The hypothalamus is the portion of the diencephalon that forms the walls and floor of the third ventricle. Located at the base of the brain, it lies below the thalamus and medial to the internal capsule. The hypophysis is suspended from it by a stalk-like structure. The main function of the hypothalamus is to regulate autonomic, endocrine, metabolic, and somatic motor responses. It is the part of the brain most closely related to the control of the autonomic nervous system. Thus, it regulates the activity of the digestive, cardiovascular, endocrine, and other physiological systems.
Anatomical Description
In humans, the hypothalamus weighs between 4 and 5 grams. It is a mosaic of several small nuclei, which can be distinguished on the basis of their cytoarchitectonics, connections, and cytochemistry. These grey nuclei are embedded in the walls of the third ventricle as widely-scattered masses of neurons working together in a complex network. The hypothalamus contains more than 30 paired clusters of nerve cells. These conglomerates of nerve cells is separated from the thalamus by the hypothalamic sulcus that lies immediately above.
The hypothalamus is composed of an anterior (supraoptic), a lateral, a posterior (mammillary), and an intermediate hypothalamic area. Each of these areas contains specific nuclei. It has efferent and afferent fiber connections with the lymbic system, mesencephalon (midbrain), cerebrum, and cerebellum. It also has functional connections with the anterior lobe of the hypophysis (pituitary gland) as its parvocellular neurosecretory cells secretes regulatory hormones that regulate the endocrine cells of the hypophysis. These releasing and inhibiting hormones are carried from the hypothalamic nuclei to the anterior lobe of pituitary gland through the hypophyseal portal system, which is the vascular system that joins both structures.
Below, an schematic picture of the hypothalamus, showing its efferent connections with different areas of the brain.
Below, the afferent connections of this brain structure.
