limbic.pptx

limbic system

1. THE LIMBIC SYSTEM

2. THE LIMBIC SYSTEM

3. THE LIMBIC SYSTEM . The limbic system is the part of the brain involved the behavioral and emotional responses,especially when it comes to behaviours that are needed for survival: feeding,reproduction and caring for young ,and fight or flight responses.

4. STRUCTURES OF THE LIMBIC SYSTEM There are several important structures within the limbic system : The amygdala, hippocampus, thalamus, hypothalamus, basal ganglia ,and cingulate gyrus.The limbic system is among the oldest parts of the in evolutionary terms. Location : the limbic system is located within the cerebrum of the brain,immediately below the temporal lobes,and buried under the cerebral cortex.The cortex is the outermost part of the brain.

5. Function : the structures and interacting areas of th limbic system are involved in motivation, emotion, learning , and memory. The limbic system is where the subcortical structures meet the cerebral cortex. It operates by influencing the endocrine and the autonomic nervous systems. Th e primary structures within the limbic system include : the amygdala , hippocampus, thalamus , hypothalamus, basal ganglia, and cingulate gyrus. A mygdala : It processes reflexive emotions like fear and anxiety.

6. Cerebellum :Functions in the area of movement Cingulate gyrus : Plays a role in processing conscious emotional experience Hippocampus : Plays a principal role in the formation of long-tem memories Thalamus : A main relay station between the senses and the cortex Limbic (border) system is a complex system of cortical and subcortical structures that form a ring around the hilus of cerebral hemisphere.

7. Limbus means ring .It is also called limbic lobe . Earlier ,it was called rhinencephalon (Rhino-Nose). In terms of evolutionary development(phylogeny),limbic system is one of the oldest parts of the brain and it is related to olfactory lobe . Limbic system is primarily concerned with memory. Components of the limbic system Structures of limbic system are classified into four groups : 1.Archicortical structures

8. 2.Paleocortical structures 3.Juxtallocortical structures 4.Subcortical structures. Archicortical structures Archicortex forms allocortex along with paleocortex . Archicortex is phylogenetically the oldest structure . It is concerned with memory.

9. Paleocortical structures: Paleocortex is in between archicortex and neocortex . It is concerned with olfaction. Juxtallocortical structures : Juxtallocortex or mesocortex is situated between paleocortex and neocortex Subcortical Structures Structures situated below the level of cortex are called subcortical structures.

10. Components of Limbic system Archicortical structures consist of : Hippocampus Dentate gyrus Paleocortical structures consist : Piriform cortex Olfactory lobe Olfactory tubercle.

11. Juxtallocortical structures consist of : Cingulate gyrus of limbic cortex Orbitoinsulotemporal cortex Subcortical structures consist of : Amygdaloid complex e. Caudate Septal nuclei f. Reticular formation of midbrain Thalamic nuclei Hypothalamic nuclei

12. Connections of limbic System Connections of the limbic system are complex.The following are the principal (afferent &efferent) connections of limbic system. Fornix :It includes fibres connecting : Hippocampus and septal nuclei with the mamilary body Hippocampus with hypothalamic nuclei 2.Lateral hypothalamus receives afferent fibres from : Hippocampus Septal nuclei

13. c. Olfactory tubercle d. Head of caudate nucleus e. Piriformis f. Periamygdaloid arera 3.Caudate nucleus receives fibres from : Cingulate gyrus Intralaminal nuclei of thalamus

14. 4.Brain stem reticulate formation receives fibres from : Hippocampus Cingulate gyrus PAPEZ CIRCUIT Thi s is the interconnections between various structures of limbic system,which form a complex of closed circuit. This circuit was described by Papez . Hippocampus is connected to mammillary bodies of hypothalamus via formix

15. Mamillary bodies are connected to anterior thalamic nucleus via mamilothalamic tract . Anterior thalamic nucleus is projected into cingulate gyrus through medial thalamocortical fibres . Cingulate gyrus is in turn connected to hippocampus. Papez circuit plays a role in memory encoding . FUNCTIONS OF LIMBIC SYSTEM Limbic system performs the following functions : Analysis of the olfactory signals(amygdala) Control of feeding behaviors

16. c. Control of emotions of fear and rage d. Controls the motivational state e.g response to reward and punishment. e. Acquisition of recent memory ( hippocampus ) f. It makes learning possible ( hippocampus ) g. Control of sexual behavior Limbic system stimulation produces autonomic effects especially, changes in blood pressure heart rate and respiration. Stimulation od amygdaloid nuclei cause rage,fear,reactions of reward and pleasure

17. and pleasure and increased sexual activities such as erection ,copulatory movements,ejaculation,ovulation,uterine activity and premature labour . The limbic system operating through the hypothalamus and anterior pituitary gland can control the rates of secretion of all the sex hormones ,which together control the various sexual drives of the person. The integrity of the limbic system is essential for both long term and short term memory.

18. Damage to the hippocampus causes the most severe amnesia (loss of memory).Patients who have had bilateral removal of portions of the hippocampus find it difficult to learn new information that is based on verbal communication. The principal problem is that though they understand what is being said,they cannot retain the information for more than a few seconds or at least a minute or two. So,they have lost the ability ability to establish short or long term memories.This makes learning of new information impossible.This is termed anterograde amnesia .

19. The limbic system has been extensively studied in humans using electric stimulation of specific areas within it.After stimulation of some areas,the person seems pleased and behaves as if he or she is expecting a reward, stimulation of other areas cause the human to stop the behavior he or she is performing to prevent being punished. In order words,sensations can be pleasant or unpleasant, reward or punishment, or satisfaction or aversion.Electrical stimulation of certain limbic areas pleases or satisfies the person,whereas electrical stimulation of other regions bring about terror,pain,fear,defense,escape reactions,and all the other elements of punishment.

20. zones The degree of stimulation of these two oppositely responding systems greatly affect human behaviour . Reward centres :By using the above procedure,the major reward centres have been found to be located along the course of the medial forebrain bundle,especially , in the lateral and ventromedial nuclei of the hypothalamus. Punishment centres :After the technique,the most potent areas for punishment and escape tendencies have been found in the central gray area surrounding the aqueduct of sylvius in the mes encephalon and extending upward into the periventricular zones of the hypothalamus and thalamus.

21. Less potent punishment areas are found in some locations in the amygdala and hippocampus.