Limbic System and Hypothalamus PDF

LIMBIC SYSTEM AND HYPOTHALAMUS Class Year 2, Semester 1 Lecturer DR. VIJAYALAKSHMI S B Department of Anatomy Email id: [email protected] Date 3/11/2024 1 LEARNING OUTCOMES Describe the anatomical component...

LIMBIC SYSTEM AND HYPOTHALAMUS Class Year 2, Semester 1 Lecturer DR. VIJAYALAKSHMI S B Department of Anatomy Email id: [email protected] Date 3/11/2024 1 LEARNING OUTCOMES Describe the anatomical components of the limbic system Describe the position and functions of the hypothalamus Describe the position, relations and functions of the pituitary gland Explain the role of the limbic system in memory Describe some of the consequences of limbic component malfunction OVERVIEW LEVEL OF PROCESSING “Societal Societal Homeostasis Homeostasis based homeostasis” based based on external on internal inputs on external inputs at a inputs at a higher-order basic/survival level association  HYPOTHALAMUS Pituitary stalk Optic chiasm Mammillary bodies Hypothalamus CN III CN IV Crus cerebri Interpeduncular fossa Pons hypothalamus HYPOTHALAMIC NUCLEI HYPOTHALAMUS Integrates signals from internal organs and fluid-filled cavities and maintains homeostasis using its input and output systems Part of diencephalon Pituitary gland hangs from it Inputs arrive via: 1. Blood (i.e., hormonal) 2. Brainstem (i.e., neural) Output is mediated through: 1. Pituitary gland (hormonal and neural) 2. Limbic system (neural) FUNCTIONS OF HYPOTHALAMUS Fluid & Electrolytes Food Ingestion Thermoregulation Reproduction Immune responses Circadian rhythms Emotional responses (brain centre for regulation of the autonomic nervous system) HYPOTHALAMIC INPUTS Blood Neural Sampled in the hypothalamus Nucleus solitarius (medulla) Physical Baroreceptors Temperature chemoreceptors osmolality Reticular formation Chemical (medulla & pons) glucose diffuse set of information acid-base pertaining to the state of neural arousal Hormones Limbic Growth and development Action (fight/flight, sex Thalamus hormones)  HYPOTHALAMIC OUTPUTS Blood Neural Direct hormone production Autonomic nervous system vasopressin (ADH) Thermoregulation oxytocin Fight or flight Control of pituitary gland Appetite & thirst hypophyseal portal system Limbic System connects the two Initiate appropriate (instinctive) releasing factors motor behavioural responses anti-releasing factors Limbic part of basal ganglia  HYPOTHALAMIC HORMONAL OUTPUTS Hormone production Release in neurohypophysis!!! SUPRAOPTIC N. Hypothalamus Vasopressin (ADH) Hypophyseal Portal system Activated by osmoreceptors (if osmolality increases) PARAVENTRICULAR N. Oxytocin Mammary gland milk production Uterine muscle contraction  HYPOTHALAMIC HORMONAL OUTPUTS To anterior pituitary (adenohypophysis) MEDIAN EMINENCE Releasing Factors Hypothalamus Hypophyseal Portal system Anti-releasing factors HYPOTHALAMIC/PITUITARY TUMOURS Endocrine problems: over- or under-production of circulating hormones. Excess Prolactin = infertile Excess Cortisol = Cushing’s syndrome appearance, osteoporosis, weakness, diabetes Hypoadrenalism/Adrenal insufficiency = Addison’s disease hyperpigmentation, low BP, tachycardia Growth disorders (e.g., dwarfism, gigantism, acromegaly) Sexual function (e.g., hypogonadism, precocious puberty) Body water control (e.g., diabetes insipidus, pathological drinking) Eating (e.g., obesity and bulimia) Pressure effects: compression of posteromedial aspect of optic chiasmas can result in bitemporal visual field loss  LIMBIC SYSTEM Arched border area between neocortex and diencephalic structures, thalamus and hypothalamus Components: Cingulate gyrus Hippocampal formation Fornix Mamillary bodies Septal nuclei N. accumbens Amygdala  LIMBIC SYSTEM cingulate gyrus fornyx fornix corpus Corpus thalamus callosum collosum hypothalamus mamillary body LIMBIC SYSTEM Mamillary bodies  LIMBIC SYSTEM Anatomically, the limbic structures include the cingulate gyrus, Parahippocampal gyrus, hippocampal formation, amygdaloid nucleus, mammillary bodies and anterior thalamic nucleus The alveus, the fimbria, the fornix, the mammillothalamic tract and the stria terminalis constitute the connecting pathways  17 INPUT-OUTPUT RELATIONSHIP OF LIMBIC SYSTEM MAJOR FUNCTIONS Influence many aspects of Emotional behavior Converting recent memory to long-term memory Provide pathways for the integration and effective homeostatic responses to a wide variety of environmental stimuli  LIMBIC SYSTEM AND MEMORY Anterior Nucleus of the thalamus Cingulate gyrus Corpus callosum Medial Dorsal Nucleus of the thalamus contributes to Nucleus accumbens memory Mamillary body Contributes to episodic memory formation Make new Decides on how memories memories are made PAPEZ CIRCUIT PAPEZ CIRCUIT HIPPOCAMPAL FORMATION Consists of: Hippocampus, Dentate gyrus Part of the Parahippocampal gyrus Receives Ipsilateral afferents from the inferior temporal cortex via entorhinal cortex Contralateral afferents from hippocampus and entorhinal cortex via fornix and hippocampal commissure Efferent pathway: Fornix  HIPPOCAMPUS Location: Inferomedial to the floor of Inferior Horn of Lateral Ventricle; On the medial surface of Temporal Lobe “HIPPOCAMPUS” = SEAHORSE  CLINICAL ASPECTS - ALZHEIMER’S DISEASE Hippocampal degeneration (bilateral) – cannot form new memories Anterograde amnesia for recent events Loss of episodic memory New autobiographical memory affected  OTHER CORTICAL DEGENERATIONS Fronto-temporal dementia - Prefrontal cortex degeneration inappropriate behaviour & later attention and motivation deficit Semantic dementia - Atrophy of middle and inferior temporal neocortex. Patients progressively lose meaning of words and perception of the world. Memory of autobiographical experiences (episodic memory) relatively preserved as hippocampus not primarily affected FORNIX  FORNIX Efferent from Hippocampus Cingulate gyrus Corpus callosum Efferent fibres from the hippocampus form fimbria Partial decussation at crus Nucleus accumbens Mamillary body → two bundles of fibres (anterior and posterior) Posterior: to Mamillary bodies Body (short-term memories and smell - near nasal fibers) Ant Pillars Anterior: Septal nuclei and N. accumbens Crus Hippocampal commissure Hippocampus Fimbria  NUCLEUS ACCUMBENS & SEPTAL AREA Cingulate gyrus Reward and Reinforcement Corpus callosum Nucleus Accumbens Stimulation – sense of well-being via: dopaminergic activity Nucleus accumbens Mamillary body cocaine inhibits the reuptake of dopamine, so dopamine floods the medial forebrain amphetamines stimulate dopamine release Connection to basal nuclei motor expression of emotion Septal area: Stimulation – sensation like orgasm Destruction = RAGE!!  AMYGDALA Cingulate gyrus Location - At the tip of tail of Corpus callosum the caudate nucleus and inferior horn of the lateral ventricle (at the anterior pole of temporal lobe) Nucleus accumbens Stimulation causes intense Mamillary body emotions, e.g., fear, aggression Fear – important for survival Overactivity – rage Role in phobias Bilateral ablation – complete calmness, hypersexuality. MEMORY AND LEARNING Reward Centres (“medial forebrain bundle” – septal nuclei, nucleus accumbens, olfactory regions and brainstem) Punishment Centres (Periaqueductal grey, thalamus, amygdala, hippocampus) Reward/Punishment – learning Repetition – Habituation  CLINICAL ASPECTS Wernicke-Korsakoff syndrome Memory disorder – patient displays amnesia (memory loss) of both anterograde and retrograde memory Typically associated with the toxic effects of alcohol or from a Vitamin B1 (thiamine) deficiency. Neurons in the hippocampal formation and other parts of the Papez circuit are particularly affected Korsakoff's syndrome is often, but not always, preceded by an episode of Wernicke encephalopathy, which is an acute brain reaction to a severe lack of thiamine. Korsakoff psychosis – recovers but – Memory loss – Cannot form new memories  Bilateral lesions in CLINICAL ASPECTS mammillary bodies Wernicke encephalopathy Alcoholism→ Severe thiamine (B1) deficiency “Dry beriberi” with peripheral neuropathy + microhemorrhages in tegmentum, cerebellar vermis and mammillary bodies TRIAD OF → Ocular palsy nystagmus (Cr. N 6) Ataxia (cerebellum) Confusion (mammillary body) Hemorrhage in “Eyes rolling”, mammillary bodies “Man rolling”, “Mind rolling”  CLINICAL ASPECTS MRI Kluver-Bucy Syndrome Following bilateral anterior temporal lobectomy, including amygdala No fear, Excessive tameness, flat affect Agnosia, oral exploration Indiscriminate dietary behaviour Autoeroticism and sexual mounting on inanimate objects Anterograde amnesia if hippocampi are involved Bilateral lesions of anterior temporal lobes and amygdalae following a concussion Amygdala-rage (Amer J Emer Med 2003) Electrical Stimulation of Amygdala Targeted rage Rage lasts long after stimulation Amygdala-Rage is seen in Temporal Lobe Epilepsy REFERENCES PRACTICE QUESTIONS