Hypothalamus - Structure and Inputs

Structure and Inputs

The hypothalamus is a brain structure composed of distinct nuclei and less anatomically distinct areas. It is found in all vertebrate nervous systems. In mammals, the axons of magnocellular neurosecretory cells of the paraventricular nucleus and the supraoptic nucleus, which contain oxytocin and vasopressin (also called antidiuretic hormone), comprise the posterior pituitary. Parvocellular neurons of the paraventricular nucleus contain neurons that release corticotropin-releasing hormone and other hormones into the hypophyseal portal system where these hormones diffuse to the anterior pituitary.

The hypothalamus coordinates many hormonal and behavioural circadian rhythms, complex patterns of neuroendocrine outputs, complex homeostatic mechanisms, and important behaviours. The hypothalamus must therefore respond to many different signals, some of which are generated externally and some internally. The hypothalamus is thus richly connected with many parts of the central nervous system, including the brainstem reticular formation and autonomic zones, the limbic forebrain (particularly the amygdala, septum, diagonal band of Broca, and the olfactory bulbs, and the cerebral cortex).

The hypothalamus is responsive to:

• Light: daylength and photoperiod for regulating circadian and seasonal rhythms
• Olfactory stimuli, including pheromones
• Steroids, including gonadal steroids and corticosteroids
• Neurally transmitted information arising in particular from the heart, the stomach, and the reproductive tract
• Autonomic inputs
• Blood-borne stimuli, including leptin, ghrelin, angiotensin, insulin, pituitary hormones, cytokines, plasma concentrations of glucose and osmolarity etc.
• Stress
• Invading microorganisms by increasing body temperature, resetting the body's thermostat upward.