Hypothalamus DR M B BHAT Hypothalamus is diencephalic

Hypothalamus DR. M. B. BHAT.

Hypothalamus is diencephalic structure & is developed from anterior or ventral part and base of the diencephalon ¢ Location: The anterior part of the lateral wall of the third ventricle and below & in front of the thalamus containing the hypothalamic nuclei. ¢

Anatomical position ¢ ¢ ¢ Superiorly—by hypothalamic sulcus in the wall of the third ventricle (which separate it from the thalamus above) Rostrally (Anteriorly)—by a plane passing along the anterior commissure and optic chiasma Posteriorly – Mammillary body Laterally—by a plane marking the medial angle of internal capsule, Medially – anterior part of the lateral wall of the third ventricle

Classification of hypothalamic nuclei Anterior group or Supra optic area nuclei 2. Middle group or Tuberal area nuclei 3. Posterior group or Mammillary area nuclei {Among these nuclei, the nuclei located in lateral region are diffuse & the nuclei located in the medial region are more distinct} 1.

Lateral region hypothalamic nuclei are: Lateral pre-optic nucleus; Anterior hypothalamic nucleus (of anterior group); Lateral hypothalamic nucleus (of middle group) & Lateral mammillary body (of posterior group) ¢ Medial group hypothalamic nuclei are: Rest of the hypothalamic nuclei ¢

Anterior group nuclei ¢ ¢ 1. 2. 3. 4. 5. The nuclei located above the optic chiasma They are; Anterior hypothalamic nucleus Pre-optic nuclei (medial & lateral) Supra optic nucleus Supra chiasmatic nucleus Para ventricular nucleus

Middle group nuclei ¢ ¢ ¢ 1. 2. 3. 4. 5. The nuclear mass situated in close relation with infundibulum & tuber cinerium They are; In the medial region – Arcuate nucleus Periventricular nucleus Ventro-medial hypothalamic nucleus (VMH) Dorso-meidal hypothalamic nucleus Lateral hypothalmic nucleus (LH) – of the lateral region

Posterior group nuclei ¢ ¢ 1. 2. The nuclear mass in relation to 3 rd ventricle & mammillary body They are; Posterior hypothalamic nucleus Mammillary bodies

Connections Through Medial Fore-brain bundle (MFB) ¢ Afferent – (mainly goes to lateral hypothalamic area) ¢ Frontal lobe (except area 4); Limbic cortex (Anterior olfactory area, Orbito-frontal area, Piriform cortex) & Amygdala goes to Lateral hypothalamic areas. ¢ Spinal cord & Brain stem Reticular formation goes to Lateral hypothalamic regions ¢ Thalamo-hypothalamic fibers --Reticulum nuclei of thalamus to DMN of hypothalamus (Afferent fibers to medial hypothalamic regions through MFB are going indirectly via lateral hypothalamic regions) 1.

Among these RF afferent fibers of MFB; ¢ Adrenergic fibers from mid-brain RF & medulla goes to Ventral hypothalamus ¢ Nor-adrenergic fibers from – Ø NTS & ventro-lateral nuclei goes to Paraventricular nuclei (forms the ventral bundle of MFB) Ø Locus ceruleus goes to dorsal hypothalamus (forms the dorsal bundle) ¢ Serotonergic fibers from Raphe nucleus goes to posterior hypothalamus ¢

Summary of afferent connections ¢ ¢ ¢ Afferent through MFB goes mainly to lateral hypothalamic regions. Afferent fibers goes to medial hypothalamus via MFB also through lateral hypothalamic area. Stria terminalis (from amygdala) & Medial cortico-hypothalamic tract (from hippocampus) fibers are the only two major afferent pathway running directly to the medial hypothalamus

¢ ¢ ¢ Efferent through MFB– From Posterior hypothalamus descend to mid-brain RF (via medial bundle of MFB with respect of cerebral aqueduct) & also From Lateral hypothalamic area fibers descend to midbrain RF (via lateral bundle of MFB) & From mid-brain RF, these fibers descend to (ventromedio-lateral of) spinal cord & synapses with LH of spinal cord Fibers from periventricular nucleus of hypothalamus goes to DMN of thalamus Ascending fibers from lateral hypothalamus area goes to hippocampus via septum

Through Stria terminalis – Afferent & Efferent connection of VMH with Amygdala & (via from & to) Piriform cortex 3. Through Fornix – ¢ Hippocampus to mammillary body of hypothalamus –Post commissural fibers (part of Papez circuit) ¢ Hippocampus to LH – Pre commissural fibers 2.

Other afferent fibers Medial cortico-hypothalamic tract – Hippocampus to arcuate nucleus ¢ Pallido-hypothalamic tract – from GP to DMN, VMH, Paraventricular & mammillary body of hypothalamus ¢ Retino-hypothalamic tract – optic fibers from retina goes to suprachiasmatic nuclei ¢

Other efferent fibers Ventral pathway –connects LH with amygdala ¢ Mammillo-thalamic tract – mammillary body to AN nucleus of thalamus ¢ Mammillo-tegmental tract – mammillary body to mid-brain RF ¢ Hypothalamo-Hypophyseal tract – Supra optic & Paraventricular nuclei to posterior pituitary ¢ From various hypothalamic nuclei fibers end at median eminence to influence anterior pituitary ¢

Functions of Hypothalamus Regulation of ANS – Control of sympathetic NS –Posterior hypothalamus Control of parasympathetic NS –Middle hypothalamus Influence the vegetative functions –such as Cardio-vascular function, G-I tract function, ¢ Role in sleep – ¢ Posterior hypothalamus (Waking center) ¢ Pre-optic area (Sleep center ¢

Regulation of body temperature – Heat gain center – Posterior hypothalamus Heat loss center – Pre-optic & Anterior nuclei of hypothalamus Thirst center – Pre-optic & Para ventricular nuclei ¢ Role in emotion –Mammillary body ¢ Role in circadian rhythm –Supra-chiasmatic nucleus ¢ Role in sexual control – Arcuate & periventricular nucleus (ventral part of hypothalamus) ¢ Role in posterior pituitary function ¢ Role in anterior pituitary function ¢

¢ ¢ 1. 2. 3. 4. Control of food intake – Feeding center (center for hunger) – LH (Lesion of LH cause anorexia nervosa) Satietary center – VMH (Lesion of VMH produce obesity) Factors stimulate VMH— Lipostatic hypothesis – (Leptin) Gut peptide hypothesis – (GI tract hormones) Glucostatic hypothesis – (blood sugar) Thermostatic hypothesis – (body temperature)

Hypothalamic control of anterior pituitary Para ventricular nucleus – CRH & TRH ¢ Arcuate nuclei – GRH & PIH ¢ Medial pre-optic area – Gn. RH ¢ Periventricular nuclei -- Somatostatin ¢

Disorders of hypothalamus Anorexia nervosa – LH lesion ¢ Obesity – VMH lesion ¢ Sleep disorders – Lesion of posterior nuclei (Narcolepsy, Cataplexy) ¢ Fall in body temperature – lesion of posterior nuclei ¢ Disorders of sexual function ¢ Sympathetic & parasympathetic over reactions ¢ Emotional disorders along with memory ¢

¢ ¢ ¢ Removal hypothalamus produce loss of orientation of space & time, retention of childhood memories, forgetfulness of recent event Some clinical disorders due hypothalamic lesion: Diabetes insipidus – lesion of supra optic Laurence Bidel-Moon syndrome Adipogenitalis dystrophia –chromophobes pituitary tumor cause hypersecretion of ACTH Narcolepsy – lesion of posterior nucleus

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