[NEURO]LEC_201_RETICULAR-SYSTEM.pdf

(001) RETICULAR FORMATION DR. STEVE S. ARELLANO | 12/02/2020 OUTLINE FUNCTIONS:...

(001) RETICULAR FORMATION DR. STEVE S. ARELLANO | 12/02/2020 OUTLINE FUNCTIONS: 1. Control of skeletal muscle – through the reticulospinal and I. THE RETICULAR FORMATION reticulobulbar tracts A. Median raphe nuclear group 2. Control of facial expression muscles - important in B. Paramedian reticular nuclear group controlling the muscles of C. Medial reticular nuclear group facial expression when associated with emotion. D. Lateral reticular nuclear group 3. Control of somatic and visceral sensations - By virtue of its II. CONNECTIONS central location in the cerebrospinal axis, the reticular A. Raphe Nuclei (Medulla oblongata) formation can influence all ascending pathways that pass to B. Raphe Nuclei (Rostral pons & Midbrain) supraspinal levels. C. Medial Group Connections 4. May be facilitative or inhibitory D. Paramedian Group 5. Control of the ANS E. Lateral Group 6. Control of the endocrine system - Either directly or indirectly III. OTHER CONNECTIONS through the hypothalamic nuclei A. Expiratory Center 7. Influence on biologic clocks - By means of its multiple B. Locomotor Center afferent and efferent pathways to the hypothalamus C. Respiratory Center 8. Reticular activating system D. Pneumotaxic Center E. Chemically specified systems RF NUCLEAR GROUPS A. Median raphe nuclear group B. Paramedian reticular nuclear group C. Medial reticular nuclear group I. THE RETICULAR FORMATION D. Lateral reticular nuclear group  Mass of neurons & nerve fibers extending from caudal medulla to the rostral midbrain  Continuous with the zona incerta (subthalamus), intralaminar & reticular nuclei (thalamus)  This is definite nuclear group with known afferent and efferent confections. It comprises a neural system with multiple inputs and multi synaptic system of impulse conduction.  receives input from most of the sensory systems and has efferent fibers that descend and influence nerve cells at all CNS levels Figure 2. Depicts the location of the Reticular Nuclei Groups A. MEDIAN RAPHE NUCLEAR GROUP Includes the following:  Midline Nuclei:  Raphe Obscurus (Medulla Oblongata)  Raphe Pallidus (Medulla Oblongata)  Raphe Magnus (Caudal Pons & Rostral Medulla) Figure1. The Reticular Formation  Raphe Pontis (Pons)  Dorsal Raphe (Midbrain) Early neuroscientists:  Superior Central (Bekhterev) Nuclei (Midbrain)  Reticulated appearance of the core formed by a non- patterned mixture of neurons & myelinated fibers  Superior Vestibular Nucleus  Non-specific system  Neurotransmitter : Serotonin 50’s & 60’s Ascending Reticular Activating System (ARAS)  Role in wakeful & alert states  Term ‘brain stem reticular core’ remains in common use Page 1 of 7 PREPARED BY: CMED 1B  (001) RETICULAR FORMATION DR. STEVE S. ARELLANO | 12/02/2020 Figure 3. The midbran showing the RN groups B. PARAMEDIAN RETICULAR NUCLEAR GROUP Figure 5. Midbrain showing location of the Medial Reticular Nuclear group  Located lateral to the medial longitudinal fasciculus (MLF) & the medial lemniscus (ML)  Includes: D.LATERAL RETICULAR NUCLEAR GROUP o Paramedian reticular nucleus (rostral medulla & caudal Includes: pons)  Nucleus Reticularis Parvocellularis (Medulla o Reticulotegmental nucleus (rostral pons & caudal Oblongata) midbrain)  Nucleus Reticularis Lateralis (Medulla Oblongata)  Nucleus Reticularis Parvocellularis (Pons)  Parabrachial Nuclei (Rostral Pons & Caudal Midbrain)  Pedunculopontine Nuclei (Rostral Pons & Caudal Midbrain)  Cuneiform Nuclei (Midbrain)  Subcuneiform Reticular Nuclei (Midbrain)  Reticular Nuclei II. CONNECTIONS A. RAPHE NUCLEI (MEDULLA OBLONGATA) Inputs from:  Spinal cord  Trigeminal sensory nuclei (2nd order)  Preaqueductal gray matter (midbrain) Project to: Figure 4. Midbrain showing location of the Paramedian Nuclear  Cerebellum Group  Dorsal horn of SC (spinothalamic neurons) C. MEDIAL RETICULAR NUCLEAR GROUP  Trigeminal nuclei Includes: B.RAPHE NUCLEI (RESTRAK PONS & MIDBRAIN)  Nucleus Reticulars Gigantocellularis (Medulla Inputs from: Oblongata)  Prefrontal cortex  Reticularis Pontis Caudalis (Pons)  Limbic system  Nucleus Reticularis Pontis Oralis (Pons)  Hypothalamus Project to:  Forebrain  Cerebellum  Brain stem ***Note: - Caudal raphe nuclei are involved in pain mechanisms – - Rostral raphe nuclei are part of the reticular activating system (RAS) concerned with wakefulness, alertness, & sleep. Page 2 of 7 PREPARED BY: CMED 1B  (001) RETICULAR FORMATION DR. STEVE S. ARELLANO | 12/02/2020 C.MEDIAL GROUP CONNECTIONS Inputs from: E. LATERAL GROUP  Spinal cord (spinoreticular) Inputs from Contralateral red nucleus  Collaterals from o Spinal Cord (spinotahalamic & spinoreticular tracts) o Ascending sensory systems o 2nd order neurons of the trigeminal, auditory, & o Superior colliculus (tectoreticular) vestibular sensory systems o Cerebellum (vestibulocerebellum) Project to o Hypothalamus o Cerebellar hemispheres o Cerebral cortex o Medial group of reticular nuclei Descending projections to:  Spinal cord (pontine &medullary reticulospinal tracts) III. OTHER CONNECTIONS Descending projections to:  Intralaminar nuclei (thalamus)  Basal cholinergic nuclei A. EXPIRATORY CENTER o Nucleus basalis of Meynert o Nucleus of the diagonal band  Location: parvocellular reticular area  Walking movements B. LOCOMOTOR CENTER  Pedunculopontine nucleus (rostral pons-caudal midbrain)  Inputs from: a. Cerebral cortex b. Medial segment of GP c. SNpr  Projects to: a. Thalamus b. SNpc C. RESPIRATORY CENTER Major brain centers that affect RESPIRATION: 1. Medulla oblongata  Stimulated by increased CO2 concentration & by decreases O2 levels in arterial blood  includes Ventral respiratory group (VRG) & Dorsal respiratory group (DRG) 2. Pons  Includes Pontine respiratory group (PRG): Apneustic center & Pneumotaxic center  Apneustic center or APC o Increases the depth & duration of inspiration o Sends signals for inspiration for long & deep breaths o Controls the intensity of breathing o Inhibited by: a. Stretch receptors of the pulmonary muscles b. Pneumotaxic center - Increases tidal volume Figure 6. Artist rendition of the brain showing the Nucleus Basalis of Meynert Apneustic breathing  Caused by damage to the pons or upper medulla by **Note: strokes or trauma Descending projections has a role in motor control  Ominous sign with a generally poor prognosis Ascending projections relate to consciousness & alertness Nucleus Reticularis Pontis Caudalis is associated with D. PNEUMOTAXIC CENTER (PNC) Paradoxical sleep  Location: dorsal part of upper third of Pons Varolii D. PARAMEDIAN GROUP  Role: Regulation of neuronal activity from sources inhibiting dorsal respiratory group (DRG) - Inputs from  Action: Sets duration of inspiration for every respiratory cycle  Spinal cord (spinoreticular)  Decreases depth and duration of inspiration  Cerebral cortex  Vestibular nuclei - Project to the cerebellum - Designated as Pre-Cerebellar nuclei Page 3 of 7 PREPARED BY: CMED 1B  (001) RETICULAR FORMATION DR. STEVE S. ARELLANO | 12/02/2020 Connections 1. Reticular Nucleus of Thalamus  Continuation of the RF of the brain stem into the diencephalon  Inputs from: a. Cerebral cortex b. Other thalamic nuclei  Projects to: a. Other thalamic nuclei o NT: GABA o Role: Integrating & Gating Activities Of Thalamic Nuclei E. CHEMICALLY SPECIFIED SYSTEMS A. Cholinergic System Figure 8. Illustration of Nucleus Basalis of Meynert 1. Cholinergic neurons: a. Rostral Pons-Caudal Midbrain B. Monoaminergic System b. Basal Forebrain Four types of neurons: 2. Pedunculopontine reticular nucleus (PRN) 1. Dopaminergic (DA) - Location: tegmentum (body) of the Pontomesencephalic 2. Noradrenergic (NA) Junction 3. Adrenergic - Roles: Arousal & Movement 4. Serotonergic - Belong to Locomotor Center - Neurons Are Affected in Patients With Progressive DOPAMINERGIC NEURONS Supranuclear Palsy Or Psp (Degenerative CNS Disease) - Location: VTA of midbrain (Ventral tegmental area of Tsai) & SNpc - 3 pathways:  Mesostriatal (Nigrostriatal)  Receives inputs from SN to striatum (caudate and putamen)  Interruption is associated with Parkinson’s Disease (PD)  Mesolimbic  Receives Inputs from Ventral Tegmental Area to Limbic Nuclei  Overactivity Will Result to Schizophrenic Hallucinations  Mesocortical  Receives Inputs from Ventral Tegmental Area to Prefrontal Cortex  Lesions: Cognitive Deficits In PD NORADRENERGIC NEURONS 2 major components 1. Norepinephrine (Ne) System Of The Locus Ceruleus  Catecholamine neuron cell group A6 Figure 7. PSP patient 2. Lateral tegmental NE system  Location: Pons and Medulla (Groups A1 to A7) PROGRESSIVE SUPRANUCLEAR PALSY/ STEELE-  Projects to SC, brain stem, cerebellum, diencephalon, and RICHARDSON-OLSZEWSKI SYNDROME telencephalon  Role: modulation of attention, sleep-wake state & mood Features: o Affects elderly Noradrenergic enhancing drugs o Pseudobulbar palsy - Treatment for: o Initially involves downgaze  Attention Deficit Disorder (ADD) o Subsequent defective up and horizontal gaze  Sleep Disorder (ex.: Narcolepsy) o Gait ataxia o Dementia 3. Nucleus basalis of Meynert - Location: Basal Forebrain - Sends Axons to Almost the Entire Cerebral Cortex - Neurons Associated with Memory Decline in Ad Page 4 of 7 PREPARED BY: CMED 1B  (001) RETICULAR FORMATION DR. STEVE S. ARELLANO | 12/02/2020 -Mediated via: Reticular connections to motor neurons of the SC & CN nuclei - Triggered by: Activities in the cerebral cortex & cerebellum In general:  Pontine Reticular Formation (PRF) exerts facilitatory influences  Medullary reticular formation (MRF) exerts inhibitory influences Somatic Motor Function  Paramedian Pontine Reticular Formation (PPRF) o Integrates horizontal eye movements via ipsilateral CN VI nucleus (abduscens nerve) to synapse with Medial Longitudinal Fasciculus (MLF) then cross to the Contralateral Medial Rectus (MR) Subnucleus Of The Oculomotor Nucleus  Conjugate gaze o Ability of eyes to work together/ in unison refers to the Figure 9. Illustration showing the Dopamine and Serotonin pathways motion of the eyes in the same direction at the same in the brain. time the eyes can look laterally, (to the left, right, upwards, downwards) governed by several nervous ADRENERGIC NEURONS system parts CN VI, MLF, Extraocular muscles (medial - Inputs from: Brain stem, Cerebellum, Spinal cord rectus, lateral rectus), interneurons command from - Role: Modulation of autonomic (symphatetic) function as in BP higher center will reach the brainstem(rostral medulla regulation and caudal pons) it is where the nuclei of abducens - Location: Caudal Medulla nerve (CN VI) is located the ipsilateral nucleus (right - Project to: Spinal Cord, Brain stem, Thalamus and Hypothalamus nuclei) will have its axon that innervate the lateral rectus of the ipsilateral eye; on the other hand the left nuclei of SEROTOGENIC NEURONS CN VI will cross via MLF to innervate the CN - Comprising nine cell groups: B1-B9 III/oculomotor nerve and synapse and innervate the - Location: raphe nuclei (midbrain, pons, & medulla) medial rectus of contralateral eye resulting to unison of - Projections: movements. a. forebrain b. cerebellum c. medulla d. SC - Role: Psychiatric Disorders (depression, OCD, aggression & anxiety) MONOAMINERGIC SYSTEM - Nucleus raphe magnus (medulla oblongata) to the SC - Inhibit dorsal horn neurons that give rise to the SPINOTHALAMIC TRACT (STT) - Serotonin (Ser) containing neurons  Role in sleep  Inhibition of Ser synthesis or destruction of Ser- containing neurons in the raphe system leads to insomnia. **Dopaminergic (DA) neurons – Have restricted area of terminal distribution **Noradrenergic (NA), Adrenergic, and Serotonergic (Ser) Figure 10. Shows the movement and mechanisms of conjugate gaze neurons – Have diffuse & widespread projection Somatic Sensory Function E. FUNCTIONS OF THE RETICULAR SYSTEM  RF exerts and effect on the transmission of sensory impulses which is triggered by cortical activity Functions of the Reticular formation  Effect is both facilitatory & inhibitory 1. Somatic Motor  Exerted on sensory nuclei of the SC & brain stem, including 2. Somatic Sensory CN nuclei 3. Visceral Motor  Nucleus raphe magnus (from medulla oblongata) 4. Arousal & Sleep o Role: inhibition of pain transmission (analgesia) Page 5 of 7 PREPARED BY: CMED 1B  (001) RETICULAR FORMATION DR. STEVE S. ARELLANO | 12/02/2020 Visceral Motor Function  Reticular Nuclei of Medial group (medulla oblongata) o Stimulation elicits and inspiratory response & depressor effect on the circulatory system (decreases Heart rate (HR) & lowers BP)  Reticular Nuclei Of Lateral Group o Stimulation elicits an expiratory response & pressor effect on circulatory system (increases HR & elevates BP)  Pontine Reticular Center o Pneumotaxic center o Regulates respiratory rhythm o Location: Kolliker-Fuse nuclei, dorsal to the motor nucleus of CN V o Connected to the medullary respiratory centers AROUSAL & ALERTNESS  RF plays a role in arousal & alertness through the ascending reticular activating system (ARAS)  Ascending reticular activating system (ARAS) o Described by Morruzi (Italy) & Magoun (USA), 1940s o Multisynaptic pathway from the RF to the diencephalon, and to the cortex o Role: cortical arousal & sharpening the attentiveness of the cortex to incoming sensory stimuli o Stimulation - arousal, alertness & attentiveness o Learning is greatly enhanced during stimulation of the ARAS o Destruction – somnolence or coma o Trigeminal stimuli are particularly effective o Sectioning or cutting below the level of the trigeminal nerve (pons) retain the arousal response o Sectioning or cutting at the level of the trigeminal nerve (pons) lose the arousal response & become stuporous o Receives constant feedback from the cerebral cortex & the peripheral receptors o Feedback mechanisms help maintain the state of arousal o Depression in the state of consciousness as result of any degenerative brain disease due impart to interruption of feedback from cortex to the RF TEST YOUR KNOWLEDGE *REFER TO TRANS IN LIMBIC SYSTEM* REFERENCES Powerpoint presentation Lecture Snell’s Clinical Neuroanatomy 8th Edition Page 6 of 7 PREPARED BY: CMED 1B  (001) RETICULAR FORMATION DR. STEVE S. ARELLANO | 12/02/2020 APPENDIX Media Raphe Paramedian Medial Lateral Medulla Raphe Obscurus Reticularis Reticularis Parvocellularis Raphe Pallidus Gigantocellularis Rostral medulla & Raphe Magnus Paramedian Caudal Pons Reticular Pons Raphe Pontis Reticularis Pontis Caudalis Reticularis Parvocellularis Reticularis Pontis Oris Rostral pons & Retivulotegmental Parabrachial Caudal midbrain Pedunculopontine Midbrain Dorsal Raphe (Nucleus Cuneiform Subcuneiform Supra Trochlearis) Superior Central (Bekhterev) Table 1. Chart showing the different Reticulara Nuclei distributed in the different parts of the brainstem Page 7 of 7 PREPARED BY: CMED 1B