Diencephalon: hypothalamus and epithalamus

Hypothalamus The hypothalamus is the region of the mammalian brain that is most important in the coordination of behaviors essential for the maintenance and continuation of the species. Although the hypothalamus occupies only about 0.15% of the volume of the human brain, it plays a major role in the regulation and release of hormones from the pituitary gland, maintenance of body temperature, and organization of goal-seeking behaviors such as feeding, drinking, mating, and aggression. It is the primary center for the control of autonomic function. It is also the region of the brain that is essential for behavioral adjustments to changes in the internal or external environment (Figure 8.1). The hypothalamus is a very old structure with striking similarity between humans and lower animals. It is made up of a number of nuclei and scattered cell groups. Some hypothalamic cell groups control specific functions (e.g., blood pressure, heart rate, etc.) through the coordinated action of short intrahypothalamic connections. Other nuclei operate by projections to structures outside the confines of the hypothalamus. Anatomical and behavioral considerations The hypothalamus lies on either side of the walls of the third ventricle below the level of the hypothalamic sulcus (Figure 8.2, see Figures 9.2, 9.3, and 14.6). It is bounded in front (rostrally) by the lamina terminalis and optic chiasm, laterally by the optic tracts, and behind by the mamillary bodies. Some hypothalamic nuclei are continuous across the floor of the third ventricle.