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   REVIEW OF CLINICAL AND FUNCTIONAL NEUROSCIENCE - SWENSON   
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   Introduction   
   The Hypothalamus   
   The Amygdala   
   The Hippocampus   
   Limbic Cortex   
   Chapter 9 - Limbic System   
   The limbic system is a convenient way of describing several functionally and   
   anatomically interconnected nuclei and cortical structures that are located in   
   the telencephalon and diencephalon. These nuclei serve several functions,   
   however most have to do    
   with control of functions necessary for self preservation and species   
   preservation. They regulate autonomic and endocrine function, particularly in   
   response to emotional stimuli. They set the level of arousal and are involved   
   in motivation and    
   reinforcing behaviors. Additionally, many of these areas are critical to   
   particular types of memory. Some of these regions are closely connected to the   
   olfactory system, since this system is critical to survival of many species.   
   Areas that are typically included in the limbic system fall into two   
   categories. Some of these are subcortical structures, while many are portions   
   of the cerebral cortex. Cortical regions that are involved in the limbic   
   system include the hippocampus as    
   well as areas of neocortex including the insular cortex, orbital frontal   
   cortex, subcallosal gyrus, cingulate gyrus and parahippocampal gyrus. This   
   cortex has been termed the "limbic lobe" because it makes a rim surrounding   
   the corpus callosum, following    
   the lateral ventricle. Subcortical portions of the limbic system include the   
   olfactory bulb, hypothalamus, amygdala, septal nuclei and some thalamic   
   nuclei, including the anterior nucleus and possibly the dorsomedial nucleus.   
   One way in which the limbic system has been conceptualized is as the "feeling   
   and reacting brain" that is interposed between the "thinking brain" and the   
   output mechanisms of the nervous system. In this construct, the limbic system   
   is usually under    
   control of the "thinking brain" but obviously can react on its own.   
   Additionally, the limbic system has its input and processing side (the limbic   
   cortex, amygdala and hippocampus) and an output side (the septal nuclei and   
   hypothalamus). Most of these    
   regions are connected by pathways that are shown in figure 31.   
   Hypothalmus   
   The hypothalamus, the primary output node for the limbic system, has many   
   important connections. It is connected with the frontal lobes, septal nuclei   
   and the brain stem reticular formation via the medial forebrain bundle. It   
   also receives inputs from    
   the hippocampus via the fornix and the amygdala via two pathways (ventral   
   amygdalofugal pathway and stria terminalis). The hypothalamus has centers   
   involved in sexual function, endocrine function, behavioral function and   
   autonomic control.   
   In order to perform its essential functions, the hypothalamus requires several   
   types of inputs. There are inputs from most of the body as well as from   
   olfaction, the viscera and the retina. It also has internal sensors for   
   temperature, osmolarity,    
   glucose and sodium concentration. In addition, there are receptors for various   
   internal signals, particularly hormones. These include steroid hormones, and   
   other hormones as well as internal signals (such as hormones involved in   
   appetite control such as    
   leptin and orexin).   
   The hypothalamus strongly influences many functions including autonomics,   
   endocrine functions and behaviors. Autonomic functions are controlled via   
   projections to the brain stem and spinal cord. There are localized areas in   
   the hypothalamus that will    
   activate the sympathetic nervous system and some that will increase   
   parasympathetic activity. Endocrine functions are controlled either by direct   
   axonal connections to the posterior pituitary gland (vasopressin and oxytocin   
   control) or via release of    
   releasing factors into the hypothalamic-hypophyseal portal system (to   
   influence anterior pituitary function). There are also projections to the   
   reticular formation that are involved in certain behaviors, particularly   
   emotional reactions.   
   Some functions are intrinsic to the hypothalamus. These are functions that   
   require a direct input to the hypothalamus and where the response is generated   
   directly via hypothalamic outputs. Included are such things as temperature and   
   osmolarity regulation.   
    There are many functions where the hypothalamus monitors the internal melieu   
   and produces a regulatory response. These include the regulation of endocrine   
   functions and appetite. For example, the ventromedial nucleus of the   
   hypothalamus is considered a    
   satiety area, while the lateral hypothalamic area is a feeding center.   
   Additionally, there are many complex behaviors that are patterned by the   
   hypothalamus, including sexual responses. The preoptic area is one of the   
   areas of greatest sexual dimorphism (i.e., difference in structure between the   
   sexes) and, along with the    
   septal nuclei, is an area of gonadotropin releasing hormone projections to the   
   median eminence region of the hypothalamus. These sexual responses involve   
   autonomic, endocrine and behavioral responses.   
   Finally, the suprachiasmatic nucleus receives direct retinal input. This   
   nucleus is responsible for entraining circadian rhythms to the day-night cycle.   
   Amygdala   
   The amygdala is an important structure located in the anterior temporal lobe   
   within the uncus. The amygdala makes reciprocal connections with many brain   
   regions (figure 32) including the thalamus, hypothalamus, septal nuclei,   
   orbital frontal cortex,    
   cingulate gyrus, hippocampus, parahippocampal gyrus, and brain stem. The   
   olfactory bulb is the only area that makes input to the amygdala and does not   
   receive reciprocal projections from the amygdala.   
   The amygdala is a critical center for coordinating behavioral, autonomic and   
   endocrine responses to environmental stimuli, especially those with emotional   
   content. It is important to the coordinated responses to stress and integrates   
   many behavioral    
   reactions involved in the survival of the individual or of the species,   
   particularly to stress and anxiety. Lesions of the amygdala reduce responses   
   to stress, particularly conditioned emotional responses. Stimulation of the   
   amygdala produces behavioral    
   arousal and can produce directed rage reactions.   
      
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