ssociated with psychical activities, such as dreaming.
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. REGULATION OF SLEEP
CIRCADEAN RHYTHM The classic phase markers for the measuring of the circadian rhythm are BODY TEMPERATURE MELATONIN secretion by the pineal body absent or undetectibly low during the day Melatonin is absent or undetectibly low during the day; Dim- Light Melatonin Onset Dim- Light Melatonin Onset ( DLMO) is at +- 9 p.m.; Melatonin offset & sleep offset were found to be related recentently. SAD SAD ( Seasonal Affective Disorder) DSPS DSPS ( Delayed Sleep Phase Syndrome) sleep disorders Among others ( fatigue, insomnia, bipolar disorders, sleep disorders, …). Disturbances to the rhythm
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: raphe nuclei in the lower half of the pons & in the medullaThe raphe nuclei in the lower half of the pons & in the medulla; nucleus of the tractus solitariusThe nucleus of the tractus solitarius; diencephalon rostral portion of the hypothalamus diffuse nuclei of the thalamusSeveral 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; SEROTONIN 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; INTENSE WAKEFULNESS In both cases, the excitatory reticular nuclei of the mesencephalon and upper pons become released from inhibition, thus causing INTENSE WAKEFULNESS exhaustion 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 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; active inhibitory processcenter located below the midpontile level of the brain stem that is required to cause sleep by inhibiting other parts of the brainIt 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 neonatal REM sleepONTOGENIC 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; NORMAL LEVELS OF BRAIN ACTIVITY & NORMAL BALANCE AMONG THE DIFFERENT FUNCTIONS OF THE CNSSleep, 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 sleep- wakefulness cycle; sleep centers are NOT activated mesencephalic & upper pontile RAS are released from inhibition, which allows the RAS to become spontaneously activeBut 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; excite PNS & Cerebral CortexThis 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.
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 BIBLIOGRAPHY