Located just behind and between the eyes, the anterior border of the hypothalamus is formed by the optic chiasm. It is bordered laterally by the optic tracts and temporal lobes, and the posterior limit of the hypothalamus, occupied by the mammillary bodies, is bounded by the cerebral peduncles.
The hypothalamus, literally located below the thalamus , is divided in the midline by the third ventricle. It contains a series of reasonably well differentiated cell groups or nuclei, sandwiched between to major axonal pathways that connect it with the rest of the brain and with the endocrine system.
The periventricular axon system occupies the medial wall of the hypothalamus along the third ventricle, medial to most of the hypothalamic nuclei. It contains axons that connect the hypothalamus with the brainstem and thalamus.
Some periventricular axons, from neurons that produce pituitary releasing hormones, travel to the median eminence, which is a vascular area in the floor of the third ventricle. Here they secrete the releasing hormones into the portal capillaries, which carry them to the anterior pituitary gland where they control secretion of prolactin, thyrotropin, corticotropin, growth hormone, gonadotropic hormones, and prolactin. Other periventricular axons, from cells in the supraoptic and paraventricular nuclei that produce oxytocin or vasopressin, pass directly through the pituitary stalk to the posterior pituitary gland, where their terminals secrete these hormones into the general circulation.
Many of the neurons that produce releasing hormones are scattered along the wall of the third ventricle, mixed in with the periventricular system.
However, at the base of the third ventricle there is a particularly large collection of such neurons, called the arcuate nucleus, and along the dorsal third ventricle is another such cluster in the paraventricular nucleus.
The lateral hypothalamic axon system , sometimes called the medial forebrain bundle , runs from rostral to caudal through the lateral hypothalamic area, serving to connect the more medial nuclei with the forebrain above, and with the brainstem below.
Mixed in with the medial forebrain bundle are many relatively large neurons, whose axons frequently join the bundle, reaching as far rostrally as the cerebral cortex, and as far caudally as the spinal cord. The medial integrative nuclei of the hypothalamus can roughly be divided into three groups from rostral to caudal.
The most rostral nuclei, corresponding to the preoptic area, regulate fluid and electrolyte balance, body temperature, and sexual hormones. The middle third of the hypothalamus contains the nuclei that regulate feeding, energy metabolism, stress responses, and coordinate all these with wake-sleep cycles. The caudal third of the hypothalamus contains neurons that are critical for maintaining wakefulness and responding to emergencies.
Strokes of the hypothalamus are vanishingly rare, as the hypothalamus has the most luxuriant blood supply in the brain, befitting a site that is absolutely critical to maintain life. The hypothalamus is what the circle of Willis circles. It is literally surrounded by the internal carotid and basilar arteries, and the blood vessels that connect them. The hypothalamus sits at a crossroads in the brain, receiving direct sensory inputs from the smell, taste, visual, and somatosensory systems.
It also contains within it sensors for such things as blood temperature, blood sugar and mineral levels, and a variety of hormones. Thus the hypothalamus receives sensory inputs necessary to detect challenges in both the internal and external environments.
In addition, the hypothalamus receives inputs from forebrain areas including the hippocampus , amygdala , and cingulate cortex. These structures form the limbic lobe of the brain, which receives highly processed sensory information from throughout the cerebral cortex, and determines it personal importance for the individual. These inputs drive a wide range of emotional responses, and many of the phenomena we associate with emotional expression changes in heart rate, blushing, hair standing on end, etc.
The hypothalamus protects the vital capacity of the organism in three critical ways. First, it must maintain a well regulated internal milieu of electrolyte concentrations and osmolality, glucose and other fuels, and body temperature. The intracellular biochemical machinery of the mammalian body is exquisitely adapted to this environment, and cannot tolerate even small alterations in it.
Similar alterations occur in other tissues, although perhaps with margins that are perhaps not quite so narrow as for the brain. The hypothalamus accomplishes this by having neurons that either receive inputs from sensory systems that monitor these variables, or are themselves sensitive to them.
These neurons attempt to regulate these parameters against what amounts to a setpoint, just as the thermostat in a home is adjusted to a setpoint. In contrast to the homeostatic systems of the hypothalamus, other systems deal with large and unpredictable perturbations of the environment that require a change in behavior and physiology.
These allostatic responses range from recognition of and appropriate adjustments to the presence on the one hand of a mate, and on the other hand of a life threatening attack. The responses can include resetting various setpoints e. In addition to making adjustments of the internal milieu that support homeostasis, and responding to urgent external events, the hypothalamus also helps anticipate daily events that are triggered by the external day-night cycle. Whether animals are diurnal awake in the day or nocturnal awake at night , they have predictable times for feeding, drinking, sleeping, and sexual behavior.
All of these are regulated by the circadian timing system in the brain, so that the body anticipates its various demands and opportunities. For example, wakefulness and cortisol levels peaks at the time of day necessary for an animal to forage for food, while the setpoint for body temperature falls a full degree during the time of day when an animal sleeps.
To exert its control over so many bodily functions, the hypothalamus uses three major outputs: autonomic, endocrine, and behavioral systems. In autonomic control , the hypothalamus contains neurons the send axons directly to the preganglionic neurons for both the sympathetic and parasympathetic nervous systems.
These autonomic control neurons are in the paraventricular and arcuate nuclei, and the lateral hypothalamic area.
This hormone controls many important behaviors and emotions, such as sexual arousal, trust, recognition, and maternal behavior. Also called antidiuretic hormone ADH , this hormone regulates water levels in the body. When vasopressin is released, it signals the kidneys to absorb water. Somatostatin works to stop the pituitary gland from releasing certain hormones, including growth hormones and thyroid-stimulating hormones. Middle region This area is also called the tuberal region.
Posterior region This area is also called the mammillary region. Hypothalamus diagram. Use this interactive 3-D diagram to explore the hypothalamus. Hypothalamus conditions. Several things can cause hypothalamic dysfunction, including: head injuries certain genetic disorders, such as growth hormone deficiency birth defects involving the brain or hypothalamus tumors in or around the hypothalamus eating disorders, such as anorexia or bulimia autoimmune conditions surgery involving the brain Hypothalamic dysfunction plays a role in many conditions, including: Diabetes insipidus.
This causes increased urination and thirst. Unlike people with diabetes mellitus, people with diabetes insipidus have stable blood sugar levels. Prader-Willi syndrome. This is a rare, inherited disorder. It causes the hypothalamus to not register when someone is full after eating.
People with Prader-Willi syndrome have a constant urge to eat, increasing their risk of obesity. Additional symptoms include a slower metabolism and decreased muscle. Many hormones produced by the hypothalamus directly affect those produced by the pituitary gland. Symptoms of hypothalamic conditions. Some symptoms that could signal a hypothalamus problem include: unusually high or low blood pressure body temperature fluctuations unexplained weight gain or loss changes in appetite insomnia infertility short stature delayed onset of puberty dehydration frequent urination.
Tips for a healthy hypothalamus. Get enough sleep A study found that sleep deprivation was associated with hypothalamic dysfunction in rats. Exercise Like eating a balanced diet and getting enough sleep, regular exercise boosts your overall health.
Read this next. Anterior deep temporal artery Medically reviewed by the Healthline Medical Network. Brain Overview. Fornix body Medically reviewed by the Healthline Medical Network. Fornix commissure Medically reviewed by the Healthline Medical Network. Pons Medically reviewed by the Healthline Medical Network. Amygdaloid body Medically reviewed by the Healthline Medical Network.
Putamen Medically reviewed by the Healthline Medical Network. Posterior communicating artery Medically reviewed by the Healthline Medical Network. The preoptic region alongside with the anterior hypothalamic nucleus is involved in cooling thermoregulation of the body through the sweating process. The preoptic nucleus is also involved in the habit of eating and in reproduction while the medial preoptic region is involved in cardiovascular control as a response to stress [ 10 ].
The suprachiasmatic nucleus is situated above the optic chiasm and is involved in the circadian rhythm. The paraventricular nucleus named after its location near the third diencephalic ventricle represents an important autonomic center of the brain involved in stress and metabolism control [ 11 ].
Schematic representation of hypothalamic nuclei sagittal section. The central part as the hypothalamus is located above tuber cinereum and is named the tuberal area. It is composed of two parts, anterior and lateral, and contains the following nucleus: dorsomedial, ventromedial, paraventricular, supraoptic, and arcuate Figure 2. The ventromedial area is involved in controlling the habits of eating and the feeling of satiety [ 12 ]. The arcuate or infundibular nucleus is responsible for orexigenic peptides secretion: ghrelin, orexin, or neuropeptide Y [ 11 ].
The posterior region is formed by a medial and, respectively, lateral area. The medial region contains the mammillary nucleus alongside with the posterior hypothalamic nucleus, the supramammillary and the tuberomammillary ones.
The nucleus of the lateral region contains the hypocretins orexin peptides that control feeding behavior, thermoregulation, gastrointestinal motility [ 13 ], and cardiovascular regulation and are also involved in sleep regulation [ 14 ]. Lesions of the lateral region lead to the refusal to feed or aphagia. The posterior part of the hypothalamus is involved overall in energy balance, blood pressure, memory, and learning.
The posterior hypothalamic nucleus has a major role in controlling the body temperature [ 12 ]. The tuberomammillar nucleus is involved in memory due to their connection with the hippocampus and Papez memory circuit [ 9 ]. The hypothalamus is a small region of the brain connected with numerous, various cerebral structures that allows it to intervene in many regulatory processes of the organism. More, the hypothalamus is involved in the homeostasis of the organism in terms of body temperature, blood pressure, fluid balance, and body weight.
The ascending reticular activating system represents a structure composed by neural fibers passing from the reticular formation of the midbrain, through the thalamus, reaching the cerebral cortex [ 15 ]. The system is responsible for concentration, attention, and for maintaining the awakening state. Through it, the reticular formation is connected with the hypothalamic nuclei: the lateral mammillary bodies [ 12 ], the tuberomammillar nuclei, and the periventricular ones.
The periventricular nuclei receive information about the general visceral sensibility [ 16 ] while the two others mediate behavior and are involved in consciousness [ 17 ]. Information from the solitary tract nucleus passing from the reticular substance of the midbrain can also reach the hypothalamus. The nucleus of the solitary tract is connected with the hypothalamus through either the solitarohypothalamic tract or through colaterales from the solitariothalamic tract. The anterior hypothalamus has connections with the intralaminar nucleus and the nucleus of the median line.
The amygdala represents a conglomerate of perykarions located in the temporal lobe. Efferent fibers from this region project directly to hypothalamus or neural fibers can detach from the amygdala-thalamic fascicle and reach the anterior hypothalamus [ 12 ].
Direct connections of amygdala with the hypothalamus are either through the ventral amygdalofugal pathway or through the stria terminalis. The hippocampus is a curved-shaped cerebral structure located in the temporal lobe. CA1 and CA3 are connected with the infundibular and the ventromedial nuclei of the hypothalamus [ 22 ]. According to a recent study [ 23 ] CA2 area lighted that also CA2 area, a small region in the hippocampus composed from pyramidal neurons, is involved in memory and learning through its connections with the supramammillary nuclei of the hypothalamus.
Fibers from the olfactory bulb reach the periamigdalian region the entorhinal and periamygdaloid cortex and then the lateral hypothalamus through either the amigdalian or the accumbens nucleus [ 12 ]. Visual information from the retinal neuroepithelium through the lateral geniculate body of the mesencephalon and then the superior colliculus reach the suprachiasmatic and supraoptic nuclei of the hypothalamus and are involved in circadian rhythm [ 12 ]. The hypothalamus can receive direct fibers from the retina through a retinohypothalamic tract that reach the suprachiasmatic nuclei.
The connections are involved in the circadian rhythm. There is a double sense connection between the cerebral cortex and the hypothalamus. The hypothalamus projects on the surface of the cortex diffuse, in a poorly defined area over the cortex and transmits information that maintain the cortical tonus while from the gray matter of the cerebral cortex, neural fibers projects over the hypothalamus and triggers visceral response according to the affective state sweating in case of fear, intestinal manifestations in case of stress.
Neural fibers from the lateral hypothalamus project in the prefrontal cortex while the frontal lobe also has efferent for all the hypothalamic regions [ 24 ]. Through these connections, the autonomic control is assured in the organism. More, from the paraorbital gyrus, fibers project into the paraventricular and ventromedial nuclei. Axons from the spinal cord can project in the hypothalamic region using the path of the spinohypothalamic tract.
They carry out pain and temperature information. The hypothalamus exerts its effects within two projections: the spinothalamic tract reaching the lateral horn of the spinal cord of T1-L2 segments regulates the sympathetic autonomic response; the mammillotegmental tract and the dorsal longitudinal fasciculus carry out information from the posterior region of the hypothalamus while the anterior one connects with the thalamus mammillothalamic tract and the above fornix.
In case of high body temperature, the hypothalamus responds through thermoregulatory heat loss behavior either sweating or vasodilatation.
If the body needs to be warm up, hypothalamus can determine heat production behavior vasoconstriction, thermogenesis—heat production from muscles, brain or other organs, including the thyroid gland [ 25 ]. They are of the hypothalamus responsible for controlling this process is the anterior one, more specific the preoptic nucleus.
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. Water control in the living organism is assured by the hypothalamus through the antidiuretic hormone ADH secretion.
In cases of blood volume loss and dehydration, the ADH hormone is secreted from the supraoptic nucleus—that have osmoreceptor cells—and released in the circulation. The peptide is directed toward the specific receptor from kidneys and decreases the urine production with subsequent water retention in the organism.
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