Limbic system

A presentation with details on limbic system of human brain - anatomy, functions etc.

1. LIMBIC SYSTEM : Neuroanatomy and Functions PURNIMA KARTHA. N

2. CONTENTS Limbic System – Introduction. History Functions of the Limbic System Anatomy: Subcortical Structures : Amyglada , Hypothalamus, Thalamus, Septal Region. Limbic Cortex: Limbic Lobe, Hippocampal Formation. Routes of Communication Related Nerve Fibres Reference. 2

3. LIMBIC SYSTEM The term limbic system has been used to refer to the entire neuronal circuitry that controls emotional behavior and motivational drives . The limbic system includes a ring of forebrain structures that surround the brain stem and are interconnected by intricate neuron pathways. The word “ limbic ” means “ border .” 3

4. HISTORY 1937- James Papez first proposed that specific brain circuits are devoted to emotional experience and expression. 1850s - Paul Broca - used the term “limbic lobe” (part of the cerebral cortex that forms a rim around the corpus callosum and diencephalon) 4

5. FUNCTIONS OF THE LIMBIC SYSTEM Integration of olfactory, visceral and somatic impulses reaching the brain Control of activities necessary for the survival of the animal , including procurement of food and eating behaviour. Control of activities necessary for the survival of species - including sexual behaviour Establishing emotional states : pain, pleasure, docility, affection, and anger Facilitation memory storage and retrieval 5

6. ANATOMY The anatomical structures of the limbic system consists of an interconnected complex of basal brain elements. 6

7. PARTS OF THE LIMBIC SYSTEM 7

8. SUBCORTICAL STRUCTURES Hypothalamus Hippocampus (Ammon’s horn) along with the dentate gyrus . Amygdaloid nuclei Septal nuclei Paraolfatory areas Anterior nuclei of the thalamus. Portions of the basal ganglia. 8

9. AMYGDALOID NUCLEAR COMPLEX Also called amygdaloid body or amygdala . Lies in the temporal lobe of the cerebral hemisphere, close to the temporal pole. It lies deep to the uncus and is related to the anterior end of the inferior horn of the lateral ventricle. 9

10. LOCATION OF AMYGDALA Superiorly, the complex is related to the anterior part of the lentiform nucleus Inferiorly, the complex is related to the anterior most part of parahippocampal gyrus It fuses with the anterior end of the tail of the caudate nucleus . The lower end of the stria terminalis lies in relation to the amygdaloid complex. 10

11. In the region between the amygdaloid complex and the lentiform nucleus, there is a region of substriatal grey matter, within which there is a collection of cholinergic neurons. These neurons form the Basal nucleus of Meynert . Amyglada is also divided into 3 groups of nuclei : 11

12. The amygdala receives afferent (input) fibers from the olfactory bulb, orbitofrontal cortex, cingulate gyrus, basal forebrain, medial thalamus, hypothalamus, and brainstem. Efferent fibres from amygdala pass through two major routes: Stria terminalis (which conveys fibers primarily from the corticomedial nucleus to the septal nuclei and the hypothalamus) Ventral amygdalofugal route (which also conveys input fibers to the amygdala) The limbic system projections to the deep cerebral nuclei are associated with underlying emotional aspects that influence movement. 12

13. FUNCTIONS Important role in the control of emotional behaviour . Reciprocal projections between the amygdala & thalamus, hypothalamus, septal nuclei, orbital frontal cortex, cingulate gyrus , hippocampus, parahippocampal gyrus , and brain stem modulate ANS activity and endocrine responses . Coordinated responses to stress and anxiety and integrates many behavioral reactions. Stimulation of the amygdala produces behavioral arousal and can produce directed rage reactions. 13

14. HYPOTHALAMUS The hypothalamus, which represents less than 1% brain mass, is one of the most important of the control pathways of the limbic system. It has two-way communicating pathways with all levels of the limbic system it and its closely allied structures Controls most vegetative and endocrine functions of the body as well as emotional behavior . 14 H

15. FUNCTIONS Cardiovascular Regulation Regulation of Body Temperature Regulation of Body Water Regulation of Uterine Contractility and of Milk Ejection from the Breasts. Gastrointestinal and Feeding Regulation Hypothalamic Control of Endocrine Hormone Secretion by the Anterior Pituitary Gland. 15

16. BEHAVIOURAL FUNCTIONS Stimulation of lateral hypothalamus increases the general level of activity of the animal, sometimes leading to overt rage and fighting. Stimulation in the ventromedial nucleus and surrounding areas causes opposite effects - a sense of satiety , decreased eating , and tranquility . Stimulation of a thin zone of periventricular nuclei , located immediately adjacent to the third ventricle leads to fear and punishment reactions . Sexual drive can be stimulated from several areas of the hypothalamus, especially the most anterior and most posterior portions of the hypothalamus. 16

17. THALAMUS The amygdala and hypothalamus project to the “limbic nuclei” of the thalamus, which include the anterior nuclear group and the lateral dorsal and medial dorsal nuclei of the thalamus. These nuclei then relay this information to the limbic lobe. 17

18. SEPTAL REGION Masses of grey matter that lie immediately anterior to the lamina terminalis and the anterior commissure. The cerebral cortex of this region shows two small vertical sulci called the anterior and posterior para -olfactory sulci . The region between the anterior and posterior parolfactory sulci is the subcallosal area (or parolfactory gyrus ). The cortex of this region is referred to as the septal area in distinction to the septal nuclei , which lie deep to the cortex. 18

19. LIMBIC LOBE Bordering the limbic cortex – Perilimbic areas. Limbic lobe is composed of a ring of cerebral cortex in each side of the brain orbitofrontal area subcallosal gyrus cingulate gyrus parahippocamal gyrus Uncus 19

20. HIPPOCAMPAL FORMATION Hippocampal formation includes hippocampus dentate gyrus gyrus fasciolaris indusium griseum medial and lateral longitudinal striae 20

21. HIPPOCAMPUS The hippocampus is an infolding of the cerebral cortex, embedded within the parahippocampal gyrus of the temporal lobe The hippocampus extends from the amygdala anteriorly, and then tapers as it courses posteriorly to the inferior surface of the splenium of the corpus callosum . At its anterior extent, the hippocampus displays a swelling with several grooves resembling a paw, and is thus referred to as the pes hippocampus. 21

22. Indusium griseum : thin layer of grey matter, lining the upper surface of the corpus callosum in the hippocampal formation. Within the IG - embedded two bundles of longitudinally running fibres called the medial and lateral longitudinal striae . IG continuous with a thin layer of grey matter related to the inferior aspect of the splenium of the corpus callosum: splenial gyrus or gyrus fasciolaris The splenial gyrus runs forwards to become continuous with the dentate gyrus , ( in the inferior horn of the lateral ventricle). 22

23. Papez Circuit Hippocampus receives fibres mainly from entorhinal area , amyglada and cingulate gyrus. The fornix is the main efferent tract of the hippocampus. Commissure of fornix/hippocampal commisure S eptal and anterior hypothalamic regions Mammillary body (which sends impulses to cingulate gyrus through anterior nucleus of thalamus, through Papez circuit) 23

24. FUNCTION Hippocampus provides the drive that causes translation of short-term memory into long-term memory ( Long-term potentiation ). 24

25. ROUTES OF COMMUNICATION An important route of communication between the limbic system and the brain stem is the medial forebrain bundle , which extends from the septal and orbitofrontal regions of the cerebral cortex downward through the middle of the hypothalamus to the brain stem reticular formation. This bundle carries fibers in both directions, forming a trunk line communication system. A second route of communication is through short pathways among the reticular formation of the brain stem, thalamus, hypothalamus, and most other contiguous areas of the basal brain. 25

26. RELATED FIBRE BUNDLES Olfactory nerves, tract and striae . Fornix, stria terminalis , stria medullaris thalami , diagonal band, and anterior commissure. 26

27. REFERENCE Atlas of Functional Neuroanatomy 2nd Edition - Walter J. Hendelman Inderbir Singh's T extbook of Human Neuroanatomy (9 th edition) - Pritha S Bhuiyan , Lakshmi Rajgopal , K Shyamkishore A Textbook of Neuroanatomy - Maria A. Patestas , Leslie P. Gartner Textbook of Medical Physiology (11 th edition) - Arthur C. Guyton, John E. Hall. Principles of Anatomy & Physiology(13 th Edition) -Gerard J. Tortora , Bryan Derrickson . 27