Hypothalamus: Anatomy & Physiology
Hypothalamic zones
- The medial zone subdivides into periventricular and intermediate zones; they are are highly cellular.
- The lateral zone comprises a high degree of white matter fibers.
The column of the fornix separates the intermediate and lateral zones.
The hypothalamic nuclear groups
The anterior (aka chiasmatic) group
Encompasses the region above and anterior to the optic chiasm and optic tract.
- Suprachiasmatic nucleus
- Anterior nucleus
- Paraventricular nucleus
The middle (aka tuberal) group
Encompasses the region between the optic chiasm and mammillary bodies (ie, the region above the tuber cinereum) * Infundibular (aka arcuate) nucleus
- Ventromedial nucleus
- Dorsomedial nucleus)
Posterior (aka mammillary) group
- Posterior nucleus
- Mammillary bodies (which comprise the medial and lateral mammillary nuclei).
Preoptic region
Preoptic region develops as part of the telencephalon but functions along with the hypothalamus (so it's addressed here).
- Preoptic nuclei (medial and lateral).
Additional hypothalamic nuclei
- Supraoptic nucleus lies above the optic tract, show the – (texts variably list this nucleus as lying within the medially instead of laterally).
- The tuberomammillary nucleus extends through the inferior aspect of the middle (tuberal) and posterior (mammillary) groups.
- The lateral tuberal nucleus is a small nucleus in the posterior aspect of the tuberal region.
Lateral hypothalamic area
- Spans from the posterior optic chiasm to the posterior end of the hypothalamus; it, most notably, contains the medial forebrain bundle.
Hypothalamic Physiology: Simple Rule
Although it is an oversimplification...
- The anteromedial hypothalamus produces parasympathetic activity (eg, satiety, sleep, and heat dissipation to decrease body temperature).
- The posterolateral hypothalamus produces sympathetic activity (hunger, wakefulness, and heat conservation to increase body temperature).
Hypothalamic pathways
Divides into:
- The neurohypophysis, posteriorly.
- Via the hypothalamohypophysial tract, it's responsible for release of:
- Vasopressin & Oxytocin
The adenohypophysis, anteriorly.
Via the hypothalamohypophysial portal venous system, it's responsible for release of several hormones:
- FSH, LH, ACTH, TSH, Prolactin, and Growth Hormone (which are remembered with the acronym FLATPG)
hypothalamohypophysial tract
- Magnocellular neurons of the paraventricular and supraoptic nuclei project via the infundibulum to the primary capillary plexus of the neurohypophysis via the hypothalamohypophysial tract and the neurohypophysis releases hormones into the general circulation via the hypophysial veins.
hypothalamohypophysial portal venous system
- Hypothalamic neurons release hypothalamic hormones into the primary capillary plexus of the median eminence of the hypothalamus, which connects with the secondary capillary plexus of the adenohypophysis via the hypothalamohypophysial portal venous system, and the adenohypophysis endocrine cells release FLATPG hormones into general circulation via hypophysial veins.
Additional key hypothalamic pathways
- Via the medial forebrain bundle, diffuse limbic nuclei (septal, olfactory, periamygdaloid) project through the lateral hypothalamus to the midbrain tegmentum.
- Similar to the median forebrain bundle, the dorsal longitudinal fasciculus projects through the hypothalamus into the brainstem; it coalesces most prominently in the periaqueductal gray area (in the midbrain).
- Via the mammillotegmental fasciculus, mammillary nuclei project to the brainstem tegmentum (most likely the midbrain, but also, possibly, to the pons).
- The medial zone is sometimes used to interchangeably with the intermediate zone instead of comprising both the periventricular and intermediate zones.
- Texts variably list the supraoptic nucleus as lying within the medial hypothalamus, instead of the lateral hypothalamus.