Anatomy Of The Limbic System PDF

LECTURER: EDEM EDEM D E P A R T M E N T O F A N AT O M Y ABUAD  OBJECTIVES Describe the basic morphology of the structures comprising the limbic system Describe the input-output relationships of limbic nuclei Describe the functions of the limbic...

LECTURER: EDEM EDEM D E P A R T M E N T O F A N AT O M Y ABUAD  OBJECTIVES Describe the basic morphology of the structures comprising the limbic system Describe the input-output relationships of limbic nuclei Describe the functions of the limbic brain structures Understand the functional and structural bases for clinical and Choose the incorrect option(s)… About the brainstem: It lies medially and inferiorly and is continuous inferiorly with the cervical spinal cord at the foramen magnum. Its fibers connect the PNS and CNS Blood supply: from the vestibulocochlear system CN nuclei of CN I – X originate from this stem  The Limbic System Is the brain’s emotional powerhouse Maintains body homeostasis Controls fight/flight/fright response Forms and retrieves memories  THE LIMBIC SYSTEM It is affected in many neuropsyc hiatric diseases including schizophre nia, Alzheimer’ s disease and some forms of COMPOSITION OF THE LIMBIC SYSTEM The limbic system comprises: – The hippocampal formation – Septal area – Amygdala – Prefronral cortex – Cingulate gyrus These limbic structures directly or indirectly communicate with the hypothalamus and midbrain PAG A critical function of the limbic system is to regulate functions associated with the hypothalamus and/or PAG MY LIMBIC SYSTEM MUST BE IN OVERDRIVE Information flow to and from the limbic system. THE HIPPOCAMPUS  THE HIPPOCAMPAL FORMATION The hippocampal formation is a prominent C-shaped structure bulging in the floor of the temporal horn of the lateral ventricle It consists of:  Hippocampus (sea horse)  Dentate gyrus (tooth-like bump)  Subicular cortex: pre and THE HIPPOCAMPAL FORMATION THE HIPPOCAMPAL FORMATION  THE HIPPOCAMPUS Hippocampus means sea horse Also described to look like ram’s horns – Cornu Amonis- Amun’s horns (CA) subfields  THE HIPPOCAMPUS The hippocampus can be viewed as a layered cortical tissue. Extending from the ventricular surface to the dentate gyrus, we have: (1) External Plexiform Layer  Situated adjacent to the inferior horn of the lateral ventricle  Contains axons of pyramidal cells and hippocampal afferent fibers from the entorhinal cortex (i.e., the alvear pathway);  THE HIPPOCAMPUS (2) Stratum Oriens  Contains basal dendrites and basket cells (3) Pyramidal Cell Layer  Contains the pyramidal cells of the hippocampus (4) Stratum Radiatum and (5) Stratum Lacunosum-moleculare  Last two layers contain the apical dendrites of the pyramidal cells and hippocampal afferents from the entorhinal cortex  THE HIPPOCAMPUS The pyramidal cells of the hippocampus are arranged in a C-shaped fashion, which is interlocked with another C- shaped arrangement of the dentate gyrus. The hippocampus is divided into a number of distinct fields: CA1, CA2, CA3, and CA4. The pyramidal cells situated closest to the subiculum are referred to as the CA1 field, whereas the CA4 field is located within THE HIPPOCAMPUS THE HIPPOCAMPUS THE HIPPOCAMPUS CA4  DENTATE GYRUS The dentate gyrus is also multilayered: (1) Granular Cell Layer  Granule cells are the principal cells  Their axons (Mossy fibres) synapse with CA3 pyramidal cells (2) Polymorphic Cell Layer  Composed of modified pyramidal cells  Lies deep to the granule cell layer. (3) Molecular cell layer  Is apposed to the molecular layer of the hip…  Contains mainly axons of hippocampal afferent fibers. DENTATE GYRUS  SUBICULUM A transitional region between the entorhinal cortex and hippocampus. The primary histological distinction between the hippocampus and subicular cortex is a thicker pyramidal cell layer.  AFFERENT CONNECTIONS OF THE HIPPOCAMPAL FORMATION The entorhinal cortex is a major source of inputs Different groups of fibres arise from the entorhinal cortex laterally and medially  Lateral perforant pathway Into the ML of the hippocampus  Medial perforant pathway Into the alveus through the white matter adjoining the subiculum and ending as the fornix Prefrontal cortex, anterior cingulate gyrus, premammillary region, brainstem  EFFERENT CONNECTIONS OF THE HIPPOCAMPAL FORMATION Efferent fibres arise from pyramidal cells from hippocampus and the subiculum Axons of these cells contribute to the fornix massiveness Thus, 3 components of the fornix system exist in the hippocampal formation  The Pre-commissural Fornix Passes rostral to the ant.commissure and supplies the septal area  The Post-commissural Fornix Innervates the diencephalon  Commissural component Connects the hippocampi Has clinical significance  PYRAMIDAL CELLS Pyramid-shaped Conical-shape cell body of over 30um with an apex directed towards the surface Cylindrical axons arise from the bases of the cells & pass down into the underlying white matter. They are output cells Betz cells – largest, giant pyramidal cells  FUNCTIONS AND DYSFUNCTIONS OF THE H.F Modulation of different functions:  Learning and memory  Aggressive behaviour  Autonomic and endocrine functions  Alzheimer’s disease******* THANK YOU FOR THE MEMORIES!  THE SEPTAL AREA The histological appearance of the septal area differs between humans and other animals. In animals, there exists a dorsal septal area: – Carries the lateral and medial septal nuclei. In humans, a dorsal septal area is not present, only a ventral septal area. Two cell groups are sometimes associated with the septal area: – (1) the bed nucleus, and – (2) the nucleus accumbens, close to the Band of Broca  AFFERENT CONNECTIONS TO THE S.A. The septal area receives sensory afferent fibres from the: Medial olfactory stria Monoaminergic systems of the brainstem Hippocampal formation Amygdala, and Feedback signals from the lateral hypothalamus. The septal area serves principally as a relay of the hippocampal formation to the hypothalamus.  EFFERENT CONNECTIONS FROM THE S.A. The primary efferent projections of the septal area are directed on the hypothalamus and hippocampal formation Fibres to the hypothalamus arise primarily from the lateral septal nucleus The hippocampal formation uses the septal area as a relay nucleus to modulate functions of the hypothalamus The nuclei of the diagonal band of Broca have widespread connections with other parts of the limbic system: – Olfactory, – Prefrontal – Anterior cingulate cortices – Amygdala – Mammillary bodies – Habenular complex, and – Mediodorsal thalamic nucleus  FUNCTION OF THE SEPTAL AREA It serves not only as a relay for the transmission of hippocampal impulses to the hypothalamus, but also as a feedback system to the hippocampal formation. Functions of the septal area are highly similar to those of the hippocampal formation. Like the hippocampal formation, the septal area has been implicated in the control of functions normally attributable to the hypothalamus, such as aggression, rage, autonomic functions, self- stimulation, and drinking behaviour. Septal rage.  I PRESENT TO YOU… THE MOTHER OF EMOTIONS AND DRAMAS  AMYGDALA In humans, the amygdala is located deep to the uncus It comprises various nuclei, which differ in their anatomical connections and neurochemical and physiological properties. The amygdala contains a cortical mantle called the pyriform lobe that provides significant input to the amygdala The major groups of nuclei include the: Lateral Basal Medial Anterior Central and  AMYGDALA Functionally, the amygdaloid complex is divided into two components: – (1) A Corticomedial Group Comprises the cortical, medial, and medial aspect of the basal nuclei – (2) A Basolateral Group, Comprises the lateral, central, and lateral aspects of the basal nuclei The amygdala is intimately related to the pyriform lobe. The cortex immediately adjacent to the amygdala at rostral levels of this structure is referred to as the prepyriform area, and more posterior regions of the pyriform lobe are referred to as the periamygdaloid cortex. THE AMYGDALOID COMPLEX  AFFERENT CONNECTIONS TO THE AMYGDALA Like the hippocampal formation, the amygdala receives inputs from sensory and monoaminergic systems. Afferent fibres to the amygdala arise from structures linked with transmission of both olfactory and taste signals. – Olfactory bulb (direct) – Pyriform lobe (indirect) – Solitary nucleus. From the neocortex: – Auditory signals from the temporal neocortex – Integrative signals from the prefrontal cortex. Additional regions of Ventromedial hypothalamus Substantia innominate Nuclei of the diagonal band of Broca Medial thalamus. EFFERENT CONNECTIONS FROM THE AMYGDALA Hypothalamus Bed nucleus of the stria terminalis Midbrain PAG. Prefrontal cortex (reciprocal  FUNCTIONS AND DYSFUNCTIONS The most significant projections of the amygdala are those that innervate the hypothalamus, bed nucleus of the stria terminalis, and midbrain PAG These projections are deemed to be highly significant because they provide the anatomical substrate by which the amygdala regulates visceral processes normally associated with these structures – Aggressive behaviour – Rage – Impulsivity – Fear/anxiety – Hypersexuality – Relief, relaxation…  FUNCTIONS AND DYSFUNCTIONS Urbach-Wiethe disease (Lipoid proteinosis: – Calcification of the temporal lobe along with the amygdala – Loss of stimuli of fearfulness Me: False! Emotions are from the limbic system, you nitwit!  THE PREFRONTAL CORTEX The PFC experiences a significant evolutionary changes Largest in relative size in humans, thus an increasing understanding of its role It is associated with emotional and intellectual processes – inhibits aggression and rage behaviour elicited by the hypothalamus A technique called prefrontal lobotomy was developed in 1936 by Egaz Moniz for controlling human violence and manifestations of psychotic behaviours  ANTERIOR CINGULATE GYRUS Anterior cingulate gyrus also plays an important role in the regulation of visceral processes, which are, in part, associated with the hypothalamus. For example, electrical stimulation of the ACG suppresses predatory attack behaviour from the lateral hypothalamus, produces respiratory arrest, fall in BP, cardiac slowing Lesions produce aggressive responses A CLINICAL CASE… Just go read your notes!