Hypothalamus:

the hypothalamus is colored green in the image above.

the hypothalamus is colored green in the image above.

group of nuclei that lies just below the thalamus. The hypothalamus is crucial in the maintenance of homeostasis, as well as reproductive functions, fight-or-flight reactions, feeding, and sleep.

Further reading: Know your brain: Hypothalamus

Watch these 2-minute videos to learn more:

2-Minute Neuroscience: Hypothalamus & Pituitary Gland

2-Minute Neuroscience: HPA Axis