Hypothalamus

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*Overall information:

-The hypothalamus is located deep inside the brain, below the thalamus and above the pituitary gland. It is a part of the diencephalon (cluster of grey matter deep within the cerebrum)

-The hypothalamus has a role in the autonomic nervous system (work with the sympathetic nervous system to speed up activity or parasympathetic to slow down activity). It also communicates with the endocrine system for hormone production. Additionally, it is an indispensable part of the limbic system (emotion, memory, learning, behavior) 

*Nuclei inside the hypothalamus:

1. Preoptic zone: contains medial preoptic nucleus.
2. Supraoptic zone: contains supra chiasmatic nucleus, supra optic nucleus, paraventricular nucleus, anterior hypothalamic nucleus. 
3. Tuberal zone: contains arcuate nucleus, ventral medial nucleus, dorsal medial nucleus. 
4. Mammillary zone: contains mammillary nucleus, posterior hypothalamic nucleus. 

*Functions of the hypothalamus:

-Limbic system 

+Memory and learning:

• The hypothalamus is involved in the papez circuit which activates the memory and learning activities. 

+Emotional and behavioral (feeding, sexual, motivation) response:

• The amygdala (an important structure in the limbic system) receives information from the posterior association cortex and sends them to the hypothalamus for emotional and behavioral expression. 
• The amygdala also communicates with the hypothalamus for feeding purpose or sexual drive. 

-Endocrine system:

+Arcuate nucleus is the site of releasing and inhibiting hormones. It releases some specific hormones into the hypothalamic hypophyseal portal system (a portal circulation) which connects the hypothalamus to the anterior pituitary.

• Growth hormone releasing and inhibiting hormones will activate or inactivate the pituitary cell to release growth hormone for muscle and bone growth.
• Corticotropin releasing and inhibiting hormones will activate or inactivate the anterior pituitary cell to release ACTH  which stimulates the adrenal cortex to release cortisol (controls blood sugar level, regulates metabolism,…)
• Prolactin inhibiting hormone will regulate the activity of the cell body inside the anterior pituitary to release prolactin hormone which later acts on the mammary gland (milk production).
• Thyrotropin releasing and inhibiting hormones stimulate the production of thyroid hormone (controls heart, muscle, digest functions, brain development, and bone maintenance).

+Medial Preoptic nucleus releases gonadotropin releasing and inhibiting hormones which stimulate the production of FSH (follicle stimulating) and LH (luteinizing) inside the anterior pituitary cell. These outcomes help drive the reproductive system. 

+If we have low water balance, the supraoptic nucleus will release a specific type of hormone inside the posterior pituitary which acts on the blood vessels and the kidneys to increase the blood pressure and volume for water balance inside our body. 

+Baby suckling or uterine stretch will stimulate the paraventricular nucleus to release oxytocin which then acts on the uterus to increase uterine contraction or acts on the milk glands for milk production. 

-Autonomic nervous system:

+Anterior hypothalamic nucleus and posterior hypothalamic nucleus are involved in parasympathetic and sympathetic nervous systems respectively. 

• Fibers which originate from the anterior hypothalamic nucleus will come down to the spinal cord (dorsal longitudinal fasciculus) and innervate cranial nerves 3, 7, 9, and 10.
• Sympathetic fibers coming from the posterior hypothalamic nucleus will come down to the spinal cord (hypothalamus spinal tract) and stimulate the nerves that are used for sympathetic activities. 

+Anterior and posterior hypothalamic nucleus are also involved in thermoregulation. 

• Anterior hypothalamic nucleus causes vasodilation of the cutaneous vessels (vessels near the skin) and sweating to decrease body temperature. 
• Posterior hypothalamic nucleus causes vasoconstriction of the cutaneous vessels and shivering to increase body temperature.