Chapter 30 – The Hypothalamus

The hypothalamus is a small, anatomical region of the diencephalon that is separated superiorly from the dorsal thalamus by the hypothalamic sulcus. The rostral boundary of the hypothalamus is the lamina terminalis. The lateral boundary of the hypothalamus is formed rostrally by the substantia innominata and caudally by the medial edge of the posterior limb of the internal capsule. Medially, the hypothalamus is bordered by the inferior portion of the third ventricle. Caudally, the hypothalamus is not sharply demarcated, merging instead into the midbrain tegmentum and the periaqueductal gray. Externally, the boundary between the hypothalamus and the midbrain is represented by the caudal edge of the mammillary body. The hypothalamus is involved in the control of visceral functions and emotional behavior. Through influences on the visceromotor center, endocrine system, and limbic system, the hypothalamus partially regulates water and electrolyte balance, food intake, temperature, blood pressure, sleep-waking mechanism, circadian rhythmicity, emergency responses to stressors in the environment, and reproduction through mating and pregnancy.