HYPOTHALAMUS The hypothalamus is a very small but

HYPOTHALAMUS The hypothalamus is a very small, but extremely important part of the diencephalon that is involved in the mediation of : Øendocrine, Øautonomic and Øbehavioural functions.

General information Part of diencephalon Weighs about 4 grams The whole brain weighs 1 400 grams Occupies the bottom and infero-lateral walls of the 3 rd ventricle

The Diencephalon

The Diencephalon f ix n or thalamus Epithalamus (Pineal & Habenula) hypothalamus Optic chiasm pituitary Mammillary body subthalamus

Hypothalamus Hypothalami c sulcus Anterior commissure Lamina terminalis Mamillary Optic chiasma body

Hypothalamus 3. Superiorly: hypothalamic sulcus Position: lies ventral to thalamus Boundaries 1. Anteriorly: Lamina terminalis i ii iii 4. Inferiorly: i. optic chiasma, ii. tuber cinereum, infundibulum, and iii. mamillary body 2. Posterior: continues with midbrain tegmentum

Organization In the sagittal plane, it is customary to divide the hypothalamus into three regions: These are from medial (3 rd Vent. ) to lateral: 1. Periventricular, 2. Medial, and 3. Lateral In the coronal plane, the hypothalamus can be divided into: 1. Anterior (supraoptic), 2. Middle (tuberal), and 3. Posterior (mammillary). Since in a deep plane the structures in in the SO region extend beyond the lamina terminalis, therefore the preoptic region is also included in hypothalamus

Divisions of the Hypothalamus

Three rostral to caudal regions are distinguished in the hypothalamus that correspond to three prominent features on its ventral surface: 1) The supraoptic or anterior region at the level of the optic chiasm, 2) the tuberal or middle region at the level of the tuber cinereum (also known as the median eminence—the bulge from which the infundibulum extends to the hypophysis), and 3) the mammillary or posterior region at the level of the mammillary bodies

Hypothalamus Chiasma opticum 1 2 3 Infundibulum (median eminence) Tuber cinereum Mamillary body Optic tract Ventral view

Preoptic, Supraoptic, Anterior Suprachiasmatic, chiasmatic Anterior, Paraventricular Dorsomedial Middle Ventromedial Tuberal Arcuate Nucleus Posterior Caudal Mamillary Mammilary Medial Forebrain Bundle Lateral Zone Fornix 3 rd Ventricle Periventricular zone Medial Zone

Hypothalamic Connections 1. Receives indirect sensory inputs from all sensory systems 2. Sends neural outputs to various motor control nuclei 3. Sends neural outputs to sympathetic and parasympathetic nervous systems 4. Sends both neural and hormonal outputs to pituitary

MAJOR CONNECTIONS OF HYPOTHALAMUS LIMBIC SYSTEM 1. MEDIAL FOREBRAIN BUNDLE septal nuclei, olfactory regions HYPOTHALAMUS & brain stem 2. FORNIX Hippocampal Complex Mammillary Bodies of Hypothalamus 3. STRIA TERMINALIS Amygdala Hypothalamus 4. MAMMILLOTHALAMIC TRACT Hypothalamus Thalamus (anterior nucleus)

AUTONOMIC CONNECTION 5. DORSAL (posterior) LONGITUDINAL FASCICULUS Hypothalamus Brain Stem Reticular Formation Hypothalamus Brain Stem Nuc (e. g. Vagus) Intermediolateral Cell Column ENDOCRINE CONNECTIONS 6. HYPOTHALAMOHYPOPHYSIAL TRACT Hypothalamus Neurohypophysis 7. Tuberoinfundibular Tuberal Nuclei Tract Sinusoids, Portal Veins Adenohypophysis

Hypothalamus Functions

Neural Influences Hormonal Influences The Hypothalamus Autonomic Nervous System Limbic System Endocrine System

Functions of the Hypothalamus �Autonomic nervous system regulation �Hormone production �Endocrine regulation �Circadian rhythm regulation �Limbic system interaction �Various �Temperature regulation �Feeding

Functions of the Hypothalamus 1. Autonomic nervous system regulation Anterior area influences PSNS through projections to brainstem PSNS nuclei Posterior area influences SNS through projections to the lateral gray horn

Functions of the Hypothalamus 2. Hormone production Supraoptic and paraventricular nuclei produce oxytocin and vasopressin (ADH) Transported via axonal transport systems (hypothalamohypophysial tract) to neurohypophysis Released in circulation Clinical Correlate Ø Damage to supraoptic n. diabetes insipidus

Functions of the Hypothalamus 3. Endocrine regulation Stimulating or inhibiting hormones are transported via the tuberoinfundibular tract and released in to the pituitary portal system and ultimately to the adenohypophysis

Functions of the Hypothalamus 4. Circadian rhythm regulation Input from retina to suprachiasmatic nucleus is then sent through poorly defined projections to the pineal gland

Functions of the Hypothalamus 5. Limbic system interaction Preservation of species securing food, defense mechanisms, sexual behavior Emotions Affective behavior Memory Motivation Mammillary body

Functions of the Hypothalamus 6. Various Temperature regulation Feeding Temperature Posterior n. conserves heat Anterior n. dissipates heat Fever starts – sweating Fever ends – chills Feeding Lateral n. induces eating Ventromedial n. inhibits eating

ADENOHYPOPHYSIS Connected with the hypothalamus via the hypophyseal portal system NEUROHYPOPHYSIS Connected with the hypothalamus via the hypophyseal tract

Tubero-infundibular tract

Posterior Pituitary Hormones Antidiuretic hormone (ADH) or vasopressin and Oxytocin synthesized primarily in the supraoptic nuclei & Paraventricular nuclei of the hypothalamus Hypothalamohypop hysial tract

Anterior ( Supraoptic ) Region Preoptic Nucleus Control of parasympathetic function Supraoptic Nucleus Synthesis and secretion of vasopressin. Damage causes diabetes insipidus. Suprachiasmatic Nucleus Fibers from the retina; fibers to the pineal body. Controls circadian rhythms. Anterior Nucleus Controls temperature and sexual behavior. Paraventricular Nucleus Synthesis and secretion of oxytocin (milk secretion & uterine contraction). Controls food intake

Middle or Tuberal Dorsomedial Nucleus - center of satiety - on stimulation rage, cruelty Ventromedial Nucleus - center of satiety - on stimulation depression of appetite Arcuate Nucleus - periventricular in tuber cinereum - secretes releasing-factors - dopaminergic neurons inhibit release of prolactin

Posterior or Mamillary Region Mamillary Nucleus - impulses from hippocampal formation via fornix - impulses from tegmental nuclei, nuclei raphae via mamillary peduncle - projections to anterior thalamic nucleus via mamillothalamic peduncle Nucleus posterior - controls thermoregulation (preserving temperature and producing heat) - damage causes poikilothermia – inability of thermoregulation

Lateral zone Crossed by Medial forebrain bundle Contains two nuclei: 1. lateral preoptic Nucleus 2. lateral hypothalamic Nucleus Clinical Correlate - when stimulated feeling of hunger - when destroyed anorexia nervosa and fast

Neurotransmitters in the Hypothalamus The hypothalamus has been referred to as a “pharmacological museum” by virtue of the plethora of neurotransmitters that it contains. The list of putative neurotransmitters includes: v ACh, v. GABA, vglutamate, vserotonin, vdopamine, and vnorepinephrine as well as literally dozens of peptides that have been identified in recent years.

SUMMARY Dorsomedial

MAJOR FIBER TRACTS OF HYPOTHALAMUS

Lesions of VMN leads to morbid obesity Lesion of lateral hypothalamic area leads to starvation

The hypothalamus is supplied with blood by small branches of the Circle of Willis

Diabetes Insipidus Damage to the anterior hypothalamus blocks the production of ADH, resulting in diabetes insipidus, which is characterized by rapid water loss from the kidneys.

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