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PostPosted: Fri Jun 07, 2013 11:37 pm 
Broken Crown Panelist
Broken Crown Panelist

Joined: Thu Nov 15, 2012 5:09 pm
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Before starting in on this month's topic - I'd like to call your attention to Stephen Euin Cobb's "The Future and You" podcasts. Stephen takes on many topics of science and speculation to look at how you can affect the future, and how the future will affect you. Last month, Stephen cited an outdated theory of memory and was chastised by a listener - so to remedy the situation, he interviewed a scientist working in the field of memory... yours truly.

So, surf on over to The Future and You to listen to Part 1 of our conversation at:
http://thefutureandyou.libsyn.com/the-future-and-you-may-29-2013

...and now, back to our regularly scheduled blog...

Hypothalamus – When, Where, & How

One of the characteristics of many neurons in the hypothalamus is that instead of releasing their neurotransmitters directly onto other neurons, they release into the blood. At this stage, the chemicals are termed "neuromodulators" because they act to alter neuron activity, instead of directly causing inhibition or excitation of a neuron. The more familiar name is "hormone. The blob hanging down from the middle of the hypothalamus above is the pituitary gland. It is most familiar for its role in promoting adrenaline release from the adrenals glands sitting on top of the kidneys. However, it has other functions as well, as will be detailed below.

The position of the hypothalamus is ideal for collecting signals from various brain areas and sending hormones and releasing factors to the common release site – the Pituitary Gland. The Pituitary has a lot of blood vessels, and thus hormones can be released directly into the blood stream and affect the entire body.

Image
Copyright 2013, Alila Medical Images. Royalty-free image used under license from Shutterstock.

The diagram above shows a "slightly" expanded illustration of the different nuclei of the hypothalamus. The hypothalamus lies under the thalamus (hence the name). It also lies just forward of thalamus and brainstem and in the center of the brain - compared to the thalamus that forms the base of the two lateral hemispheres of the brain. This is not to say that the hypothalamus doesn't have right/left divisions. The picture below shows the same structures from a slice of brain that is essentially a 90 degree rotated angle.

Image
Copyright 2013, Alila Medical Images. Royalty-free image used under license from Shutterstock.

The regions of the hypothalamus, as well as their functions include:

Anterior Medial (front, center) Region:
    Medial Preoptic nucleus - which controls urinary bladder pressure and decreases heart rate and blood pressure
    Supraoptic nucleus (located just over the optic nerve) - which releases oxytocin (uterine contraction) and vasopressin (blood pressure).
    Paraventricular ("between the ventricles") nucleus - which releases oxytocin, vasopressin and corticotropin releasing hormone (CRH, ultimately responsible for triggering the adrenal cortex to release cortisone/cortisol).
    Anterior hypothalamic nucleus - which controls panting, sweating, internal temperature regulation and release thyrotropin (regulates the thyroid).
    Suprachiasmatic (literally "Over the 'X'" referring to the crossover point of the optic nerve) nucleus - which releases vasopressin and regulates circadian rhythm (day/night, sleep/wake cycle)

Anterior Lateral (front, sides) Region
    Lateral portions of preoptic and supraoptic nuclei
    Lateral nucleus - which regulates thirst and hunger (via secretion of a hormane called Orexin or Hypocretin, which is also shown to affect wakefulness)
    Tuberal Region - literally, over the "tube" (pituitary)
    Dorsomedial Hypothalamic Nucleus - which regulates blood pressure and heart rate, as well as stimulating contractions in the intestines
    Ventromedial Nucleus - which regulates satiety (Orexin again, plus another hormone known as Gallanin), and control of neuroendocrine glands (such as thyroid, pancreas, ovaries, testes and adrenals)
    Arcuate Nucleus - which releases Gonadotropin-releasing hormone (GRH, aka Luteinizing hormone releasing hormone, LHRH) to regulate ovaries, releases dopamine (to alter prolactin release from pituitary and regulate lactation), and regulates feeding behaviors - largely in the form of altering taste to seek out essential nutrients.

Posterior Medial (back, center) Region
    Mammillary nuclei - part of the Mammillary Bodies (named for their shape, not their function) - This is actually one end of the Limbic System, and is involved in memory.
    Posterior Nucleus - involved in the release of norepinephrine, a neurotransmitter similar to adrenaline, this area regulates blood pressure (causes arterial contraction), pupil dilation and shivering.
    Posterior Lateral (back, sides) Region
    Lateral Nucleus - actually a continuation of the Anterior Lateral Nucleus

Here's a more detailed look at the Hypothalamus from famed medical illustrator Frank Netter. These beautiful plates originated in 1936 when Netter was commissioned by the CIBA Pharmaceutical Company to illustrate the heart as part of heart medicine advertisements. Netter's Atlas of Human Anatomy was first published in 1989 and is still a favorite among students and professors alike.

Image
Copyright 1989, Elsevier Medical Publishing.

While we're talking about this area of the brain, it's a good idea to include the Pituitary. While technically a gland, and therefore not a nucleus of the hypothalamus, the pituitary (or "Hypophysis" in Neurogeek-speak) is the site at which many of the neuromodulators produced in hypothalamus get into the blood. There are two divisions - Anterior, also known as "Adenohypophysis" (named for its effect on glands) makes and secretes:
    Adrenocorticotropic Hormone (ACTH) which stimulates the adrenal gland. ACTH release is stimulated by CRH from the Paraventricular Nucleus)
    Thyroid-Stimulating Hormone
    Growth Hormone
    Prolactin (regulates mammary milk production and ovaries/uterus)
    Luteinizing Hormone (in women) / Interstitial Cell Stimulating Hormone (men) which regulates ovaries/testes
    Follicle Stimulating Hormone which stimulate ova release from ovaries
    melanocyte stimulating hormone which leads to melanin (skin pigment) formation

The Posterior pituitary stores and releases oxytocin (responsible for labor during pregnancy) and vasopressin. The latter, also known as "Antidiuretic Hormone" regulates blood pressure directly through action on the muscle that line the arteries, but also by regulating water retention in the kidneys.

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So, that's a lot of functions. If the Pre-motor area is the main controller for the muscles of the body, the hypothalamus is the controller for all of the chemically-based signals. Hypothalamus is part of the "diencephalon" which is essentially the core of the brain, and is one of the structures most necessary for most of what we think of as the essential functions of the brain apart from conscious thought.

Not bad for something about the size of a walnut. Kind of makes you rethink those prejudices against dinosaurs, right?

Join us next month for Hypothalamus SSI – The Self-Healing Ability.


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