The Hypothalamus
Hypothalamic Boundaries
• Anteriorly- lamina terminalis, with anterior commissure above and the
optic chiasm below.
• Posteriorly - interpeduncular fossa.
• Dorsally -hypothalamic sulcus, marking the junction with the
• Ventrally -tuber cinereum, which tapers into the infundibulum.
Zones of Hypothalamus
•Hypothalamus is usually divided into 3 zones:
•Lateral Zone
•Medial Zone
•Periventricular Zone
Hypothalamic Nuclei
Hypothalamic Nuclei
• Preoptic nuclei regulate:
– Temperature, heart rate, blood pressure and bladder control
• supraoptic nucleus release antidiuretic hormone (vasopressin)
• paraventricular nucleus - antidiuretic hormone, oxytocin, water
• ventromedial nucleus controls satiety
• lateral hypothalamic nucleus /area - hunger, thirst, blood
pressure, heart rate
• suprachiasmatic nucleus - circadian rhythms
Functions of Hypothalamus
Autonomic Nervous System Regulation
Hormone Production
Endocrine Regulation
Control of Circadian Rhythm
Interaction with Limbic System
Temperature Regulation and Feeding
Control of Autonomic Functions
ANS regulation by hypothalamus: the hypothalamus makes up 1% of brain
volume but controls temperature regulation, heart rate, blood pressure, blood
osmolarity, food and water intake, emotion and sex drives.
Hypophyseal Regulation
• Adenohypophysis (anterior pituitary) – hormone releasing factors,
inhibiting factors
• Neurohypophysis (posterior pituitary) – oxytocin, ADH/vasopressin
Hypothalamic Hypophyseal System
Cardiovascular Regulation
• Lateral hypothalamic nucleus – excitatory cardiovascular center–
increases arterial pressure, heart rate
• Posterior hypothalamic nucleus and preoptic nucleus – inhibitory
cardiovascular center – decreases arterial pressure, heart rate
• Both effects mediated through cardiovascular control centers in
reticular regions of medulla and pons
Respiratory Regulation
• Respiration – Medullary centers (CO2, O2, H+ receptors in
• Urination and defecation – spinal reflexes modulated through higher
centers, especially the cortex
• Hunger
– Ventromedial hypothalamic nucleus – “satiety” center
– Lateral hypothalamic area – hunger center
– Glucose receptors
• Thirst
– Stimuli: cell dehydration, body fluid volume changes
Hypothalamic Control of Food Intake
Hypothalamic Control of Food Intake
• Lesions in ventromedial hypothalamic nuclei produce voracious
appetite (and rage) and obesity.
• The ventromedial nucleus is believed to be the satiety center.
• Lesions to the lateral hypothalamic area abolishes the urge to eat (loss
of appetite) resulting in anorexia and emaciation.
• This area is thought to be the hunger center
• Receptors: Osmoreceptors, stretch receptors
– Roles of ADH, renin/angiotensin
Water Balance and Drinking
• Water deprivation
– Cell dehydration (intracellular volume decrease, e.g., fluid
deprivation or by hypertonic saline solutions)
– Increase in hypothalamic cell dehydration receptor activity
– Increase in supraoptic nucleus activity
– Increase in ADH release from posterior pituitary
– Water reabsorption by kidney
– Or increase in thirst center activity
– Increase in water intake
• Body fluids (extracellular volume) decrease, e.g., decrease in
– Cardiopulmonary stretch receptor activity (low pressure side,
e.g., atria, great veins, pulmonary vessels)
– Increase in sympathetic activity (vasoconstriction)
– Inc in renin- angiotensin II
– Vasoconstriction and decreased excretion of salt and water by
– Angiotensin II also acts on supraoptic nucleus of hypothalamus
(ADH) and thirst center
– Result – increased arterial pressure and fluid volume
Water Balance and Drinking
• Anterior hypothalamus – prevents temperature rise (panting, sweating,
vasodilation) – site of vascular temperature receptors
• Posterior hypothalamus prevents temperature loss - glucose oxidation,
vasoconstriction, piloerection, shivering
• Hypothalamic thermostat – affected by aspirin, alcohol, interleukins
Temperature Regulation
Sleep, Waking, Circadian Rhythm
• The suprachiasmatic nucleus is thought to be the primary “biological
clock” in mammals.
• It works in conjunction with the reticular activating system, and other
brain stem nuclei
Emotional Behavior
• Lesions in the ventromedial hypothalamic nuclei produce savage and
vicious behavior, indicative of extreme rage.
• Stimulation of the dorsomedial nuclei also produces this reaction
Nervous System Effects on Immune Function
Immune system suppression by stress
Via hypothalamo-pituitary-adrenal axis – CRF release
Rats can be conditioned to suppress immune responses
ANS/SNS innervates immune tissues: spleen, lymph nodes, intestinal
Peyer’s patches, bone marrow
• Immune cells have receptors for neurotransmitters
• Different CNS lesions can decrease or increase immune functions.