Limbic System Lecture Notes PDF

(002) LIMBIC SYSTEM DR. ARELLANO | 12/04/2020 OUTLINE Two main structures: I. THE LIMBIC SYSTEM...

(002) LIMBIC SYSTEM DR. ARELLANO | 12/04/2020 OUTLINE Two main structures: I. THE LIMBIC SYSTEM A. Overview 1. Hippocampal formation B. Function II. THE LIMBIC LOBE  consolidation of short-term memory into long term memory A. Subcallosal Gyrus  receives major input via the entorhinal cortex B. Hippocampal Formation  projects major output via the fornix C. Papez Circuit D. Function of Hippocampal Formation in Memory Includes: III. AMYGDALA a. Hippocampus proper IV. BRAINSTEM CENTERS ASSOCIATED WITH LIMBIC b. Dentate gyrus SYSTEM FUCNTION c. Subiculum V. PATHWAYS OF THE LIMBIC SYSTEM 2. Amygdala  Regulates emotional expression via modulation of the hypothalamus I. THE LIMBIC SYSTEM B. FUNCTION OF THE LIMBIC SYSTEM Function of Limbic System 1. Species preservation  done by reproduction and associated instinctive behavior 2. Self-preservation  done thru feeding, behavior and aggression 3. Expression of fear, motivation, & other emotions 4. Memory 5. Learning Limbic System  Generates the emotional background for intellect  Serves to balance emotional & cognitive mechanism  Referred to as the „visceral brain‟  Has extensive connetions with hypothalamus (which integrates endocrine & ANS functions) 1. Influences Visceral responses: o Ex: increase in HR & RR, sweating, which supplement the expression of emotion Figure 1. The Limbic System II. The Limbic Lobe A. OVERVIEW The Limbic Lobe  (L. limbus, ‘border’) The Limbic System  Characterized by Paul Broca, 1878  Formed a transition border intervening between  Word limbic means “border” or “margin” and the term limbic diencephalon and the telencephalon system was loosely used to include a group of structures that lie in the border zone between the cerebral cortex and the Components: hypothalamus.  Interconnects the telencephalon, diencephalon, & brain stem Considered to be a component of the more extensive limbic  Major function: modulate the hypothalamus system a. cingulate gyrus – lesions result in akinesia, mutism, 1. Subcallosal gyrus (Neocortex) apathy, and indifference to pain 2. Cingulate gyrus (Mesocortex) b. subcallosal arca 3. Parahippocampal gyri (Neocrtex) c. parahippocampal gyrus 4. Hippocampal formation (Archicortex) d. dentate gyri e. hippocampus proper f. subiculum A. SUBCALLOSAL GYRUS g. amygdaloid body h. septal area Subcallosal Gyrus i. nuclei of the thalamus & hypothalamus  Consists of gray matter, which underlies the basal surface of the rostral part of the corpus callosum Page 1 of 8 PREPARED BY: CMED 1B  (002) LIMBIC SYSTEM DR. ARELLANO | 12/04/2020  Curves superiorly around the genu of the corpus callosum, as the cingulate gyrus B. HIPPOCAMPAL FORMATION Hippocampal Formation Component Layers Cell Bodies Dendrites Axon Terminals Hippocampus Molecular Pyramidal Granule Cells Of Proper (Deepest) Cell Dentate Gyrus Apical (Mossy Fibers) Dendrites Perforant Pathway Pyramidal Septohippocampal Cell Basal Tract *Pyramidal Dendrites *Pyramidal Cells Pyramidal Cell (Middle) *Interneurons Axon *Polymorphic Collateral (Superficial) Branches Dentate *Molecular Some Apical *Perforant Pathway Gyrus (Outer) Dendrites *Alveus Figure 2. The Hippocampal Formation. The 3-layered hippocampus *Granule Cell Granule Cells Of Granule *Collateral proper and dentate gyrus are called the Cornu Ammonis (Ammon‟s (Middle) Interneurons Cells Branches Of Horn) *Polymorphic Granule Cells  Three Regions (Deepest) 1. Hippocampus proper o Aka: hippocampus, Ammon‟s Horn, cornu ammonis Subiculum Three-Layered 2. Dentate gyrus Cortex Next To 3. Subiculum Hippocampus  Neuroanatomical connections: Six-Layered 1. Entorhinal cortex Cortex Next To 2. Supracallosal gyrus (Indusium griseum) Parahippocam 3. Fasciola cincera (Gyrus fasciolaris) pal Gyrus 4. Septal area Table 2. Components of the Hippocampal Formation  Extend from your amygdala, anteriorly to the splenium to the corpus callosum posteriorly  Consists of Archicortex  Function: recent memory and learning Cortical components of the Limbic Lobe Part of Cortex Components Allocortex Archiocortex Hippocampal formation: 1. Hippocampus proper 2. Dentate gyrus 3. Subiculum Paleocortex - Piriform cortex of the parahippocampal gyrus Juxtallocortex Mesocortex - Cingulate gyrus Isocortex Neocortex - Subcallosal gyrus - Parahippocampal gyrus Figure 3. The Hippocampal Formation showing its characteristic seahorse-like shape. Table 1. Parts of the Cortical Cortex and their components Page 2 of 8 PREPARED BY: CMED 1B  (002) LIMBIC SYSTEM DR. ARELLANO | 12/04/2020 Layers of the Hippocampal Achicortex 1. Molecular Layer  Deepest layer  Consists of nerve fibers and scattered small neurons  Located in the core of the hippocampal formation  Components: 1. Apical dendritic trees o Belong to hippocampal pyramidal cells 2. Axon terminals o Belong to granule cells whose cell bodies reside in the:  Granule cell layer (dentate gyrus)  Perforant pathway (entorhinal cortex)  Septohippocampal tract (septal area)  Pyramidal cell axon collateral branches (pyramidal cell layer of the hippocampus) 2. Pyramidal Layer Figure 4. The hippocampus at transverse section at temporal lobe.  Middle layer  Most prominent layer of the hippocampal formation HIPPOCAMPUS PROPER  Consist of pyramidal cells  Gk. Hippocampus, „seahorse‟  Dendrites ramify I the molecular layer, their axons pass in the opposite direction, across the polymorphic later, & then  Phylogenetically ancient cortical structure that forms a course in the alveus, finbria, & fornix comma-shaped prominence on the floor & medial wall of the temporal horn of the lateral ventricle **Schaffer collaterals  Ventricular surface: coated with ependymal layer  Pyramidal cell axon collateral branches  Contains pyramidal cells that project via the fornix to the septal area and the hypothalamus  Cross the polymorohic & pyramidal layers to reach the molecular layer where they form synaptic contacts with the  Coronal section: appears similar to a seahorse as a result of dendrites of other pyramidal neurons its arched form  C-chaped outline in coronal section, resembles a ram‟s horm 3. Polymorphic Layer & is called Ammon‟s horm (cornu Ammonis or CA)  Superficial layer  Infolding of human brain embedding the parahippocampal  Shares structural characteristics with the deepest layers of gyrus of temporal lobe. the neocortex  Involved in learning and memory  Lies deep to the alveus  Consists of interneurons, as well as, pyramidal cell dendrites Input sources to the Output targets of the and axon collateral branches hippocampus hippocampus Indusium griseum Septal nuclei DENTATE GYRUS Cingulate gyrus Lateral preoptic area (hypothalamus)  (L. dentate, „tooth-shaped‟) Septal nuclei Anterior part (hypothalamus)  Notched band of cortex that in interposed between the upper Entorhinal cortex Mamillary body aspect of the parahippocampal gyrus & the fimbria Dentate gyrus Anterior nuclear group  Named after its tooth-like configuration (thalamus)  has a three-layered archicortex Parahippocampal gyrus Midbrain tigmentum  contains granule cells that receive hippocampal input and Contralateral hippocampus Habenuclei project it to the pyramidal cells of the hippocampus and Table 3. Input Sources and Output targets of the Hippocampus subiculum  Dorsally it courses along the fimbria near the splenium of  Three layers of the Hippocampal Archicortex corpus callosum extend to the indusium griseum 1. molecular layer  Anteriorly it extend uncus of the parahippocampal gyrus 2. pyramidal layer 3. polymorphic layer Layers of the Dentate gyrus:  Three Zones in transverse (coronal) section: 1. Molecular Layer - Area CA1 (lies next to Subiculum)  Outer - Area CA2  Small population of nerve cell bodies & granule cell dendrites - Area CA3 (lies close to Dentate gyrus) - Area CA4 2. Granule layer  Middle  Corresponds to the pyramidal layer of the hippocampus  Cell bodies of the granule cells Page 3 of 8 PREPARED BY: CMED 1B  (002) LIMBIC SYSTEM DR. ARELLANO | 12/04/2020 1. Indusium griseum 2. Cingulate gyrus 3. Septal gyrus 4. Septal buclei 3. Polymorphic Layer 5. Entorhinal cortex  Deep layer 6. Dentate gyrus  Consists of interneurons 7. Parahippocampal gyrus 8. Contralateral hippocampus SUBICULUM  Transitional zone Efferent fibers from the hippocampus proper:  Receives input via the hippocampal pyramidal cells  Axons anterior to the anterior commissure terminate at:  Projects via the fornix to the mamillary nuclei and the anterior 1. Septal nuclei nucleus of the thalamus 2. Lateral preoptic area (hypothalamus)  Displays a three layered archicortex next to the hippocampus 3. Anterior part (hypothalamus)  Progressively becomes a more elaborate six-layered  Axons posterior to the anterior commissure: neocortex as it approaches the parahippocampal gyrus 1. Mammillary body  Receives information relayed by the hippocampal pyramidal 2. Anterior nuclear group (thalamus) cells 3. Tegmentum (midbrain)  Gives rise to fibers that join the fornix and terminate in the 4. Habenular nuclei mamillary nuclei of the hypothalamus and anterior nuclei group of the thalamus. *Hippocampo-Entorhino-Neocortical Pathway STRUCTURES ASSOCIATED WITH THE  2nd pathway  HIPPOCAMPAL FORMATION Pathway involved in the consolidation of episodic memories Intrinsic Circuit of the Hippocampal Formation A. Entorhinal Cortex (Brodmann’s area 28) Components of the hippocampal formation:  Located ventral to the amygdaloid body & anterior half of the 1. Hippocampus hippocampal formation 2. Dentate gyrus  Gives rise to the most prominent input to the dentate gyrus 3. Subiculum via: Axons from the Entorhinal cortex 1. Perforant pathway  Form the perforant (lateral) & alvear (medial) pathways o Arise from the lateral part of the entorhinal  Terminates in the molecular layer cortex  Send collaterals to the CA1 & CA3 zones 2. Alvear pathway o Arise from the medial part of the entorhinal  Provides the major input to the hippocampal formation cortex C. PAPEZ CIRCUIT B. Indusium griseum (Supracallosal gyrus)  Proposed by James Papez  Represents a portion of the hippocampal formation that  Neuroanatomical basis of emotion remained attached to the corpus callosum during its  Basis for more modern research development  A circular pathway that interconnects the major limbic  Dorsally it curves around the splenium of the corpus structures. callosum and then merge with the dentate and parahippocampal gyrus by way of Fasciola cinerea. C. Fasciola cinerea (Gyrus Fasciolaris)  (L. fasciola, “band”; cinereus, “ashen-hued”)  Transitional zone of intervening cortex that joins the dentate gyrus with the indusium griseum D. Septal area  Located in the telencephalon  Well developed in humans * Septal nuclear complex  Nuclei are gathered rostral to the anterior commissure  Two main groups: 1. Media septal nuclei 2. Lateral septal nuclei Hippocampal Proper Figure 5. The Papez Circuit flow chart Afferent fibers to the hippocampus proper arise from: Page 4 of 8 PREPARED BY: CMED 1B  (002) LIMBIC SYSTEM DR. ARELLANO | 12/04/2020 Anatomical Structures: a. Hippocampus b. Fornix c. Mammillary body d. Anterior nucleus (thalamus) e. Mammillothalamic tract f. Cingulate gyrus D. FUNCTION OF HIPPOCAMPAL FORMATION IN MEMORY Learning  Manner by which knowledge is acquired Memory  Process by which knowledge is stored and is retrievable in the future Figure 6. View of brain showing the location of the Amygdala Classification of Memory: 1. Immediate Memory Divisions  Where newly learned information is initially stored (seconds) 1. Basolateral (VL) nuclei 2. Short-term memory 2. Corticomedial (DM) nuclei  Where newly learned information is initially stored (minutes) 3. Central nuclei 3. Long-term memory 4.  Recently learned information are reinforced, conveyed, & 1. Basolateral (ventrolateral) nuclei stored for a prolonged period of time  Receives afferent fibers  Mediated by the hippocampal formation  Phylogenetically the newest  Projects to: Lesions in the hippocampal formation 1. Dorsomedial nucleus (thalamus)  Inability to transfer immediate & short-term memory into 2. Basal nucleus of Meynert long-term memory 3. Ventral striatum  Influences functions of the hypothalamus Learning and Memory processes may be interrupted by: 1. Trauma 2. Corticomedial (Dorsomedial) nuclei 2. Cerebral anoxia  Receives afferent fibers 3. Alzheimer‟s disease  Phylogenetically the oldest 4. Korsakoff‟s syndrome  Terminal of the olfactory fibers - Amnestic confabulatory syndrome involving the  Project to the VL nucleus (hypothalamus) hippocampus.  Play a role in eating behaviors III. AMYGDALA 3. Central Nuclei  Give rise to efferent fibers  Aka: amygdaloid body, amygdala complex, amygdala nuclei  Receives projections from basolateral & corticomedial nuclei  (G. amygdalon, „almond‟)  Gives rise to the Ventral Amygdalofugal Pathway  Almond-shaped group of nuclei deep to the uncus of the  Terminates in the ANS nuclei (brainstem) parahippocampal gyrus  Involved in respiratory & CV functions  Connections with visceral memory and visceral motor nuclei of brainstem in central nuclei. Nucleus Connections Functions  It Is situated partly anterior and partly superior to the tip of Corticomedial *Afferents from Behaviors the inferior horn of the lateral ventricle (dorsomedial) olfactory bulb & associated with  Produces activities associated with feeding and nutrition olfactory cortex hunger & eating when stimulated *Efferents to the VM  May cause rage and aggressive behavior when stimulated nucleus of the  Modulates hypothalamic and endocrine activities hypothalamus  Has the highest concentration of opiate receptors in the brain Basolateral Reciprocally connected *behaviors (Ventrolateral) to the sensory associated with *Bilateral lesions result in placidity, with loss of fear, rage, and associatation cortical eating & drinking aggression areas *Autonomic & *Efferents to MD somatic reflex nucleus of thalamus, activity basal nucleus of *Behavioral Meynert, & ventral reactions to stressful striatum situations Page 5 of 8 PREPARED BY: CMED 1B  (002) LIMBIC SYSTEM DR. ARELLANO | 12/04/2020 Central Reciprocally connected Respiratory & IV. BRAINSTEM CENTERS ASSOCIATED WITH to the visceral sensory Cardiovascular & autonomic nuclei responses LIMBIC SYSTEM FUNCTION (brainstem) Hypothalamus  Mediates ANS (visceral) responses that accompany the Table 4. Nuclei of the Amygdaloid Complex with its connections and expression of emotions functions Thalamus Afferent Projections to the Amygdala:  Hippocampal formation receives afferent fibers from the a. Olfactory bulb anterior, LDm LP, & intralaminar nuclei. b. Orbitofrontal cortex c. Cingulate gyrus Habenular Nuclei d. Basal forebrain  Project to the e. Medial thalamus a. Interpeduncular & raphe nuclei (midbrain) f. Hypothalamus b. Hypothalamus g. Brainstem c. VTA d. SN Efferent Projections from the Amygdala: 1. Stria terminalis Ventral tegmental area (VTA)  Fibers from the corticomedial nucleus to the septal nuclei &  Modulates the processing of memory via dopaminergic fibers hypothalamus  Projects ascending dopaminergic fibers to all limbic  Lies between the thalamus and the caudate nucleus structures. 2. Amygdaloid pathway  Fibers from the central nucleus to the brainstem Locus ceruleus  Fibers from the basolateral nucleus to the thalamus, ventral  Sends noradrenergic fibers striatum, & basal nucleus  Projects ascending noradrenergic fibers to all limbic structures. Connections of the Amygdala Dorsal Raphe Afferent projections to the Efferent projections to the  Sends serotinergic fibers to the limbic system, where they amygdala amygdala modulate the processing of memory Olfactory bulb Hypothalamus Orbitofrontal cortex Septal nuclei Structure Function Cingulate gyrus Ventral striatum Hypothalamic nuclei: Control ANS responses associated with Basal forebrain Nucleus basalis of Meynert - Mammillary nucleus the expression of emotions Medial thalamus - Preoptic nucleus Hypothalamus Thalamic nuclei: Process information from hypothalamus brainstem - Anterior and amygdala Table 5. Connections of the Amygdala - Lateral dorsal - Medial dorsal Relay information to the limbic lobe, Functions of the Amygdala prefrontal, & temporal areas 1. Control of the ANS in relation to previous experiences Habenular Nuclei Serves as relay centers for information  Indirectly: From the amygdala to the hypothalamus arising from the limbic system destined  Directly: From amygdala to the brainstem autonomic centers for the midbrain reticular formation **NOTE: Ventral tegmental area Regulates processing of memory  Corticomedial nucleus projects to the hypothalamus (VTA) (Indirectly) Locus ceruleus Regulates processing of memory  Central nucleus projects to the brainstem (Directly)  Amygdala utilizes fast experiences to modulate the Dorsal raphe Regulates processing of memory autonomic nervous system activity and influences the Table 6. Brainstem Centers associated with the Limbic System and visceral and somatic aspects that correspond to behavioral their functions expression of emotion. V. Pathways of the Limbic System *Precise stereotactlc lesions in the amygdaloid complex in humans reduce emotional excitability and bring about normalization of behavior Alveus in patients with severe disturbances. No loss of memory occurs  Two-way bundle of myelinated axons that gather to become fimbria  Consists of thin layer of white matter that lies on the superor or ventricular surface of the hippocampus. Fimbria  Extends to the sub-splenial area inferior to the corpus callosum Page 6 of 8 PREPARED BY: CMED 1B  (002) LIMBIC SYSTEM DR. ARELLANO | 12/04/2020 Fornix 4. The stimulation of this system will lead to arousal, alertness,  Main output pathway of the hippocampal formation and attentiveness. Destruction of this system will lead to  Carries commissural fibers to the habenular nuclei somnolence or coma Perforant Pathway _________________________  Main cortical input pathway to the hippocampal formation Cingulum 5.Inhibition of serotonin synthesis or destruction of serotonin-  Transmits information that interconnects the surrounding containing neurons in the raphe system will lead to a sleep neocortex disorder called Septohippocampal tract _________________________  Carries fibers that arise from the medial septal nucleus & the 6. The following are types of neurons in the monoaminergic nuclei of the diagonal band of Broca system, except * Ventral amygdalohypothalamic tract a. adrenergic neuron  Main projection pathway from amygdala to the hypothalamus b. cholinergic neuron c. serotonergic neuron Mammillothalamic tract (mammillary fasiculus) d. dopaminergic neuron  Principal output pathway from the hypothalamic mammillary e. none of the above nucleus 7. The neurons are associated with memory decline in Mammillo-interpeduncular tract Alzheimer's disease *  Arises from the mammillary body & terminates in the interpeduncular nucleus a. nucleus accumbens b. nucleus basalis of Meynert Mammillo-tegmental tract c. red nucleus  Arises from the mammillary body & terminates in the d. caudate nucleus midbrain tegmentum e. none of the above Stria terminalis 8. The reticular formation is a mass of neurons and nerve fibers  From the amygdaloid body terminates in the hypothalamus & extending from caudal medulla to the rostral midbrain, stria terminals continuous with the zona incerta (thalamus), intralaminar and reticular nuclei (subthalamus) * True or False Stria medullaris (thalami)  Fibers that interconnect the habenular nucleus with the _________________________ septal nuclei & anterior hypothalamus Anterior commissure 9. The following nuclei belong to the median raphe nuclear group,  Decussating fibers transmitting olfactory information between except * the olfactory bulbs & parahippocampal gyri a. raphe obscurus Diagonal band of broca b. raphe magnus  Fibers from paraolfactory area, terminate in periamygdaloid c. superior central nuclei area (temporal lobe). d. reticulotegmental nucleus e. none of the above Habenulointerpenduncular tract  Arises from the habenular nucleus & terminates in the 10. The following nuclei belong to the medial reticular nuclear interpeduncular nucleus (midbrain) group, except * a. nucleus reticularis gigantocellularis b. nucleus reticularis pontis caudalis c. cuneiform nucleus Test Your Knowledge d. nucleus reticularis pontis oralis 1. It formed a transition border intervening between the e. none of the above diencephalon and the telencephalon _________________________ 2. A process by which knowledge is stored and is retrievable in 11. The following are components of the hippocampal formation, the future except * _________________________ a. dentate gyrus b. dentate nucleus 3. The neuroanatomical basis of emotion c. subiculum d. hippocampus _________________________ e. none of the above Page 7 of 8 PREPARED BY: CMED 1B  (002) LIMBIC SYSTEM DR. ARELLANO | 12/04/2020 12. The following are structures associated with the hippocampal  Snell’s Clinical Neuroanatomy 8th Edition formation, except * a. induseum griseum b. entorhinal cortex c. fasciola cinerea d. septal area e. none of the above 13. The following are layers of the dentate gyrus, except * a. molecular layer b. polymorphic layer c. granule cell layer d. pyramidal cell layer e. none of the above 14. The following are components of the limbic lobe, except * a. hippocampal formation b. subcallosal gyrus c. cingulate gyrus d. parahippocampal gyri e. none of the above 15. A bilateral lesions in the nucleus reticularis pontis caudalis will result in complete elimination of what type of sleep - Paradoxical sleep 16. All about apneustic center in the pons, except * a. increases the depth and duration of expiration b. sends signals for inspiration for long and deep breaths c. inhibited by stretch receptors of the pulmonary muscles d. increases tidal volume e. none of the above 17. The reticular nucleus of thalamus has a role in integrating and gating activities of thalamic nuclei, and uses a neurotransmitter * a. acetylcholine b. dopamine c. GABA d. glutamate e. serotonin 17. C 16. A 15. Paradoxical sleep 14. B 13. D 12. E 11. B 10. C 9. D 8. False 7. B 6. B 5. Insomnia 4. Ascending Reticular Activating System (ARAS) 3. Papez Circuit 2. Memory 1. Limbic Lobe Answer Key REFERENCES  Powerpoint Presentation/Lecture Page 8 of 8 PREPARED BY: CMED 1B