Neuroscience 1A LC8 Reticular Formation PDF

[NEUROSCIENCE1A] 1.8 RETICULAR FORMATION – Dr. Steve Arellano UNIVERSITY OF NORTHERN PHILIPPINES NEUROSCIENCE 1A LC8 COLLEGE OF MEDICINE, BATCH 2026 RETICULAR FORMAT...

[NEUROSCIENCE1A] 1.8 RETICULAR FORMATION – Dr. Steve Arellano UNIVERSITY OF NORTHERN PHILIPPINES NEUROSCIENCE 1A LC8 COLLEGE OF MEDICINE, BATCH 2026 RETICULAR FORMATION: The Structure and Functions of Reticular Formation Transcribers: Quilana, Reyes, Rodriguez, Editors: Rivera, Rosalin Dr. Steve Arellano | Nov. 2022 OUTLINE I. RETICULAR FORMATION II. ORGANIZATION OF THE RETICULAR FORMATION A. Median Raphe nuclear group B. Paramedian Reticular Nuclear group C. Median reticular nuclear group D. Lateral reticular nuclear group III. GROUP CONNECTIONS IV. RESPIRATORY CENTERS V. CHEMICALLY SPECIFIED SYSTEMS VI.FUNCTIONS OF RETICULAR FORMATION VII. TEST YOUR KNOWLEDGE I. RETICULAR FORMATION Figure 2: The Median, Medial and Lateral Columns ofthe reticular Formation in the Brainstem AFFERENT AND EFFERENT PROJECTIONS Afferent Projections Figure 1: Ascending reticular formation - mass of neurons and nerve fibers extending from caudal medulla to the rostral midbrain Figure 3: Diagram showing the afferent fibers of - continuous with the zona incerta (subthalamus), intralaminar and the reticular formation reticular nuclei (thalamus) - makes person awake and aware - Projections from spinal cord: spinoreticular, - very unique part of nervous system spinothalamic, and medial lemniscus tract - present everywhere in the brain until the basal part of the - Ascending afferent tracts projecting from cranial cerebrum nerve nuclei: vestibular, acoustic, visual pathways - receives input from most of the sensory systems and has efferent - Projection from cerebellum: cerebelloreticular fibers that descend and influence nerve cells at all CNSlevels pathway - median column: intermediate size neurons - Other sources of afferent tracts: - medial column: contains large neurons o subthalamic, hypothalamic, thalamic nuclei - lateral column: contains mainly small neurons o corpus striatum - inferiorly: continuous with the interneurons of the gray matter of o limbic system the spinal cord - Afferent fibers: from primary motor cortex (frontal - superiorly: impulses are relayed to the cerebral cortex lobe), and somesthetic cortex (parietal lobe) Page 1 of 9 [NEUROSCIENCE1A] 1.8 RETICULAR FORMATION – Dr. Steve Arellano Efferent Projections - Reticulobulbar and reticulospinal tracts motor nucleiof cranial nerves and anterior horn cells of spinal cord - Sympathetic and craniosacral parasympathetic outflowof the autonomic nervous system - additional pathways extend to the corpus striatum, cerebellum, red nucleus, substantia nigra, tectum and nuclei of thalamus, subthalamus and hypothalamus HISTORY: – Early neuroscientists: reticulated appearance of the core formed by a non- patterned mixture of neurons and myelinated fibers. It is a non-specific system – 50’s and 80’s: the Ascending Reticular Activating System (ARAS) has a role in wakeful and alert states. The term “brain stem reticular core” remains in common use – Ascending Reticular Activating System (ARAS) has role in the awake. Figure 5: Group of Reticular Nuclei A. MEDIAN RAPHE NUCLEAR GROUP Includes the following: Midline nuclei: 1. Raphe Obscurus (medulla oblongata) 2. Raphe Pallidus (medulla oblongata) 3. Raphe Magnus (caudal pons and rostral medulla) 4. Raphe Pontis (pons) 5. Dorsal Raphe (midbrain) 6. Superior Central (Bekhtrev) Nuclei (Midbrain) -superior vestibular nucleus Neurotransmitter: Serotonin Figure 4: Reticular Formation According To History II. ORGANIZATION OF THE RETICULAR FORMATION RETICULAR FORMATION GROUPS: A. MEDIAN RAPHE NUCLEAR GROUP B. PARAMEDIAN RETICULAR NUCLEAR GROUP C. MEDIAL RETICULAR NUCLEAR GROUP D. LATERAL RETICULAR NUCLEAR GROUP Figure 4: Median Raphe Nuclear Group Page 2 of 9 [NEUROSCIENCE1A] 1.8 RETICULAR FORMATION – Dr. Steve Arellano B. PARAMEDIAN RETICULAR NUCLEAR GROUP D. LATERAL RETICULAR NUCLEAR GROUP Includes: Located lateral to the medial longitudinal fasciculus(MLF) & 1. Nucleus Reticularis Parvocellularis (medulla oblongata) the medial lemniscus (ML) -Nucleus reticularis parvocellularis present in both Includes: medulla and pons 7. Paramedian Reticular Nucleus (rostral medulla& caudal 2. Nucleus Reticularis Lateralis (medulla oblongata) pons) 3. Nucleus Reticularis Parvocellularis (pons) 8. Reticulotegmental Nucleus (rostral pons &caudal 4. Parabrachial Nuclei (rostral pons and caudalmidbrain) midbrain) 5. Pedunculopontine Nuclei (rostral pons and caudalmidbrain) 6. Cuneiform (midbrain) 7. Subcuneiform Reticular Nuclei (midbrain) -lots of nucleus present here in the lateral reticular nuclear group Figure 5: Paramedian Reticular Nuclear Group C. MEDIAL RETICULAR NUCLEAR GROUP Includes: 1. Nucleus Reticularis Gigantocellularis (medulla oblongata) 2. Reticularis Pontis Caudalis (pons) 3. Reticularis Pontis Oralis (pons) 4. Figure 7: Lateral Reticular Nuclear Group I III. GROUP CONNECTIONS I I A. MEDIAN GROUP CONNECTIONS. i. Raphe Nuclei (Medulla Oblongata) Inputs from: G A. Spinal cord (SC) R B. Trigeminal sensory nuclei (2nd order) O C. Periaqueductal gray matter (midbrain) U Project to: P A. Cerebellum B. Dorsal horn of spinal cord (spinothalamic neurons) C C. Trigeminal nuclei O N N Figure 6:EMedial Reticular Nuclear Group C T I Page 3 of 9 O N S [NEUROSCIENCE1A] 1.8 RETICULAR FORMATION – Dr. Steve Arellano Raphe Nuclei (Rostral Pons & Midbrain) Inputs from: A. Prefrontal cortex B. Limbic system C. Hypothalamus Project to: A. Forebrain B. Cerebellum C. Brain stem Note: Caudal raphe nuclei are involved in pan mechanisms Rostral raphe nuclei are part of the reticular activating system (RAS) concerned with wakefulness,alertness & sleep Raphe nuclei projections are very wide Figure10 : Nucleus basalis of Meynert (encircled) Difficulty in breathing and pain will lead us to awake C. PARAMEDIAN GROUP CONNECTIONS B. MEDIAL GROUP CONNECTIONS Inputs from: Inputs from: A. Spinal cord (spinoreticular) A. Spinal cord (Spinoreticular) B. Cerebral Cortex B. Collaterals from: C. Vestibular nuclei - ascending sensory systems (STT) Project to: - superior colliculus (tectoreticular) A. Cerebellum - cerebellum(vestibulocerebellum) designated as pre-cerebellar nuclei - hypothalamus - cerebral cortex D. LATERAL GROUP CONNECTIONS Descending projections to: Inputs from: A. Spinal Cord (pontine & medullary reticulospinal tracts) A. Contralateral red nucleus Ascending projections to: B. Spinal cord (Spinothalmic tract and SRT) A. Intralaminar Nuclei (Thalamus) C. 2nd order neurons of trigeminal, auditory & vestibular B. Basal Cholinergic Nuclei sensory systems - nuclei basalis of Meynert Project to: - nucleus of the diagonal band A. Cerebellar Hemispheres Note: B. Medial Group Of Reticular Nuclei Descending projections has a role in motor control Ascending projections relate to consciousness and alertness. OTHER CONNECTIONS Reticularis pontis caudalis is asscociated with paradoxical sleep Expiratory Center - location: parvocellular reticular area (medulla) Locomotor Center - walking movements - pedunculopontine nucleus (rostral pons-caudal midbrain) - Input from: A. Cerebral cortex SUPERIOR COLLICULI B. Medial segment of GP C. Substantia Nigra pars reticulata (SNpr) - Projects to: A. Thalamus B. SNpc - (Substantia Nigra pars compacta) Figure 9: Superior & Inferior Colliculi ofMidbrain (Backview) Page 4 of 9 [NEUROSCIENCE1A] 1.8 RETICULAR FORMATION – Dr. Steve Arellano IV. RESPIRATORY CENTERS RETICULAR NUCLEUS OF THALAMUS (other nuclear groups ofreticular information) Major brain centers that affect RESPIRATION: - Continuation of the RF of the brain stem into the diencephalon 1. MEDULLA OBLONGATA - Inputs from: - includes the dorsal respiratory group (DRG) and a. Cerebral cortex the ventral respiratory group (VRG) b. Other thalamic nuclei - stimulated by increase in CO2 concentration and - Projects to: decrease in O2 levels in the arterial blood a. Other thalamic nuclei - Neurotransmitter: GABA-Gamma Amino Butyric Acid - Role: Integrating and Gating activities of thalamic nuclei V. CHEMICALLY SPECIFIED SYSTEMS A. CHOLINERGIC SYSTEM B. MONOAMINERGIC SYSTEM 1. Dopaminergic (DA) 2. Noradrenergic (NA) 3. Adrenergic (A) 4. Serotonergic (Ser) A. CHOLINERGIC SYSTEM Cholinergic neurons: 1. Rostral pons-caudal midbrain 2. Basal forebrain Pedunculopontine Reticular Nucleus (PRN) - Location: tegmentum of the Figure 11: Respiratory centers (VRG and DRG) pontomesencephalic junction - Roles: arousal and movement - Belong to locomotor center 2. PONS - Neurons are affected in patients with Apneustic center or APC (pons) Progressive supranuclear palsy (PSP) - Increase the depth and duration of inspiration (degenerative CNS disease) - Enables us to sigh - Sends signal for inspiration for long and deepbreaths -Control the intensity of breathing -Increases tidal volume -Inhibited by: a. Stretch receptors of the pulmonarymuscles (peripheral) b. Pneumotaxic center *APNEUSTIC BREATHING - Caused by damage to the pons or uppermedulla, by strokes or trauma Pneumotaxic Centre or PNC - Location: dorsal part of upper third of pons Varolii - Role: regulation of neuronal activity from sources ininhibiting Dorsal Respiratory Group (DRG) Figure 13: Nucleus Basalis of Meynert - Action: sets duration of inspiration for everyrespiratory cycle - Decreases depth and duration of inspiration Page 5 of 9 [NEUROSCIENCE1A] 1.8 RETICULAR FORMATION – Dr. Steve Arellano Progressive Supranuclear Palsy (Steele-Richardson- 1. NORADRENERGIC NEURONS (NA) Olszowski Syndrome) 2 major components: a. Norepinephrine (NE) system of the locus ceruleus - catercholamine neuron cell froup A6 b. Lateral tegmental NE systems - Location: pons and medulla (groups A1 to A7) - Projects to SC, brain stem, cerebellum, diencephalon, and telencephalon - Role: modulation of attention, sleep-wake state and mood Noradrenergic enhancing drugs - Treatment for: a. Attention deficit disorder (ADD) b. Sleep Disorder (ex. Narcolepsy) 2. ADRENERGIC NEURONS (A) - Inputs from: a. Brainstem b. Cerebellum c. Spinal Cord (SC) - Role: modulation of autonomic (sympathetic) function as in BP regulation Figure 12: Signs of PSP Patient - Location: caudal medulla - Project to: a. SC Nucleus basalis of Meynert (nbM) b. Brainstem - Location: Basal Forebrain c. Thalamus and hypothalamus - Sends axons to almost the entire cerebral cortex - Neurons associated with memory decline in 3. SEROTONERGIC NEURONS (SER) Alzheimer’s Disease (AD) - Comprising nine cell groups: B1 to B9 - Location: raphe nuclei (midbrain, pons and B. MONOAMINERGIC SYSTEM medulla) Four types of neurons: - Projections: a. Forebrain 1. DOPAMINERGIC (DA) b. Cerebellum - Location: Ventral Tegmental area of midbrain (VTA of Tsai) and SNpc (Substancia Nigra pars c. Medulla compacta) d. SC (Spinal Cord) 3 Pathways: - Role: Psychiatric DSO (depression, Obsessive a. Mesotriatal (nigrostriatal) Compulsive Syndrome (OCS), aggression, and - From SN to striatum (caudate and putamen)- anxiety) pertains to basal ganglia - SSRI (prescribed): Escitalopram (cause an - Interruption is associated with PD orParkinsons increase in 5-HT levels in neuronal synapses by Disease preventing the re-uptake of 5-HT into the presynaptic terminals of serotonergic neurons) b. Mesolimbic Monoaminergic System - From VTA to limbic nuclei Nucleus Raphe Magnus (medulla oblongata) to the - Overactivity will lead to schizophrenichallucinations Spinal Cord c. Mesocortical - Inhibit dorsal horn neurons that give rise to the STT - From VTA to prefrontal cortex (Spinothalamic Tract) - Lesions: cognitive deficits in PD Serotonin (Ser) containing neurons (noradrenergic neurons) - Role in sleep - Inhibition of Ser synthesis or destruction of Ser- containing neurons in the raphe system leads to insomnia. Page 6 of 9 [NEUROSCIENCE1A] 1.8 RETICULAR FORMATION – Dr. Steve Arellano Dopaminergic (DA) neurons innervates the lateral rectus muscle of the eye. Eyeball ofthe - Have restricted area of terminal distribution left is towards the right and the eyeball of the right Noradrenergic (NA), Adrenergic, and Serotonergic (Ser) towards the right producing conjugate gaze movement neurons - Have diffuse and wide- spread projection Figure 15: Shows The Movement And Mechanisms Of ConjugateGaze Figure 14: Dopamine And Serotonin Pathways In The Brain 2. SOMATIC SENSORY FUNCTIONS RF exerts an effect on the transmission of sensory impulses which is triggered by cortical activity VI. FUNCTIONS OF RETICULAR FORMATION effect is both facilitatory and inhibitory exerted on sensory nuclei of the SC and brainstem, 1. SOMATIC MOTOR including CN nuclei 2. SOMATIC SENSORY Nucleus Raphe Magnus (medulla oblongata) 3. VISCERAL MOTOR Role: inhibition of pain transmission (analgesia) 4. AROUSAL AND SLEEP 3. VISCERAL MOTOR FUNCTION - Mediated via: reticular connections to motor neurons of the SCand Reticular Nuclei of Medial group (medulla oblongata) CN nuclei - Stimulation elicits and inspiratory response & - Triggered by: activities in the cerebral cortex and cerebellum depressor effect on the circulatory system (decreases HR - In general: & lowers BP) Pontine Reticular Formation (PRF) Reticular Nuclei of Lateral Group - Exerts facilitatory influences - Stimulation elicits an expiratory response & pressor Medullary Reticular Formation (MRF) effect on circulatory system (increases HR & elevates - Exerts inhibitory influences BP) Pontine Reticular Center 1. SOMATIC MOTOR FUNCTIONS - Pneumotaxic center Paramedian Pontine Reticular Formation (PPRF) - Regulates respiratory rhythm - Integrated horizontal eye movements from the cortex - Location: Kolliker-Fuse nuclei, dorsal to the motor (brodmann area 8 or the frontal eyefield, descend to nucleus of CN V midbrain) - Connected to the medullary respiratory centers - Via: ipsilateral CN VI nucleus to medial longitudinal fasciculus (MLF) to contralateral medial rectus (MR) 4. AROUSAL AND ALERTNESS subnucleus of the oculomotor nucleus - RF plays a role in arousal & alertness through the - ascending reticular activating system (ARAS) or in unison. It refers to the motion of both eyes in - sleep sound and wake-up strong the same direction at the same time. The eyes can look Ascending reticular activating system (ARAS) laterally (left/right), upward, or downward. The left nuclei - for regulating wakefulness and sleep-wake of CN VI will decussate to the other side via MLF and transitions synapse to CN III to innervate the medial rectus muscle of the eye; Ipsilateral nucleus in the right side Page 7 of 9 [NEUROSCIENCE1A] 1.8 RETICULAR FORMATION – Dr. Steve Arellano - described by Morruzi (Italy) & Magoun (USA),1940s- through experiment by cutting the brainstem of the cat therefore, wakefulness isinhibited; became the basis of many sleeping drugs - Multisynaptic pathway from the RF to thediencephalon, and to the cortex - Role: cortical arousal & sharpening the attentiveness of the cortex to incoming sensorystimuli - Awake first before awareness - Stimulation - arousal, alertness & attentiveness - Learning is greatly enhanced during stimulationof the ARAS - Destruction – somnolence or coma o Trigeminal stimuli are particularly effective - Sectioning or cutting below the level of the trigeminal nerve (pons) retain the arousal response - Sectioning or cutting at the level of the trigeminal nerve (pons) lose the arousal response & become stuporous - Receives constant feedback from the cerebral cortex & the peripheral receptors Feedback mechanisms help maintain the state of arousal, awake, and alive. - Depression in the state of consciousness as result of any degenerative brain disease due impart to interruption - Trigeminal is specified because it involve in sensation as well as stimulation of other sensory input from cortex that keep you awake to be able to learn and memorize RETICULAR MEDIAN RAPHE PARAMEDIAN RETICULAR MEDIAL RETICULAR NUCLEAR LATERAL RETICULAR FORMATION NUCLEAR GROUP NUCLEAR GROUP GROUP NUCLEAR GROUP NUCLEI ⚫ Nucleus Reticularis MEDULLA ⚫ Raphe obscurus Nucleus Reticularis Parvocellularis OBLONGATA ⚫ Raphe pallidus Gigantocellularis ⚫ Nucleus Reticularis Lateralis ROSTRAL MEDULLA AND Raphe magnus Paramedian reticular CAUDAL PONS ⚫ Reticularis pontis PONS Raphe pontis Nucleus Reticularis cellularis Parvocellularis ⚫ Reticularis pontis oralis ROSTRAL PONS ⚫ Parabrachial nuclei AND CAUDAL Reticulotegmental ⚫ Pedunculopontine MIDBRAIN nuclei ⚫ Dorsal Raphe ⚫ Superior Central ⚫ Cuneiform MIDBRAIN ⚫ Subcuneiform reticular (Bekhtrev) nuclei nuclei Page 8 of 9 [NEUROSCIENCE1A] 1.8 RETICULAR FORMATION – Dr. Steve Arellano VII. TEST YOUR KNOWLEDGE PRACTICE QUESTIONS: 8.The lateral group connections receive their input from 1. The following statements concern the functions of the a. Contralateral brown nucleus reticular formation: b. Spinal Cord (Spinothalamic tract and SERT) a. It influences the activity of the alpha and gamma motor c. Second-order neurons of trigeminal, auditory, & neurons. vestibular sensory systems b. It opposes the actions of the vestibular spinal tract. d. All of the above c. It does not bring about reciprocal inhibition during 9. The expiratory center is located in the contraction of the prime mover muscles. a. Parvocellular reticular area d. It plays no part in maintaining the tone of the b. Cerebral cortex antigravity muscles. c. Substantia Nigra pars reticulata e. It cannot modulate reflex activity d. Substantia Nigra pars compacta 2. The following include to median raphe nuclear group EXCEPT 10. the following are laters of the dentate gyrus, except a. Raphe pons(pons) a. molecular layer b. Dorsal aphe(midbrain) b. polymorphic later c. Superior central (Bekhtrev) Nuclei c. granule cell layer d. Cuneifrom(midbrain) d. pyramidal cell layer e. NOTA 3. Raphe nuclei coming from medulla oblongata includes the following input a. SC, Periaqueductal gray matter, Prefrontal cortex b. SC, Brainstem, Cerebellum c. Trigeminal sensory nuclei (2nd order), SC & Periaqueductal gray matter d. Periaqueductal gray matter,Limbic system & Hypothalamus 4. Reticular formation plays a role in arousal and alertness. What unit is responsible for wakefulness and sleep-wake transition? a. Paramedian Pontine Reticular Formation b. Ascending Reticular Activating System c. Medullary Reticular Formation d. Pontine Reticular Formation 5. All of the following are the functions of reticular formation except: a. Somatic Motor b. Somatic Sensory c. Visceral Motor d. Sensory Motor 6. Neurons associated with memory decline in Alzheimer’s Disease (AD) a. Nucleus basalis of Meynert (nbM) b. Mesolimbic c. Adrenergic Neurons Answers: d. Serotonergic neurons 1. A 6. A 2. D 7. B 7.Nucleus Reticularis Parvocellularis of the reticular formation are 3. C 8. C found in the ___. 4. B 9. A a. midbrain 5. D 10. D b. pons c. medulla d. None of the answers are correct (1. a, 2. b) Page 9 of 9