Limbic System

Limbic System The term "limbic" is from the Latin word Limbus, for "border" or "edge". The limbic system is a set of primitive brain structures located on top of the brainstem and buried under the cortex It separates the medial surface of the cerebral cortex from diencephalon

Limbic System The limbic system consists of a number of cortical & subcortical structures with complex and often looped connections that all project to the hypothalamus.

Limbic System Components The limbic system includes: 1. Limbic lobe. 2. Hippocampal formation. 3.Septal area. 4.Prefrontal area. 5. Amygdala 6. Anterior thalamic nuclei 7. Hypothalamus (mammillary body) 8. Fornix 9.Olfactory system. 10. Habenular nuclei 1 8 4 6 10 3 7 9 2 5 1

Limbic Lobe C-shaped ring of grey matter on the medial side of each cerebral hemisphere, surrounding the corpus callosum. It includes: Subcallosal area Cingulate gyrus Isthmus Parahippocampal gyrus Uncus. 2 1 3 5 4

Hippocampus It is a seahorse shaped paired structure, one in each hemisphere. Located in the inferomedial part of the temporal lobe. Involved in formation, organization, storage and retrieval of memory

The fornix is an important component of PAPEZ CIRCUIT Its principal efferent projection is to the mammillary body via a C-shaped bundle of fibers called the Fornix. Fornix consists of: Fimbria Crus Body Column The fornix is an important component of PAPEZ CIRCUIT 3 2 4 1

Papez Circuit In 1937: Papez was the first to describe a relationship between limbic system components. Papez’s circuit connects the parahippocampal gyrus, hippocampus, fornix, mamillary body, anterior thalamic nucelus and cingulate gyrus. Since the initial description, connections to additional subcortical structures have been identified.

Hippocampal Formation The hippocampal formation is a compound structure in the medial temporal lobe of the brain It consists of: Hippocampus Dentate gyrus: Which lies between hippocampus & Parahippocampal gyrus. Subiculum (at the base of the hippocampus) Entorhinal area (area 28) Indusium griseum (grey matter on the upper surface of the corpus callosum). Indusium griseum Fornix Entorhinal area Hippocampus Dentate gyrus

The entorhinal cortex is part of the medial temporal lobe or hippocampal memory system and constitutes the major gateway between the hippocampal formation and the neocortex. The name entorhinal (inside rhinal) cortex derives from the fact that it is partially enclosed by the rhinal (olfactory) sulcus.

Amygdala Almond shaped mass of nuclei, lies near the temporal pole, close to the tail of the caudate nucleus It is the behavior awareness area which is responsible for the behavioral response appropriate to each occasion. Connections: Input: from association areas of visual, auditory & somatosensory cortices. Output: to hypothalamus & brainstem autonomic nuclei, to control the autonomic centers.

Amygdala Function: It is involved in emotional responses, fear, anger, hormonal secretions, and memory. Relate environmental stimuli to coordinated behavioral autonomic and endocrine responses seen in species-preservation. Responses include: Feeding and drinking Agnostic (fighting) behavior Mating and maternal care Responses to physical or emotional stresses.

Amygdaloid lesions Voracious appetite Increased (perverse) sexual activity Docility: Loss of normal fear/anger response Memory loss: Alzheimer`s ??? lack of emotional responses

Septal Nuclei Site: Located anterior to the interventricular foramen below the rostrum of corpus callosum Main connections: To hypothalamus through medial forebrain bundle. To habenular nuclei through stria medullaris thalami. Function: It provides critical interconnections and it is the pleasure zone. Septal area

Interventricular foramen

Fornix The Fornix -Made up of fibres arising from hippocampus Septum pellucidum The Fornix -Made up of fibres arising from hippocampus -Body of the fornix is suspended from corpus callosum by septum pellucidum -Posteriorly,divides into two crura. -The crura are interconnected by fibres passing from one another forming hippocampal commissure. Anterior commissure

Fornix

Habenular nuclei Located in habenular triangle (area in the posterior part of the diencephalon, just anterior to pineal gland) Have connections with limbic system Serves autonomic function and emotional drives

Functions of Limbic system Energy and water balance Autonomic functions Temperature Endocrine functions Sexual behavior Emotional behavior Learning and memory

Limbic Lobe Disorders Korsakoff’s psychosis (Retrograde & anterogdrade amnesia) Temporal lobe epilepsy: The hippocampus is a common focus site in epilepsy, and can be damaged through chronic seizures. Alzheimer’s disease: The hippocampus is one of the first brain areas to show damage in Alzheimer's disease The hippocampus is sometimes damaged in diseases such as herpes encephalitis & Schizophrenia.