1. Boundaries of the hypothalamus
Dorsal – ventral nuclei of the thalamus
Ventral – bottom of the brain
Medial – third ventricle
Anterior – to lamina terminalis below anterior commissure
Posterior – line between mammillary bodies and posterior commissure
Lateral – lateral nucleus of hypothalamus
- tuber cinereum is area between mammillary bodies and optic chiasm/tracts
- infundibular stalk connects median eminence (protrudes from surface of tuber cinereum) and
pituitary
Landmarks for zones
Anterior zone – part above optic chiasm
Tuberal zone – part above and including tuber cinereum
Posterior zone– part above and including mammillary bodies
Medial zone/Lateral zone – divided by a parasagittal plane through the fornix as this fiber
bundle traverses the hypothalamus
2. Major pathways through which hypothalamus is interconnected with forebrain and with
brainstem and spinal cord
- Hypothalamus sends output, gets input from nucleus of solitary tract (visceral input, output
via vagus/parasympathetic functions)
- Hypothalamus projects to rostral ventral medulla controlling input to sympathetic nervous
system
Inputs/Outputs are reciprocal
Hypothalamus:
- connected with brainstem via dorsal longitudinal fasciculus
- connected with brainstem/spinal cord via medial forebrain bundle
- connected with cortex, septum via medial forebrain bundle
- connected with amygdala via stria terminalis and ventral route
- connected with hippocampal formation via fornix
3. Principal routes through which the hypothalamus influences the pituitary gland
- secretion of neuropeptides into general circulation via the posterior pituitary (direct);
- secretion of releasing factors into portal plexus  influences production and release of
hormones form the anterior pituitary (indirect)
- large neurons in supraoptic and paraventricular nuclei (anterior hypothalamus) secrete
oxytocin and vasopressin  transport it down axons that traverse infundibular stalk  release
in posterior pituitary (magnocellular neurosecretory system)
- anterior pituitary controlled by smaller, parvocellular neurons in walls/floor of 3rd ventricle
 these secrete releasing hormones or release-inhibiting hormones in median eminence 
access to hypophyseal portal system  reach anterior pituitary
4. Organization in hypothalamus of warm-sensitive and cold-sensitive neurons and heatconservation and heat-retention areas
- hypothalamus is a survival/propagation tool
- hypothalamic function involves servomechanism – some regulated parameter is compared to a
desired value called a set point
- human body temperature has a set point  once difference between ambient temperature and
set point passes TH value  hypothalamic control sets in until difference is reduced
- internal thermostat located in anterior hypothalamus and preoptic area; contains two
populations of temperature-sensitive neurons: warm-sensitive and cold-sensitive
- if temp of blood passing by anterior/preoptic hypothalamus increases  preoptic area 
heat-dissipation mechanisms including sweating, vasodilation, and behavioral responses
(finding cool place)
- info about diminished core temperature  medial forebrain bundle  posterior
hypothalamus  activation of heat-conserving and heat-generating mechanisms including
shivering, vasoconstriction, metabolic changes, and behavioral responses (finding warmer place,
closing window)
-thermoregulator areas of hypothalamus affect endocrine mechanisms that affect body
temperature, such as thyroid and adrenal stimulating hormones; effect mediated by
hypothalamic-hypophyseal system (vascular system that carries regulating factors from
hypothalamus to pituitary gland)
5. Regulation of thirst and drinking behavior
- signals that water needs to be consumed or conserved come from increased tissue osmolality
and decreased blood volume
- increasing body water can be accomplished by drinking more or excreting less
- anterior hypothalamic neurons are directly sensitive to tissue osmolality  send info about
increased osmolality to supraoptic/paraventricular nuclei  increased vasopressin (ADH)
secretion  increase water resorption from kidney; these neurons are called osmoreceptors
(located in region rostral to 3rd ventricle)
- OVLT (organum vasculosum of the lamina terminalis): circumventricular organs (lacks bloodbrain barrier); contains osmoreceptive neurons; OVLT  output to medial preoptic nucleus 
to lateral hypothalamus  activate motor programs related to drinking behavior via
connections to basal ganglia and brainstem reticular nuclei; similar outputs to limbic structures
for more complex drinking behaviors
- Medial preoptic area  contains osmoreceptive neurons; this region receives info from
baroreceptors in heart about blood volume and from internal organs via nucleus of solitary
tract
- decreased blood volume  stimulates vascular receptors  direct info to hypothalamus via
nucleus of solitary tract; humoral message by activating renin-angiotensin system 
angiotensin in blood reached brain  subfornical organ (SFO) is circumventricular living in
ceiling of third ventricle under fornix  stimulates drinking behavior via output to medial
preoptic region
- osmotic/volumetric thirst describes loss of water from intracellular/intravascular fluid
compartments
6. Circadian rhythms
- many set points oscillate with a period of 24 hours
- circadian rhythms for body temperature, hormone levels, activity, and sleep-wake cycle
- master clock for these rhythms resides in a tiny hypothalamic nucleus called the
suprachiasmatic nucleus, which is above the optic chiasm; its natural period is a bit longer
than 24 hours, but direct retinal input entrains the period to 24 hours