neuro2(2) - 883 Hypothalamus HYPOTHALAMUS Introduction The...

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Hypothalamus 883 HYPOTHALAMUS Introduction The hypothalamus is a very small, but extremely important part of the diencephalon that is involved in the mediation of endocrine , autonomic and behavioral functions. The hypothalamus: (1) controls the release of 8 major hormones by the hypophysis, and is involved in (2) temperature regulation, (3) control of food and water intake, (4) sexual behavior and reproduction, (5) control of daily cycles in physiological state and behavior, and (6) mediation of emotional responses. A large number of nuclei and fiber tracts have been described in the hypothalamus. Some of these are ill-defined and have no known function, while others have been studied in detail both anatomically and physiologically. This handout will attempt to focus your attention on the significant and interesting aspects of the structure and function of the hypothalamus. The hypothalamus is the ventral-most part of the diencephalon. As seen in Fig. 2 of the thalamus handout , the hypothalamus is on either side of the third ventricle, with the hypothalamic sulcus delineating its dorsal border. The ventral aspect of the hypothalamus is exposed on the base of the brain (Fig. 1). It extends from the rostral limit of the optic chiasm to the caudal limit of the mammillary bodies . 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 (Fig. 1) Important components of the 3 rostral to caudal regions of the hypothalamus are as follows: Supraoptic Region . In the supraoptic region (above the optic chiasm) there are a number of named nuclei, the most prominent being the supraoptic and paraventricular (Fig. 2A). Neither of these two nuclei is large, but each is easily recognized because it is made up of relatively large, deeply staining cells. The cells in these two nuclei secrete vasopressin (ADH , antidiuretic hormone), oxytocin, and CRH (corticotropin releasing hormone). ADH and oxytocin are transported down the axons from cells in the supraoptic and paraventricular nuclei through the infundibulum to the neurohypophysis (posterior pituitary), where they are released into the blood stream (Fig. 3A). This pathway is termed the supraopticohypophysial tract. Damage to the anterior hypothalamus blocks the production of ADH, resulting in diabetes insipidus , which is characterized by rapid water loss from the kidneys. CRH is released by the paraventricular and taken up by the portal system where it has its action on the anterior lobe of the pituitary. A recent, interesting development is the finding of a direct projection from the eye to the suprachiasmatic nucleus
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This note was uploaded on 01/16/2012 for the course BI 200 taught by Professor Potter during the Fall '11 term at Montgomery College.

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neuro2(2) - 883 Hypothalamus HYPOTHALAMUS Introduction The...

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