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Where Is The Hypothalamus Located In The Brain

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Iiibthe Hypothalamus And Sleep

The Hypothalamus: Rapid Review

Importantly, neurochemical lesions of VLPO and surrounding neurons have revealed greater functional parcellation of the anterior hypothalamic circuitry involved in sleep regulation. Cell-selective lesions that do not interrupt fibers of passage were shown to compromise different aspects of sleep based on the localization of the lesion. Lesions confined to the compact portion of VLPO dramatically reduce non-REM sleep and, in circumstances in which lesions are incomplete, the amount of non-REM sleep is linearly correlated with the number of Fos-expressing neurons in the portion of the VLPO that survived the lesion. Interestingly, lesions dorsal to VLPO that eliminate galanin-containing neurons that project to TM produce sleep deficits more closely associated with REM than with non-REM sleep. Collectively, these observations provide compelling evidence in support of a prominent role for the hypothalamus in sleep regulation and further indicate that there is functional parcellation in the neurons of the VLPO that participate in this control.

Luis Puelles, … J.L.R. Rubenstein, in, 2012

Keeping Hypothalamic Hormones In Balance

Anti-Diuretic Hormone

Anti-Diuretic Hormone is controlled by a negative feedback loop. The hypothalamus increases ADH when there is too much salt or electrolytes in the blood, or when blood pressure or volume falls. When the hypothalamus senses that salt concentrations and blood pressure have returned to normal, it makes less ADH.

Oxytocin

Oxytocin is controlled through a positive feedback loop. Oxytocin starts to be made when nerves leading to the hypothalamus are activated. This occurs when a baby starts to suckle at the breast. As the baby feeds, the nerves in the breast signal to the hypothalamus to release oxytocin. More and more oxytocin is released until the nerves stop signalling when the baby finishes feeding.

Corticotrophin Releasing Hormone

Corticotrophin Releasing Hormone is controlled through a negative feedback loop. CRH from the hypothalamus signals the pituitary gland to make adrenocorticotrophic hormone . ACTH then signals the adrenal glands to make glucocorticoid hormones. The major glucocorticoid hormone is cortisol. This system is called the hypothalamic pituitary adrenal axis . Cortisol travels through the blood and is recognised by the hypothalamus and pituitary gland. When a threshold is reached, cortisol signals to the hypothalamus and pituitary to make less CRH and ACTH. The HPA axis is the main system that is activated in response to stress.

Thyrotrophin Releasing Hormone
Gonadotrophin Releasing Hormone

What Is The Hypothalamus And What Does It Do

The hypothalamus is a collection of nuclei with a variety of functions. Many of the important roles of the hypothalamus involve what are known as the two H’s: Homeostasis and Hormones.

Homeostasis is the maintenance of equilibrium in a system like the human body. Optimal biological function is facilitated by keeping things such as body temperature, blood pressure, and caloric intake/expenditure at a fairly constant level. The hypothalamus receives a steady stream of information about these types of factors. When it recognizes an unanticipated imbalance, it enacts a mechanism to rectify that disparity.

The hypothalamus generally restores homeostasis through two mechanisms. First, it has connections to the autonomic nervous system, through which it can send signals to influence things like heart rate, digestion, and perspiration. For example, if the hypothalamus senses that body temperature is too high, it may send a message to sweat glands to cause perspiration, which acts to cool the body down.

The hypothalamus thus has widespread effects on the body and behavior, which stem from its role in maintaining homeostasis and its stimulation of hormone release. It is often said that the hypothalamus is responsible for the four Fs: fighting, fleeing, feeding, and fornication. Clearly, due to the frequency and significance of these behaviors, the hypothalamus is extremely important in everyday life.

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Diet Tips For Hypothalamus Health

As the hypothalamus plays such a vital role in the body, it is very important to keep it healthy. While a person cannot fully avoid genetic factors, they can take dietary steps towards ideal hypothalamus health on a daily basis to reduce the risk of hypothalamic disease.

The hypothalamus controls the appetite, and the foods in the diet influence the hypothalamus. Studies have shown that diets high in saturated fats can alter the way the hypothalamus regulates hunger and energy expenditure.

Connections With The Pituitary Glandpituitary Glandthe Pituitary Gland Also Known As The Hypophysis Is Considered The Master Endocrine Gland Because It Releases Hormones That Regulate The Activity Of Multiple Major Endocrine Organs In The Body The Gland Sits On The Sella Turcica Just Below The Hypothalamus Which Is The Primary Regulator Of The Pituitary Gland Pituitary Gland

Hypothalamus

The hypothalamus is the primary regulator of the pituitary. The hypothalamus is therefore key in converting and integrating nerve signals with endocrine signals. The hypothalamus is connected to the pituitary in 2 ways: via nerve fibers and via the circulation.

Nerve fiber connections: the hypothalamohypophysial tract

  • Neurons in the paraventricular and supraoptic nuclei have direct projections that end in the posterior pituitary.
  • Secretions include:
  • Paraventricular nuclei: primarily produce oxytocin
  • Supraoptic nuclei: primarily produce antidiuretic hormone

Diagram of the nervous connections between the hypothalamus and the posterior pituitary glandPituitary glandThe pituitary gland, also known as the hypophysis, is considered the “master endocrine gland” because it releases hormones that regulate the activity of multiple major endocrine organs in the body. The gland sits on the sella turcica, just below the hypothalamus, which is the primary regulator of the pituitary gland. Pituitary Gland:

Bloodstream connections: the hypothalamohypophysial portal system

  • Dopamine
  • Diagram of the hypothalamohypophysial portal system connecting the hypothalamus and the anterior pituitary

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    Control Centres For Making Sense Of Our Bodies

    Apart from the cerebrum, the forebrain also contains several small, but highly important structures located towards the centre of the brain and are included in the limbic system. Collectively these are called the diencephalon and they are involved in regulating things like the bodys sensory perception, motor functions, and hormones.

    The thalamus consists of two lobes of grey matter tucked away right under the cerebral cortex. It is a prime processing centre for sensory information, as it links up the relevant parts of the cerebral cortex with the spinal cord and other areas of the brain important for our senses. The thalamus also controls sleep.

    The hypothalamus is quite small, only about the size of an almond. As its name suggests, it can be found right underneath the thalamus, and despite its small size it is actually the major control centre of the autonomic motor system. It is involved in some hormonal activity and connects the hormonal and nervous systems. The hypothalamus also works to regulate things like our blood pressure, body temperature, and overall homeostasis.

    The pineal gland is even smaller than the hypothalamus – only about the length of a grain of rice – and is tucked between the two lobes of the thalamus. It is actually shaped like a tiny pinecone, and its main job is to produce the hormone melatonin, which regulates our sleep-wake cycles. Just like the hypothalamus, it is also involved in regulating hormonal functions.

    Embryological Development Of The Hypothalamus

    At the end of the fourth week of embryological development, the neural tube is organized in primary vesicles: the forebrain vesicle or prosencephalon, the midbrain vesicle or mesencephalon, and the hindbrain vesicle, also called rhombencephalon. Prosencephalon further divides into two secondary vesicles, the telencephalon that will form the cerebral hemispheres and the diencephalon which gives rise to the diencephalon. Mesencephalon forms the midbrain, structure involved in the processes of vision and hearing. The hindbrain vesicle or rhombencephalon divides in metencephalon, which further forms the pons and the cerebellum and the myelencephalon that forms the medulla.

    Embryological concepts regarding the development of the hypothalamic region are over 100 years old. Since Herrick first proposed the columnar model of the forebrain organization, the anatomical description was accepted per se and very few research papers have questioned its validity.

    The columnar morphologic model is based on the division of the forebrain in functional longitudinal units, placing the telencephalon in the most rostral region and the diencephalon caudally, in between the telencephalon and the midbrain, while the hypothalamus if formed from the ventral most part of the diencephalic vesicle .

    An important role in hypothalamic development is assigned also to the presence of specific signaling centers that modulates cell proliferation and neurulation .

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    The Hypothalamus And Adenohypophysis

    The hypothalamus is the source of TRH released from the median eminence and travels to the pituitary thyrotrope via the hypothalamushypophysial portal system. TSH release is stimulated by TRH, which in turn produces an increase in circulating thyroid hormones. Synthesis and release of TSH are regulated through an IP3 second-messenger system . Calcium ions also are involved in release of TSH from the thyrotrope. Sensitivity of the thyrotrope to TRH may be affected by paracrines secreted from other pituitary cells.

    The increase in the cellular portion of the follicle due to hypertrophy and concomitant reduction in colloid are reflected in a change in the diameter of the follicle with respect to the thickness of the epithelium and/or volume of the lumen. The ratio of follicle diameter to thickness of the epithelium or diameter of the follicular lumen changes predictably with TSH levels and frequently has been used as a measure of the degree of stimulation by TSH. Generally, a stimulated histology is indicative of thyroid hormone deficiencies and enhanced TSH secretion to compensate for these deficiencies. Other factors such as cold stress, however, may be operating at the hypothalamus to elevate TSH secretion above that normally maintained through negative feedback by thyroid hormones. This effect also may cause follicular cell hypertrophy.

    Potential Problems With The Hypothalamus

    How the Brain Works: Hypothalamus

    Just like any other part of the body, there are potential diseases and injuries that could particularly affect the hypothalamus. The difficulty with hypothalamic injuries and diseases is that, because the hypothalamic is so far-reaching in its roles in the central nervous system, limbic system, and endocrine system, it can pose a tremendous challenge to diagnose and treat issues that may arise in connection to this organ.

    One of the most well-known problems affecting the hypothalamus is hypothalamic disease .

    Hypothalamic disease is most commonly caused by physical trauma to the head and can span over a number of disorders or hypothalamus-related malfunctions. Symptoms can manifest as sleeping disorders, problems with appetite, growth abnormalities, and more.

    Other causes include surgery, radiation, and tumors. There are even genetic links to hypothalamic diseases like Kallman and Prader-Will syndromes, for example. Diabetes insipidus and hypopituitarism are other known disorders related to the malfunctioning of the hypothalamus.

    When symptoms are too difficult to decipher or multiple symptoms occur at once, the issue may be referred to as a hypothalamic-pituitary disorder. This is because the hypothalamus and pituitary gland work so closely together. But dont worry! Its not all a guessing game. There are tests to monitor hormone levels that narrow down the possibilities as to what may be the source of the disorder or disease.

    References

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    Nuclei Of The Hypothalamus

    As mentioned above, the hypothalamus actually consists of a collection of nuclei, each of which have their own functional roles in the brain. In this section, I will briefly discuss the main hypothalamic nuclei and summarize some of their functions. It’s important to note that this will not be a complete list of all of the nuclei in the hypothalamus, nor a thorough explanation of everything those nuclei are involved in . Also, some hypothalamic nuclei are subdivided into smaller nuclei I will not go into that level of detail in this section. Finally, it’s important to mention that the nuclei of the hypothalamus are paired structures, meaning there is one nucleus on either side of the midline of the hypothalamus. So, while below I will discuss individual nuclei such as the suprachiasmatic nucleus, this would be more accurately described as the suprachiasmatic nuclei because there are two of them.

    The anterior hypothalamus contains a region called the preoptic area, which contains several preoptic nuclei. Different nuclei of the preoptic area are involved in: the regulation of blood composition and volume , the regulation of body temperature, sleep regulation, and reproductive behavior. You can read more about the preoptic area in this article: Know Your Brain: Preoptic Area.

    The anterior nucleus is situated above the supraoptic nucleus it is best-known for its role in the regulation of body temperature.

    Efferent Nerve Connections Of The Hypothalamus

    The hypothalamus sends efferent signals to:

    • Descending fibers in the brain stemBrain StemThe brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle.Brain Stem and spinal cordSpinal cordThe spinal cord is the major conduction pathway connecting the brain to the body it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter and a surrounding area of white matter . Spinal Cord affect peripheral autonomic nervous systemAutonomic nervous systemThe ANS is a component of the peripheral nervous system that uses both afferent and efferent neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ANS consists of the sympathetic and parasympathetic nervous systems. Autonomic Nervous System:
    • Sympathetic preganglionic neurons
  • Mammillothalamic tract: mammillary body thalamus
  • Limbic systemLimbic systemThe limbic system is a neuronal network that mediates emotion and motivation, while also playing a role in learning and memory. The extended neural network is vital to numerous basic psychological functions and plays an invaluable role in processing and responding to environmental stimuli.Limbic System
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    The Hypothalamus Pituitary And Pineal Glands

    Three glands of critical importance to the body, the hypothalamus, pituitary and pineal glands, are all located in the brain.

    These glands work synergistically to control many functions in the body.

    Many children today experience symptoms because their hormones are out-of-balance or out-of-sync with one another.

    Hormones have their individual functions, but they may not be able to do their jobs if they are not in balance or in sync with other hormones in the body.

    Any hormone out-of-sync disrupts all the other hormones and their functioning.

    Hormones are very complex and sensitive to diet and toxins.

    Lets look at each of these important glands.

    Function Of The Hypothalamus

    Hypothalamus: Function, hormones, and disorders

    The function of the hypothalamus is to help regulate your body’s processes and to release hormones. The hormones it makes travel to the anterior pituitary through the blood.

    The hypothalamus can make the following hormones:

    • Dopamine: A brain chemical that influences mood and feelings of reward and motivation
    • Somatostatin: Regulates the gastrointestinal tract and other important bodily functions
    • Oxytocin: Fosters positive feelings of connection and well-being, sometimes called the love hormone
    • Vasopressin: An antidiuretic hormone involved in regulating fluid levels in the body
    • Growth hormone-releasing hormone : Stimulates the release of growth hormone
    • Thyrotropin-releasing hormone : Regulates the release of an important thyroid hormone.
    • Gonadotropin-releasing hormone : Stimulates the production of testosterone
    • Corticotropin-releasing hormone : Helps drive the body’s stress response

    Some of the functions of the hypothalamus include regulating:

    • Hunger and appetite
    • Brain MRI and CT scans

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    Causes And Risk Factors

    The most common causes of hypothalamic diseases are injuries to the head that impact the hypothalamus. Surgeries, radiation, and tumors can also cause disease in the hypothalamus.

    Some hypothalamic diseases have a genetic link to hypothalamic disease. For instance, Kallman syndrome causes hypothalamic problems in children, most noticeably delayed or absent puberty, accompanied by an impaired sense of smell.

    Hypothalamus problems also appear to have a genetic link in Prader-Willi Syndrome. This is a condition in which a missing chromosome leads to short stature and hypothalamic dysfunction.

    Additional causes of hypothalamic disease can include:

    • eating disorders, such as bulimia or anorexia
    • genetic disorders that cause excess iron buildup in the body

    What Does Your Hypothalamus Do

    Your hypothalamus receives chemical messages from nerve cells in your brain and from nerve cells in your body , which is also responding to signals outside your body.

    Your hypothalamuss main function is to react to these messages to keep your body in a stable state or internal balance. Just like you may have a smart control system to seamlessly manage all functions in your home, your hypothalamus is your bodys smart control coordinating center. Your hypothalamus helps manage your:

    Your hypothalamus performs many of its body balancing jobs either by directly influencing the autonomic nervous system or by managing hormones. Your autonomic nervous system control several important functions, such as your heart rate and breathing .

    Hormones are the chemical messengers that travel in your bloodstream to another part of your body. Hormones communicate either with another endocrine gland or with a specific organ.

    Your hypothalamus:

    • Makes some hormones itself that are stored elsewhere .
    • Sends signals to your pituitary gland, which either releases hormones that directly affect a part of your body or sends another signal to a different gland in your body that then releases its hormone.

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    Regulation Of Food Intake

    The hypothalamus controls appetite and food intake through the ventromedial, dorsomedial, paraventricular, and lateral hypothalamus nucleus. The ventromedial nucleus is referred to as the appetite-suppressing or anorexigenic center. Destruction of this nucleus leads to hyperpolyphagia, obesity, and to an aggressive behavior.

    Contrary, the appetite-increasing or orexigenic center is considered to be the lateral hypothalamic nucleus that can lead to aphagia and cashexy in case of its destruction and to hyperphagia or polyphagia in case of its stimulation.

    Appetite control is modulated by the leptin hormone released by the fatty cells that binds to specific hypothalamic receptors.

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