**4. Connections of the hypothalamus**

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. It has an important role in the optimal, normal functioning of the body, and it controls the endocrine system, the metabolism, and it is involved in stress control and in other different actions that modulates a person's behavior. More, the hypothalamus is involved in the homeostasis of the organism in terms of body temperature, blood pressure, fluid balance, and body weight.

The connections of the hypothalamus are made with the following structures.

#### **4.1. The midbrain**

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.

#### **4.2. The thalamus**

The anterior hypothalamus has connections with the intralaminar nucleus and the nucleus of the median line. Recent studies described that lesions of the intraluminal group of nucleus can lead to Parkinson's disease [18] or even schizophrenia [19]. The mammillothalamic fascicle of Vicq d'Azyr connects both the medial and lateral mammillary nuclei with the anterior part of the thalamus [20]; its destruction in case of a cerebral hemorrhage is associated with memory loss [17, 20].

#### **4.3. The amygdala**

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 hippo-

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. It has an important role in the optimal, normal functioning of the body, and it controls the endocrine system, the metabolism, and it is involved in stress control and in other different actions that modulates a person's behavior. 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

The anterior hypothalamus has connections with the intralaminar nucleus and the nucleus of the median line. Recent studies described that lesions of the intraluminal group of nucleus can lead to Parkinson's disease [18] or even schizophrenia [19]. The mammillothalamic fascicle of Vicq d'Azyr connects both the medial and lateral mammillary nuclei with the anterior part of the thalamus [20]; its destruction in case of a cerebral hemorrhage is associated with

The connections of the hypothalamus are made with the following structures.

campus and Papez memory circuit [9].

8 Hypothalamus in Health and Diseases

**4.1. The midbrain**

solitariothalamic tract.

**4.2. The thalamus**

memory loss [17, 20].

**4. Connections of the hypothalamus**

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]. It is involved in body's response to fear and rewards but also in memory [21]. Direct connections of amygdala with the hypothalamus are either through the ventral amygdalofugal pathway or through the stria terminalis.

#### **4.4. The hippocampal region**

The hippocampus is a curved-shaped cerebral structure located in the temporal lobe. It is formed by the dentate gyrus and different regions called Cornus Ammonis (CA): CA1, CA2, CA3, and CA4 [22]. 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.

#### **4.5. The olfactory bulb**

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].

#### **4.6. The retina**

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.

#### **4.7. Cerebral cortex**

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.

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

Anatomy and Function of the Hypothalamus http://dx.doi.org/10.5772/intechopen.80728 11

The hypothalamus regulates both sympathetic and parasympathetic systems. The anterior region of the thalamus has an excitatory effect over the sympathetic system while the poste-

The endocrine control is realized through the pituitary gland or the hypophysis situated below the tuberal region of the hypothalamus. The hypothalamus is connected with the posterior lobe of the gland through the hypothalamo-hypophyseal tract. Along these fibers, the AHD and oxytocin hormones are transported into the neurohypophysis where they are

Hormones secretion in the body is regulated by the hypothalamus through the releasing and inhibitor factors: thyrotropin-releasing, gonadotropin-releasing, corticotrophin-releasing, somatostatin, and dopamine. These hormones are involved in the process of growth, in the reproduction, in the metabolism of the body, and also can assure the homeostasis of the

The reproduction function of an organism is assured by the hypothalamic-pituitary-gonadal axis. The gonadotropin-realizing hormone (GnRH) secreted by the hypothalamus stimulates the production of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the anterior subdivision of the pituitary gland. Action of these two hormones on the gonads

Behavior in males and females is influenced as well by the sex steroids. The neurons in the preoptic are involved in the male sexual behavior while the ones from the tuberal regional

The photosensible suprachiasmatic nucleus is involved, along with is connections with the pituitary gland, in the circadian rhythm. The suprachiasmatic nucleus receives electro-chemical information from the stimulated retina. The circadian rhythm represents the endogenous clock of an organism that is involved in the well-being of the body due to keeping within

Despite its reduced size, the hypothalamus represents an important, integrative region of the brain with complex functions and multiple connections with essential cerebral structures.

rior and lateral ones have an excitatory effect over the parasympathetic system.

urine production with subsequent water retention in the organism.

**5.4. Center for autonomic nervous system**

determines the estrogen and testosterone production.

exert their properties in females [26].

normal limits the major functions.

**5.7. The circadian rhythm**

**5.5. Endocrine control**

stocked in vesicles.

**5.6. Reproduction**

body.
