The Hypothalamus

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Last updated 30 March 2006

The Hypothalamus

Robinson, S. University of NSW, Neuroanatomy (ANAT 2007) tutorial. 1 September 1998.

Click here to go to the Hypothalamus under "The Diencephalon".

General Functions of the Hypothalamus

Hypothalamic neurons measure blood temperature, osmolarity and hormone levels.
The hypothalamus integrates the ANS especially during emotional responses.
It also regulates endocrine functions of the adenohypophysis (anterior pituitary) by releasing neurohormones into the hypophyseal portal system.
It regulates the function of the kidneys, uterus and mammary glands by releasing vasopressin (anti-diuretic hormone, ADH) and oxytocin into the bloodstream.

Borders of the Hypothalamus

Rostral	Lamina terminalis
Caudal	Posterior margin of the mammillary bodies
Dorsal	Hypothalamic sulcus
Medial	3^rd ventricle
Lateral	Subthalamus and internal capsule
Ventral	Optic chiasm, tuber cinereum, mammillary bodies and neurohypophysis (posterior pituitary)

Organisation of the Hypothalamus

Nuclei in the lateral zone initiate eating (hunger centre) and drinking (thirst centre).
Nuclei in the medial zone are subdivided into 3 parts: anterior, tuberal and posterior.

Anterior Nuclear Group

Preoptic nucleus	Controls the parasympathetic nuclei
Supraoptic nucleus	Synthesis and secretion of vasopressin. Lesions of this nucleus can cause diabetes insipidus.
Suprachiasmatic nucleus	Receives retinal input and projects to the pineal gland. This controls circadian rhythms.
Anterior nuclei	Some (esp. INAH3) are larger in male heterosexuals, due to circulating androgens in perinatal life which "rescues" neurons from programmed cell death. It is involved in response to temperature and sexual preference.
Paraventricular nucleus	Synthesis and secretion of oxytocin (milk ejection reflex and uterine contractions). It also regulates food intake.

Tuberal Nuclear Group

Dorsomedial nucleus	Both of these may be involved with the paraventricular nucleus in inhibiting eating and drinking (satiety centre). Lesions of these nuclei can cause eating disorders.
Ventromedial nucleus
Arcuate nucleus	Function is unknown.

Posterior Nuclear Group

Posterior nucleus	Regulates the body's response to cold and controls the sympathetic nervous system.
Mammillary nuclei	They are part of the limbic system. They are prone to damage in chronic alcoholism. Korsakoff's patients have amnesia, but can recall if a hint is provided. This suggests that the mammillary bodies code memories so that they can be retrieved.

Connections

Main Afferent Pathways

The hypothalamus receives afferents from most parts of the brain (including cerebral cortex, reticular formation and solitary nucleus).
Most pathways are unmyelinated and small.

Medial Forebrain Bundle

From the septal area and lateral olfactory area to various hypothalamic nuclei.
It may link olfaction and emotion with feeding.

Stria Terminalis

From the amygdala to septal area, preoptic area and anterior hypothalamic nuclei.
It probably influences physiological responses to emotions and sexual arousal.

Fornix

Main Efferent Pathways

Mammillothalamic Fasciculus

Hypothalamic-Reticular Pathway

This is the 1^st stage in a pathway that links the hypothalamus to the parasympathetic system and sympathetic nuclei of the brain and spinal cord.