Nervous - Limbic System and Diencephalon PDF

Nervous: Limbic System & Diencephalon YBOD200 Mr J Naidoo  Learning Objectives Identify, describe and discuss the anatomy with regards to position and relations of the limbic system: o Hypothalamus - its central position to the limbic system, Central gyrus, Amy...

Nervous: Limbic System & Diencephalon YBOD200 Mr J Naidoo  Learning Objectives Identify, describe and discuss the anatomy with regards to position and relations of the limbic system: o Hypothalamus - its central position to the limbic system, Central gyrus, Amygdala, Septal nuclei, Mammillary bodies, Anterior thalamic nuclei, Olfactory bulbs, Fornix, Hippocampus Identify, describe and discuss the anatomy with regards to position and relations of the diencephalon: o Thalamus, Hypothalamus, Infundibulum, Mammillary bodies, Pineal gland  INTRODUCTION Limbic system – portions of brain that turns motivations and physiological drives into behaviours o Contains: ▪ Cortical components – (cingulate and parahippocampal gyri etc.) ▪ Subcortical components – (hippocampus, amygdala etc.) o Structures serve as bridges between autonomic and voluntary responses to changes in environment Diencephalon o Widespread and important connections as majority of sensory, motor and limbic pathways involve a “stop” at diencephalon Limbic System Limbic Structures  Limbic Structures Limbic cortical areas and other limbic components serve as bridges between multimodal association areas and hypothalamus Two major limbic subsystems centred around amygdala and hippocampus, including areas beyond parahippocampal and cingulate gyri Structurally similar cortex extends over uncus and across insula to orbital cortex Hippocampal subsystem users posterior cingulate and parahippocampal cortex as a relay to neocortex and has a close relationship with anterior thalamic nucleus and mammillary body Limbic Structures  Hippocampus Lies above medial part of parahippocampal gyrus Curved elevation, lying along floor of inferior horn of lateral ventricle Associated with dentate gyrus o Anteriorly continues with notch of uncus Subcortical projections to: o Septal nuclei o Mammillary nuclei o Nucleus accumbens o Anterior thalamic nuclei  Septum Pellucidum Midline structure, comprised of fibres, sparse grey matter and neuroglia Below septum pellucidum is septal region: o Contains septal nuclei: dorsal, ventral, medial and caudal groups  Fornix C-shaped white matter tract, lies inferior to septum pellucidum Connects medial temporal lobe to hypothalamus and other limbic structures Divided into: o Crura – related to splenium of corpus callosum o Commissure – commissural fibres o Body o Columns o (Fimbriae) – related to dentate gyrus  Amygdala Collection of about a dozen nuclei Lies beneath uncus, at anterior end of hippocampus and inferior horn of lateral ventricle Merges with periamygdaloid cortex, which forms part of surface of uncus, and parahippocampal gyrus Nuclei are subdivided into medial, central and basolateral groups  Sensory Inputs to Amygdala FOUR ROUTES: 1. Via stria terminalis, situated in wall of lateral ventricle and carrying input from hypothalamus and septal nuclei. 2. Via ventral amygdalofugal pathway, from thalamus and hypothalamus and orbital and anterior cingulate cortex 3. Via lateral olfactory tract, from olfactory bulb and cortex 4. Directly from temporal lobe structures such as neocortex and hippocampus  Projections from Amygdala Fibres also leave amygdala via stria terminalis and ventral amygdalofugal pathway. Fibres in ventral pathway reach the ventral striatum, including area of fusion between putamen and caudate nucleus, and then projects into ventral pallidum beneath anterior commissure. o These link into the basal ganglia and indicate a route in which “emotional-related information” can influence decisions on movement. o Anything expected to be pleasurable also increases release of dopamine in ventral striatum due to projections. Projections from Amygdala Diencephalon  Diencephalon Diencephalon is divided into four parts: o Epithalamus – including pineal gland o Dorsal thalamus – known as thalamus o Subthalamus o Hypothalamus Only portion of diencephalon that can be seen on an intact brain is inferior surface of hypothalamus and mammillary bodies as well as infundibular stalk.  Diencephalon Boundaries: o Superiorly – Body of lateral ventricle o Inferiorly – exposed to subarachnoid space o Caudal – Plane through posterior commissure* o Rostral – Anterior commissure* *Rostral and caudal are descriptive boundaries only  Epithalamus Pineal gland is a midline structure situated rostral to superior colliculus and resembles a pinecone Arises as an evagination from roof of diencephalon Attached to diencephalon via a stalk Due to its location, tumours to this gland compress midbrain – early findings may include hydrocephaly since the cerebral aqueduct would get squeezed shut  Epithalamus Caudally – at base of stalk of pineal gland is posterior commissure Rostrally, on either side is a small swelling – habenula, under which are habenular nuclei o One major input bundle - stria medullaris of thalamus ▪ Fibres originate in globus pallidus and some limbic structures o One major output bundle - habenulointerpeduncular tract (fasciculus retroflexus) ▪ Between habunelar nuclei and interpeduncular nucleus (between cerebral peduncles)  Subthalamus Parts of midbrain tegmentum continue into diencephalon as subthalamus Location: o Inferior to thalamus o Lateral to hypothalamus o Medial to cerebral peduncle and internal capsule Contains: Rostral portions of red nucleus and substantia nigra Subthalamic nucleus – interconnected with basal ganglia Zona incerta – small mass of gray matter between subthalamic nucleus and thalamus. Hypothalamus  Hypothalamus Small portion of diencephalon Involved in pathways concerning autonomic, endocrine, emotional and somatic functions Multiple functioning, based on: o Interconnections with various cortical and subcortical components o Outputs influencing pituitary gland – hormonal changes o Interconnections with various visceral and somatic nuclei of brainstem and spinal cord  Hypothalamus INFERIOR SURFACE: o Exposed directly to subarachnoid space o Bound by optic chiasm, optic tracts and mamillary bodies – this area is known as tuber cinereum Median eminence o Protrudes from tuber cinereum o Continuous with infundibular stalk ▪ Continuous with posterior lobe of pituitary gland  Hypothalamus MEDIAL SURFACE: o Boundaries: ▪ Anterior - lamina terminalis ▪ Superior – hypothalamic sulcus ▪ Posterior - caudal edge of diencephalon Preoptic area – neural tissue that is functionally and structurally continuous with hypothalamus, treated as part of anterior hypothalamus Three regions of hypothalamus: 1. Anterior – above optic chiasm 2. Tuberal – above and including tuber cinereum 3. Posterior – above and including mammillary bodies  Hypothalamus Longitudinal zones of thalamus (transverse section): o Periventricular zone – thin zone, makes up wall of third ventricle; contains suprachiasmatic and arcuate nuclei o Medial zone – has several nuclei, zone overlapping tuberal region contains dorsomedial and ventromedial nuclei o Lateral zone – lateral to fornix, continuation of reticular nucleus Table listing all nuclei in each region and zone of hypothalamus Inputs and Outputs of Limbic System  Inputs to Limbic System Neural inputs to the hypothalamus arise in two general areas: o Various parts of forebrain – relevant information to mediate somatic and autonomic states o Brainstem and spinal cord – afferents conveying visceral and somatic information, via medial forebrain bundle and dorsal longitudinal fasciculus.  Forebrain Inputs Major forebrain afferents to hypothalamus arise from: o Septal nuclei, and nearby parts of basal forebrain as well as ventral striatum ▪ Located adjacent to septum pellucidum o Hippocampus ▪ Fibres located in fornix and go to mammillary body o Amygdala ▪ Projects fibres via two routes: 1. Via stria terminalis, bundle that accompanies caudate nucleus 2. Fibres pass under lentiform nucleus Forebrain Inputs o Insula, and some other related cortical areas ▪ Fibres arise from orbital and medial prefrontal cortex and join medial forebrain bundle (bidirectional, associated with fibres from septal nuclei and fibres from spinal cord on other side) o Retina ▪ Projections from photosensitive retinal ganglion cells to suprachiasmatic nucleus  Hypothalamic Outputs Efferent pathways mostly reflect afferent pathways Projections from hypothalamus to septal nuclei, amygdala, hippocampus, brainstem and spinal cord via same fibre bundles However, efferents to cerebral cortex blanket cortex rather than focusing on limbic areas: o Histaminergic fibres from tuberomammillary nucleus o Orexinergic fibres from tuberal and posterior hypothalamus Thalamus  Thalamus Large, egg-shaped nuclear masses with a posterior appendage. Major relay-station for pathways – each using separate portions of the thalamus, subdividing it into a series of nuclei Borders o Anteriorly: extends to interventricular foramen o Superiorly: transverse cerebral fissure and floor of lateral ventricle o Inferiorly: hypothalamic sulcus o Posteriorly: Overlaps midbrain  Thalamic Nuclei Thin, curved sheet of myelinated fibres – internal medullary lamina, divides thalamus into medial and lateral groups of nuclei. Anteriorly the internal medullary lamina splits and encloses an anterior group – collectively known as anterior nucleus, bordering the interventricular foramen Medial group has a single large nucleus – dorsomedial nucleus Lateral group comprises bulk of thalamus and is further divided into a dorsal and ventral tier.  Thalamic Nuclei Dorsal tier of lateral group: o Lateral dorsal nucleus o Lateral posterior nucleus o Large Pulvinar ▪ Lateral posterior nucleus is continuous with pulvinar Ventral tier of lateral group: o Ventral anterior nucleus o Ventral lateral nucleus o Ventral posterior nucleus ▪ Customary further divided into ventral posterolateral and ventral posteromedial nuclei  Thalamic Nuclei Ventral posteromedial is somatosensory relay nucleus for the head. Ventral posterolateral is somatosensory relay nucleus for the body. Medial geniculate and lateral geniculate nuclei are located posterior to the ventral tier nuclei and inferior to the pulvinar, protruding posteriorly along the midbrain. Medial – Auditory Lateral - Visual Thalamic Nuclei Thalamus  Thalamus An additional layer of cells cover the medial surface of the thalamus and form the midline nuclei of thalamus, which fuse in thalamic adhesion. Internal medullary lamina also splits at other locations and encloses other nuclei, collectively termed intralaminar nuclei – this together with the midline nuclei project to widespread areas of the cortex. Lateral surface of thalamus covered by a second sheet of myelinated fibres – external medullary lamina o Cells that lie between this lamina and the internal capsule forms the thalamic reticular nucleus – this projects to other thalamic nuclei and not the cortex. Relay Station That’s All Folks! For any queries or questions please feel free to contact me: [email protected]  RESOURCES Nolte’s The Human Brain, 8th Edition Chapter 16 The Thalamus and Internal Capsule: Getting to and From the Cerebral Cortex https://www.clinicalkey.com/student/content/book/3-s2.0-B9780323653985000163 Chapter 23 Drives and Emotions : The Hypothalamus and Limbic System - Nolte's The Human Brain https://www.clinicalkey.com/student/content/book/3-s2.0-B9780323653985000230 Gray's Clinical Neuroanatomy: The Anatomic Basis for Clinical Neuroscience Chapter 16 Cerebral Hemispheres https://www.clinicalkey.com/student/content/book/3-s2.0- B9781416047056000168#hl0000685 The Fornix: Functional Anatomy, Normal Neuroimaging, and Various Pathological Conditions Choi et al., 2021 https://doi.org/10.13104/imri.2021.25.2.59