Limbic System PDF

Limbic System Limbic System Circle of Papez (Papez’s Circuit) • • • • • Limbus (L) : Border An intermediate or transitional state, which is a border In this context, the border is between the neocortex and the subcortical structures (diencephalon) Not a separate system but a collection of structu...

Limbic System Limbic System Circle of Papez (Papez’s Circuit) • • • • • Limbus (L) : Border An intermediate or transitional state, which is a border In this context, the border is between the neocortex and the subcortical structures (diencephalon) Not a separate system but a collection of structures Operates by influencing endocrine system & autonomic nervous system Includes: • Orbitofrontal cortex • Hippocampus • Amygdala • Ant thalamic nucleus • Hypothalamus • Basal ganglia Connecting pathways: Alveus Fornix Fimbria Mamillothalamic tract Stria terminalis Limbic System • Behavioral and emotional responses, especially those needed for survival: • • • • • • Feeding Reproduction Caring for our young Fight or flight responses Memory Drive (satiety & hunger) (sexual arousal & reproduction)) (maternal instincts) • The ability to feel and express emotion: Feature observed in a significant number of animals • Humans experience & express large mix emotions → shapes an individual’s behavior • In the context of limbic function, emotion does not refer to “happiness” or “sadness”, but rather drinking when thirsty or a response to a potential mate • Originally defined as a series of cortical structures surrounding the limit between the cerebral hemispheres and the brainstem: the border, or limbus, of the brain; arising from the Latin word limbus, meaning edge. Limbic System Cingulate Gyrus • Begins beneath ant.end of corpus callosum & continues above the corpus callosum until it reaches its posterior end • Separated from corpus callosum by callosal sulcus • Separated from superior frontal gyrus by cingulate sulcus Limbic System Hipocampal Formation Consists of 3 parts: • Hippocampus proper (Ammon’s horn) • Dentate gyrus (fascia dentata) • Subiculum • Located in temporal lobe, medial to inf. horn of lateral ventricle • Ammon: An Egyptian god, near whose temple ammonia or the salt of Ammon was prepared • Hippocampal formation is bundle of grey matter • Hipocampal Formation Limbic System • Medial view - R hippocampal formation • Calcarine sulcus (which leads to the occipital pole) is a useful landmark • Cortical areas that border the hippocampus (e.g., the parahippocampal gyrus) are particulary visible in this view. Limbic System Hipocampus • Named hippocampus bcs resembles a sea horse in coronal section. • Curved elevation of gray matter that extends throughout entire length of floor of inf. horn of lateral ventricle • Ant. end expanded to form pes hippocampus • Convex ventricular surface covered w/ ependyma • Hippocampus terminates posteriorly beneath splenium of corpus callosum Limbic System The alveus • Beneath ventricular surface of hippocampus - thin layer of white matter • Consists of nerve fibers that originated in hippocampus • Fibers converge medially to form bundle called fimbria • Fimbria becomes continuous w/ crus of the fornix Limbic System Dentate Gyrus • Narrow, notched band of gray matter • Lies btwn fimbria of hippocampus & parahippocampal gyrus Limbic System • L temporal lobe w/ inf. horn of lateral ventricle exposed • Transverse section • Post. view of hippocampus on floor of inferior (temporal) horn Limbic System Hipocampal Formation Function • Integrates info from various brain areas and influences endocrine, visceral, and emotional processes via its efferent output • Particulary associated w/establishment of short-term memory • Lesions of the hippocampus can cause specific defects in memory formation • Fiber tract of fornix connects hippocampus to the mammillary body Fornix Limbic System • White matter tract connecting the hippocampus to mammillary bodies • Closely apposed but functionally unrelated to corpus callosum. Picture: Viewed from upper L & ant. aspect. Limbic System Septum pellucidum: • Thin plate stretching btwn corpus callosum & fornix • Forms medial boundary of lateral ventricles • Btwn the 2 septa is a cavity of variable size, cavum septi pellucidi • Cholinergic nuclei in the septa, which are involved in organization of memory, are connected to hippocampus by fornix Limbic System Amygdala (Aka amygdaloid nucleus) • So named bcs it resembles an almond. • Integrative center for emotions, emotional behavior, motivation • Situated anterosuperior to tip of inf horn of lateral ventricle • Fused w/ tip of tail of caudate nucleus, Limbic System Amygdala C • Receives inputs from all senses & visceral inputs • Important in emotional learning ➔ visceral inputs are a major input source • Visceral inputs: • Olfactory sensory input: • Auditory, visual & somatosensory input: Hypothalamus, septal area, orbital cortex & parabrachial nucleus From olfactory bulb. From temporal & anterior cingulate cortices • A part communicates with regions of hypothalamus to regulate fear and anxiety responses • Stimulation of amygdala causes intense emotion, such as aggression or fear Outputs: 1. Ventral amygdalofugal pathway 2. Stria terminalis 3. Directly to the hippocampus 4. Directly to the entorhinal cortex 5. Directly to the dorsomedial nucleus of the thalamus Limbic System C Amygdala & Hippocampus Lesions There is evidence that the hippocampus is concerned with converting recent memory to long-term memory A lesion of the hippocampus results in the individual being unable to store long-term memory. Memory of remote past events before the lesion developed is unaffected. This condition is called anterograde amnesia. Limbic System Hypothalamus • Involved in sexual arousal, emotional response, endocrine regulation, sexual development, thermoregulation, regulation of satiety and hunger, osmoregulation • Feeds information into the limbic system AND serves as its final output • Hippocampohypothalamic fibers connect the hippocampus with the mammillary bodies via the fornix. • Links nervous system to the endocrine system via the pituitary gland (secretes releasing hormones) • Several hypothalamic nuclei are sexually dimorphic Limbic System Circle of Papez (Papez’s Circuit) Summary: Limbic structures are involved in the development of sensations of emotion and with the visceral responses accompanying those emotions and in the control of emotion, behavior, and drive. The hippocampus is concerned with recent memory