Hypothalamus – Anatomy, Nuclei and Function | Kenhub

At the core of any well-oiled machine, there is a busy engine that keeps it going. The hypothalamus is at the center of a plethora of physiological processes including, but not limited to, thermoregulation, osmoregulation and hormonal regulation. It also works closely with the pituitary gland to modulate endocrine activity based on the bodys physiological demands.

The purpose of this article will be to evaluate the gross anatomical organization and vascular supply of the hypothalamus. Additionally, the article will look at key anatomical relationships to other structures, some associated neuronal pathways and the function of different nuclei of hupothalamus.

The human hypothalamus and its nuclei

Recommended video: Medial view of the brain

Structures seen on the medial view of the brain. The images show a midsagittal section of the brain.

The left and right lateral walls of the third ventricle are divided by an anteroposterior depression known as the hypothalamic sulcus.

It runs from the anterior tip of the fornix between the interventricular foramen of Monro superiorly and the anterior commissure inferiorly to the posterior commissure (superior to the beginning of the cerebral aqueduct of Sylvius). This depression separates the thalamus (superiorly) from the hypothalamus (inferiorly).

Anterior (preoptic) hypothalamic area

The hypothalamus is composed mainly of different nuclei (discrete masses of grey matter in the central nervous system) that synthesize different hormones in response to physiological changes. These nuclei have been grouped into four regions. The preoptic region (at the level of the subcallosal gyrus) houses the preoptic nucleus. In the supraoptic region, there is the suprachiasmatic, supraoptic, paraventricular, and anterior nuclei. The dorsomedial, ventromedial, arcuate, premammillary and lateral tuberal nuclei belong to the tuberal region. Finally, the mammillary and posterior nuclei are residents of the mammillary region.

Mammillary hypothalamic region

The first of several major hypothalamic nuclei to be discussed is the paraventricular nuclei. It is located anterior to the pathway of the fornix (arching C-shaped collection of nerve fibers) and posteroinferior to the anterior commissure. The superior part of the lamina terminalis is directly anterior to it, while the supraoptic and dorsomedial nuclei are at inferiorly and posteriorly related, respectively.

The supraoptic nucleus is directly posterior to the inferior part of the lamina terminalis and anteroinferior to the dorsomedial and ventromedial nuclei. It also rests directly above the supraoptic crest, also known as the organum vasculosum laminae terminalis (OVLT), just above the supraoptic recess and the optic chiasm.

The arcuate (infundibular) nucleus rests along the proximal part of the tuber cinereum. It is inferior to the ventromedial, anterior to the mammillary, and posteroinferior to the supraoptic nuclei. The dorsomedial and ventromedial nuclei are found around the mid-medial section of the hypothalamus. The former nucleus is located inferiorly to the latter nucleus.

The posterior nucleus is directly superior to the mammillary nucleus, which is found in the mammillary bodies. The posterior nucleus also lies between the fornical nerve fibers (anteriorly) and the mammillothalamic tract (posteriorly).

The hypothalamus has an almost geometrically central location in the brain. As a result, it is structurally related to several other important parts of the forebrain and midbrain.

Internal carotid arteries

Bilateral to the optic chiasm, and inferior to the anterior perforating substance, the left and right cavernous internal carotid arteries each give an anterior cerebral artery and a posterior communicating cerebral artery. The left and right anterior cerebral arteries anastomose along the ventral part of the longitudinal cerebral fissure (near the lamina terminalis) by way of the anterior communicating artery.

The left and right posterior communicating arteries each anastomose with the left and right posterior cerebral arteries (branches of the basilar artery) to unite the vertebral and internal carotid circulatory systems of the brain. The anterior and posterior anastomoses form a circular arterial system known as the cerebral arterial circle of Willis. Anterior and posterior branches of the circle of Willis provide arterial blood to the hypothalamus. The hypothalamus also receives arterial supply from the hypothalamic branches of the superior hypophyseal artery.

The hypothalamic arteries have anastomotic connections to the primary and secondary capillary plexuses of the pituitary gland. The plexuses drain venous blood to the cavernous sinus, which then drains to the superior and inferior petrosal sinuses. The superior petrosal sinus joins the transverse sinus to form the sigmoid sinus. The sigmoid sinus is later joined by the inferior petrosal sinus and becomes the internal jugular vein.

Supraopticohypophyseal tract

Unmyelinated axons of the paraventricular and supraoptic nuclei travel together as the supraopticohypophyseal tract along the anterior region of the hypothalamus caudally, towards the infundibulum (pituitary stalk). They meet up with the axons of the arcuate nucleus that travels along the tuber cinereum (tuberohypophyseal tract) and travels through the infundibular stem of the neurohypophysis to enter the pars nervosa. These two neuronal tracts form the hypothalamohypophyseal tract. It conveys neurons produced in the cell bodies in the hypothalamus to the pars nervosa, where they are stored.

Two sets of nerve bundles travel to the mammillary body. One journeys from the fornix, anterior to the posterior nucleus and the other from the thalamus, posterior to the posterior nucleus. The latter is known as the mammillothalamic tract.

The different nuclei described earlier each have specific functions. Together, they allow the very small hypothalamus to be the regulator of a wide variety of functions.

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Hypothalamus - Anatomy, Nuclei and Function | Kenhub