The Hypothalamus - Parts and Function

Human brain, illustration
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When people talk about the connection between mind and body, they probably don’t usually mean the hypothalamus. Maybe they should.  This small region of the brain is a major nexus between our mind and our heart. 

The part of us we normally think of as “thinking” relies on neocortex, the large expansion of nervous tissue near the brain’s surface.  Control of our heart, blood pressure, and other basic aspects of living lie closer to the brain’s center.

  The hypothalamus gets its name from being below the thalamus near the top of the brainstem.  A narrow stalk juts out from below the hypothalamus, ending in a bulb known as the pituitary gland.   Through the pituitary gland, the hypothalamus regulates several of the hormones that we associate with love, fear, excitement and more. 

Parts of the Hypothalamus

The hypothalamus is made up of several smaller nuclei, each responsible for a slightly different function.  It is useful first to divide the hypothalamus into medial and lateral aspects.  Medial means closer to the brains center, and lateral means closer to the sides of the brain.  The lateral hypothalamic nucleus s very important in appetite.  Animals in which the lateral hypothalamus has been lesioned lose their desire to eat and can become skeletal in appearance. In contrast, when the medial part of the hypothalamus it’s a lesion, animals may become obese and eat uncontrollably.

The medial aspect of the hypothalamus is itself divided into several sub-nuclei Some of  the most anterior (close to the front of the brain) regions of the hypothalamus include the superoptic and paraventricular nuclei which  produce the hormones oxytocin and vasopressin, both involved with feeling attachment.

  This area of the hypothalamus also includes the suprachiasmatic nucleus. This nucleus is the master clock for circadian rhythms—how our body knows when it’s time to wake up and when it’s time to fall asleep. The suprachiasmatic nucleus receives input from retinal ganglion cells in  the eye too adjust for day and night cycles.

The arcuate nucleus is a little further back, and helps to control the anterior pituitary gland.  Hormones in the anterior pituitary gland include the following:

  • Adrenocorticotropic hormone (ACTH):  stimulates adrenal cortex to make corticosteroid hormones, e.g. cortisol, and also aldosterone (a mineralocorticoid), which maintain blood pressure, control electrolyte balance, promote glucose mobilization, and more.
  • Thyroid stimulating hormone (TSH): stimulates the thyroid gland to produce thyroxine (T4) and triiodothyronine (T3) which promote cellular metabolism
  • Growth hormone (GH) – causes liver, kidneys and other organs to produce somatomedins or insulin like growth factors.
  • Prolactin – Stimulates the mamillary glands to produce milk
  • Luteinizing hormone and follicle stimulating hormone- regulate ovarian hormones for the menstrual cycle and oogenesis in females, and testicular hormones and spermatogenesis in males.

Regions near the back of the hypothalamus have an important role in conserving heat.  Without this region, we would essentially be cold blooded as lizards or fish.  The anterior hypothalamus is more involved with shedding heat—people with lesions in this region may develop a bad fever.

The Brain Body Connection

Many nuclei of the hypothalamus, such as the paraventricular, dorsomedial, lateral and posterior, help to control the autonomic nervous system, which is responsible for controlling heart rate, sweating, blood pressure and other aspects of life sensibly placed largely beyond our conscious control.  That doesn’t mean we can’t change these things consciously, however.  The amygdala and anterior cingulate gyrus are a major interfaces between the hypothalamus and neocortex.   These regions are also critical for emotion, which is why we might be able to make our hearts speed up by thinking about someone we love, for example. 

Sources: 

Hal Blumenfeld, Neuroanatomy through Clinical Cases. Sunderland: Sinauer Associates Publishers 2002

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