Limbic System 1x PDF

The Limbic System and The Pineal Gland The Limbic System The anatomic substrate underlying behavioral and emotional expression. Plays a role in feeling, feeding, fighting, fleeing, and mating. Expresses itself through the hypothalamus via the autonomic nervous system (ANS). ...

The Limbic System and The Pineal Gland The Limbic System The anatomic substrate underlying behavioral and emotional expression. Plays a role in feeling, feeding, fighting, fleeing, and mating. Expresses itself through the hypothalamus via the autonomic nervous system (ANS).  The Limbic System Limbus is Latin for “border” The term “limbic” was used originally to describe gyri that form a ring or border on the medial surface of the cerebral hemispheres, around the corpus callosum and rostral brainstem. Today, we use the term limbic system to describe both cortical areas (the “limbic lobe”) and subcortical structures, located mainly in the medial and inferior regions of the cerebral hemispheres  Paul Broca 1878: “le grand lobe limbique” (1824-1880): Refers to a ring of gray matter on the medial aspect of the cerebral hemispheres. James Papez 1930’s: defined a limbic system (1883-1958): that might underlie the relationship between emotion and memory (Papez’ circuit). Paul MacLean in 1952 The theory of a “limbic system” as a basis for emotion His the great limbic lobe of Broca (olfactory cortex, prepiriform area, hippocampal gyrus description and hippocampus; parasplenial, cingulate and subcallosal gyri) as well as included “nuclear structures” (amygdala, septal nuclei, “the cortex hypothalamus, epithalamus, anterior thalamic nucleus and parts of the basal contained in ganglia)”.  Textbook inclusion of limbic anatomy Text Amyg Septal CG Hypo Hippo N Acc Papez Olfact Haines x x X x x x x Brodal x x x x x x Nolte x x x x Kiernan x x x x x x Waxman x x x x x Blumfld x x x x x x x x Arslan x x x x x x Martin x x x x x x x x Bear x x Purves x x X x Kandel x x x X x Conn x X x x X x  limbic lobe is going to be consisting of the paratypocampal gyrus. This is the cerebral cortex around the hippocampus. It is going to be consisting of the cingulate gyrus, subcaldosal gyri, and cingulum. It is not a center for a function, but it really integrates DM is going to be having the limbic reciprocal connections, functions all coming and going connections with the orbitofrontal and the prefrontal cortex and hypothalamus. It receives input from amygdala. Major components and connections Orbitofrontal cortex Dorsomedial nucleus of the thalamus Anterior nucleus of the thalamus Septal area Limbic lobe Hippocampal formation Amygdaloid complex (amygdala) Hypothalamus Limbic midbrain nuclei Olfactory areas Midbrain reticular formation  Orbitofrontal cortex Mediates the conscious perception of smell. Has reciprocal connections with the dorsomedial nucleus of the thalamus. Interconnected via the medial forebrain bundle with the septal area and hypothalamic nuclei. Dorsomedial nucleus of the thalamus Has reciprocal connections with the orbitofrontal and prefrontal cortices and the hypothalamus. Receives input from the amygdala. Plays a role in affective behavior and memory. Anterior nucleus of the thalamus Receives input from the mamillary nucleus via the mamillothalamic tract and fornix. Projects to the cingulate gyrus. A major link in the limbic circuit of Papez.  Septal area Consists of a cortical septal area, including the paraterminal gyrus and the subcallosal area. Consists of a subcortical septal area (the septal nuclei), which lies between the septum pellucidum and the anterior commissure. Has reciprocal connections with the hippocampal formation via the fornix. Has reciprocal connections with the hypothalamus via the medial forebrain bundle. Projects via the stria medullaris (thalami) to the habenular nucleus.  Limbic lobe Not a true lobe Rather, the limbic lobe comprises a ring of cortex on the medial surface of the brain, which spans across aspects of the frontal, parietal, and temporal lobes. It consists of the parahippocampal gyrus, the cingulate gyrus, and a continuation of the cingulate gyrus anteriorly and inferiorly, called the subcallosal gyrus These cortical areas are interconnected by a subcortical fiber bundle called the cingulum.  Limbic lobe Includes: -the subcallosal area -the paraterminal gyrus -the cingulate gyrus -isthmus, -the parahippocampal gyrus (including the uncus) -the hippocampal formation and the amygdaloid nuclear complex (buried in the parahippocampal gyrus )  Hippocampal formation Functions in learning, memory, and recognition of novelty. Major input via the entorhinal cortex. Major output via the fornix. Major structures of the hippocampal formation 1-Dentate gyrus has a three-layered archicortex. contains granule cells that receive hippocampal input and project it to the pyramidal cells ofthe hippocampus and subiculum. Major structures of the hippocampal formation 2- Hippocampus (Cornu ammonis): -Has 3 layered cortex -contains pyramidal cells that project via the fornix to the septal area and the hypothalamus -Divided into 4 cytoarchitectural areas (CA1-CA4)  Major structures of the hippocampal formation 3- Subiculum A transition zone of cortex, continuous with the hippocampus on one side and the parahippocampal gyrus on the other side. Receives input via the hippocampal pyramidal cells. Projects via the fornix to the mamillary nuclei and the anterior nucleus of the thalamus. hippocampus is going to subiculum is going to be continuous with the parahippocampal gyrus  Major afferent connections to the hippocampal formation (1) Cerebral association cortices (areas 19, 22, and 7) (2) Septal area (3) Anterior nucleus of the thalamus via the cingulate gyrus, cingulum, and entorhinal cortex  Major efferent connections from the hippocampal formation (1) Mamillary nucleus of the hypothalamus (2) Septal area (3) Anterior nucleus of the thalamus  Amygdaloid complex (amygdala) It attaches emotional significance to a stimulus Underlies the parahippocampal uncus. Produces activities associated with feeding and nutrition when stimulated. May cause rage and aggressive behavior when stimulated. Divided into a corticomedial group and a basolateral group. The corticomedial group receives the central nuclei or medial region of the olfactory input, and the basolateral amygdala is going to be functioning in regulating visceral responses to emotional receives prodigious cortical input. stimuli Through hypothalamus, amygdala is going to be inducing, for example, nauseation. Amygdaloid complex (amygdala) Major afferent connections to the amygdaloid complex from the following structures: (1) Olfactory bulb and olfactory cortex (2) Cerebral cortex (limbic and sensory association cortices) (3) Hypothalamus Amygdaloid complex (amygdala) Major efferent connections from the amygdaloid complex to the following structures: (1) Cerebral cortex (limbic and sensory association cortices) (2) Hypothalamus (3) Brainstem and spinal cord  Hypothalamus A major part of the limbic system that projects to the brainstem and spinal cord  Limbic midbrain nuclei Ventral tegmental area Projects ascending dopaminergic fibers to all limbic structures. ventral tegmental area is rich in dopaminergic fibers and the projection is very important. The projection is going to be providing the mesolimbic and the mesocortical projections. So it is going to be directly involving the limbic functions VTA neurons, they project mainly to the nucleus acumbens and ventral steatum. Ventral steatum is nucleus acumbens, the same places.  Limbic midbrain nuclei Raphe nuclei of the midbrain Project ascending serotonergic fibers to all limbic structures. is believed, or it is known, actually, to function in the pathogenesis of depression, decrease of serotonergic activity. Apart from sleep-wake cycle and so on and so forth, there are all going to be, and together with aggression and cognitive functions, appetite, it functions in all those things  Limbic midbrain nuclei Locus ceruleus Projects ascending noradrenergic fibers to all limbic structures.  Major limbic fiber systems Fornix Stria terminalis Ventral amygdalofugal pathway Stria medullaris (thalami) Diagonal band of Broca Tractus retroflexus (habenulointerpeduncular tract)  Fornix The fornix projects from the hippocampal formation. As you can Projects from the hippocampal formation to the see, it starts from the superior side of the hippocampus, and then this is hippocampus. The fimbria of hypothalamus (mamillary nucleus), the anterior hippocampus gives rise to the fornix. From both sides, these legs, they nucleus of the thalamus, and the septal area. start ascending and try to come close to each other, meaning they Projects from the septal area to the hippocampal deviate towards the medial side, and these regions are going to be formation. called the cruz cruz literally means a leg okay so these are the legs the cruz of fornix then these cruz they are sent up and they divert towards the medial side to come close to each other but they are not close enough and there is going to be an interconnection in between of those places and this is going to be called the commissure of fornix they have produced the body of the fornix at the superior side and at the superior side they are eventually trying to reach the mammillary body so they are getting the information from the hippocampus and they are trying to find the mammillary bodies on both sides  Stria terminalis Lies between the thalamus and the caudate nucleus. Projects from the amygdala to the hypothalamus and the septal area. The red one is the fornix, and it is actually reaching the anterior thalamic nuclei, it is reaching the anterior hypothalamus, septal area, but the real destination is mammillary bodies Ventral amygdalofugal pathway Projects from the amygdala to the hypothalamus, thalamus, brainstem, and spinal cord.  Stria medullaris (thalami) Projects from the septal area to the habenular nucleus.  Diagonal band of Broca Forms the medial border of the anterior perforated substance. Interconnects the amygdaloid nucleus and the septal area.  Tractus retroflexus (habenulointerpeduncular tract) Projects from the habenular nucleus (epithalamus) to the interpeduncular nucleus (midbrain).  Papez circuit In 1937, Dr. James Papez, a neuroanatomist at Cornell University, proposed the idea that the experience of emotion involved reciprocal interactions between the diencephalon and the cerebral cortex. Because emotions reach consciousness, and conscious thoughts can affect emotion, Papez hypothesized that a neural circuit involving the limbic system and specific cortical areas formed the neuroanatomical substrate for emotion.  Papez circuit A circular pathway that interconnects the major limbic structures. Contains the following stations: 1-Hippocampal formation Projects via the fornix to the mamillary nucleus. 2-Mamillary body Projects via the mamillothalamic tract to the anterior nucleus of the thalamus. 3-Anterior nucleus of the thalamus Projects to the cingulate gyrus. Receives the mamillothalamic tract. 4-Cingulate gyrus Projects via the entorhinal cortex to the hippocampal formation  prefrontal cortex, it projects the nucleus accumbens, septal nuclei, hippocampus, and amygdala, everywhere. The Reward Circuitry The prefrontal cortex looks like a simple tool which this system uses to consciously search for food, consciously search for sex, But the thing is, the projection to nucleus accumbens, this nucleus the thing which we use consciously, the accumbens projection from prefrontal cortex, the reasoning of human VTA, meaning the beings, is not a higher center, but it is dopaminergic discharge from merely a tool obeying these things VTA to nucleus accumbens through medial forebrain bundle, is going to be providing pleasure  A small mass that lies in the depression between the superior colliculi  Its base i s attached by the pineal stalk  The ventral lamina ofthe stalk is continuous with the posterior commissure and the dorsal lamina with the habenular commissure  Melatonin secretion