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Major Fiber tracts of the hypothalamus:-the hypothalamus is extensively interconnected with many portions of the neuraxis: basal forebrain regions

that are components of the limbic system; brainstem regions that serve as part of the autonomic nervoussystem

TractFornix -mammillary bodies of the hypothalamus receive a large axonal projection from the

hippocampus via this pathway-also contains axons that serve as inputs to the hippocampus from various regionsMammillothalamictract

-projects from the mammillary bodies (nuclei) to the anterior nucleus of the thalamus

Stria terminalis -prominent pathway interconnecting the amygdaloid complex with the medial zone of thehypothalamus

Medial forebrainbundle

-the most complex fiber pathway in the CNS containing at least 50 parts-extends through the entire lateral hypothalamic zone interconnecting regiosn from the septalnucleis rostrally to the brainstem caudally

Supraopticohypophyseal tract

-conducts fibers from the supraoptic and paraventricular nuclei to the neurohypophysis

Tuberoinfundibulartract

-conducts fibers from the arcuate nucleus to the hypophyseal portal system at the medianeminence of the infundibulum

Hypothalamospinaltract

-contains descending axons that drive spinal cord preganglionic neurons of both sympatheticand parasympathetic divisions of the autonomic nervous system

Regulatory functions of the hypothalamus-body temp, feeding and energy metabolism, emergency responses to stress, blood pressure and electrolyte

composition, reproductive functions-the hypothalamus functions to integrate autonomic and endocrine functions with behavior especially

behavior concerning basic homeostatic requirements of everyday life

-has internal sensory neurons that are responsive to changes in local temp, osmolarity, and glucose and Naconcentrations

-extensively interconnected with sites of autonomic and endocrine outflow, as well as limbic areas that affectbehavioral responsiveness

-fundamental capacities:1. can access sensory information from virtually the entire body2. establishes biological set points for temperature, blood osmolarity, glucose, sodium, and levels of

hormones3. responds to deviations of set points by adjusting an array of autonomic, endocrine, and behavioral

responses to restore homeostasisThermoregulation

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-neurons in the anterior hypothalamic nucleus are sensitive to warmth and trigger heat dissipation throughmultiple mechanisms such as sweating, cutaneous vascular dilation, and accelerated respiration by activationparasympathetic system

-inflammatory cytokines and pyrogens act on the anterior hypothalamic nucleus to alter body temperature setpoint initiating a fever

-neurons in the posterior hypothalamic nucleus are sensitive to cold triggering heat conservation viasympathetic outflow such as shivering, cessation of sweating, vascular constriction and activation of appropriateendocrine response of the thyroid gland to alter metabolic rate

-both nuclei are under influences from the limbic system-both nuclei are interconnected to the brain stem and spinal cord to mediate their effects-in addition to body responses heat dissipation and conservation are accomplished through behavior changes-bilateral destruction of the anterior nucleus results in hyperthermia-bilateral lesions of posterior nucleus and its surrounding are results in inability to thermoregulate

(poikilothermia)-due to loss of both cold sensitive neurons and warm sensitive descending projections that pass

through this region on way to brainstem

Stress response

-flight or fight response-control of release of stress hormones from the adrenal cortex and EP/NP from the adrenal medulla-sympathetic connections with viscera initiate physiological changes to support an integrated flight or fight

response-diversion of blood from viscera to skin and muscles-increased CO, papillary dilation, bronchodilation, and decreased GI motility and renal activity-inhibits parasympathetics

-hypothalamus is under afferent regulatory control by numerous brain regions such as pre-frontal cortex;;limbic forebrain, and brainstem

-hypothalamus integrates signals from these areas , input from which varies to the nature of thestressor, and produces an appropriate coordinated set of responses involving outflow thru

autonomic, endocrine, and other systems-hippocampus and amygdale from the limbic system are extensively interconnected with the hypothalamus

Feeding and energy metabolism-lateral and ventromedial nuclei are centers for feeding and satiety-arcuate nucleus plays a central role

-two types of neurons with different neuropeptides1. agouti-related peptide and neuropeptide Y: signals increase feeding and decrease metabolism2.POMC and CART-synthesis and release alpha MSH; signals a decrease in feeding and an

increase in metabolism-output of both sets of neurons is integrated in the brainstem nucleus of solitary tract which acts as a

satiety center-involves hormones: insulin, glucagon, leptin, ghrelin, PPY

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-leptin stimulates decrease in eating thru inhibition of AGrP/NPY neurons in arcuate nucleusCraniopharyngioma

-congenital tumor originating from remnants of rathkes pouch-most common supratentorial tumor in children-pressure on optic chiasm results in bitemporal hemianopsia (tunnel vision)-pressure on overlying hypothalamus results in hypothalamic syndrome of adiposity, diabetes insipidus,

temperature regulation disturbances, and somnolence