The hypothalamus is the Mainly responsible for motivational behavior. He is in charge of letting us know that we are hungry or thirsty. It also helps our body maintain a constant temperature. This part of the brain control the pituitary gland, which is the gland that controls all other endocrine glands in the body. Therefore, the hypothalamus plays a key role in the connection of the endocrine system with the nervous system.
Located on the midbrain and under the thalamus, the hypothalamus forms the ventral diencephalon. The diencephalon is an embryonic region of the vertebrate neural tube that gives rise to the posterior structures of the anterior brain.
Thisformed by several neuronal groupings, all interrelated. However, each of these nuclei has its complex pattern of connections with different areas of the brain. It is composed of different areas and nuclei, with a very diversified functional pattern.
- 1 The hypothalamus and the endocrine system
- 2 Autonomous systems and somatic motor
- 3 The hypothalamus and aggressiveness
The hypothalamus and the endocrine system
Two of the most prominent hypothalamic nuclei (because their neurons are large) are the paraventricular nucleus and the supraoptic nucleus. The cells of these nuclei secrete two types of hormones in the bloodstream: oxytocin, which causes uterine contraction during birth and induces the release of milk in females with young and antidiuretic hormone (ADH) It travels to the kidneys to help the body retain water by decreasing urinary production.
Other hypothalamic nuclei, located in the anterior area, regulate blood levels of growth hormone, adrenocorticotropic hormone (for the stress response), thyrotropin (which regulates basal metabolism) and the other hormones that regulate the reproductive organs and sexual behavior
Through its connections with the hypophysis, also plays a key role in the neuroendocrine secretion control. The hypothalamic neurons that participate in endocrine control are, fundamentally, the magnocellular neurons, the supraoptic and paraventricular nuclei, and the parvicellular neurons of the periventricular zone.
Autonomous systems and somatic motor
Several hypothalamic nuclei with brainstem projections regulate and modulate the functioning of the autonomous system and somatic motor.
The hypothalamus, however, is not only a brain area responsible for the control of the somatic, motor and endocrine system, but it seems to be a coordinating center, capable of integrating emotional and sensory information, in order to generate an appropriate efferent response to the situation in which the subject is.
The hypothalamus coordinates emotional expression through the regulation of neuroendocrine, motor and autonomous systems.
In 1932, Stephen Ranson implanted electrodes in different areas of the hypothalamus. Through electrical stimulation of the different regions of the hypothalamus, Ranson generated various autonomic reactions to experimental animals, such as alterations in capillary erection, alterations in gastrointestinal and bladder motility, blood pressure or heart rate, among others.
The hypothalamus and aggressiveness
It is believed that the Hypothalamus also has a very important role in emotion regulation. Specifically, its lateral areas seem to be involved with pleasure and anger, while the middle part is mainly connected with aversion, disgust and the tendency to uncontrollable and strong laughter. However, in general terms, the Hypothalamus has more to do with the expression (symptomatic manifestation) of emotions than with the genesis of affective states.
In the twenties, different experimental studies with cats and dogs showed that the lesion of the posterior half of the hypothalamus prevented the manifestation, in the same animals, of aggressive behaviors induced by excisions of the cerebral hemispheres.
A researcher at the University of Zurich, Walter R. Hess, showed that electrical stimulation of various locations in the hypothalamus could induce different attack and defense responses.
Engraving by Darwin that illustrates the emotional defense response of a cat to the threat of a dog.
W.R. Hess studied the effects of electrical stimulation of several areas of the diencephalon and found a variety of responses depending on the specific area stimulated. Thus, this researcher showed that the electrical stimulation of the hypothalamus was able to generate in the animals characteristic patterns of emotional responses of fear and rage. In 1949, Hess received the Nobel Prize for his work on the role of the hypothalamus in the coordination and functional regulation of internal organs.
In 1971, Panksepp found that when the electrical stimulation of the hypothalamus generated predatory aggression, this stimulation was reinforced by animal, while when it generated threat behaviors, it turned out to be aversive. Panksepp came to this conclusion because in the first case the rats easily learned to self-provide stimulation currents in the lateral hypothalamus by means of a lever, while in the second they learned very easily to disconnect the electrical stimulation when it was provided in the medial hypothalamus.
In the 1970s, the researcher at the Yale University School of Medicine, John Flynn, saw that the electrical stimulation of the medial hypothalamus could generate attack threat behaviors in cats; These behaviors were accompanied by high activity of the sympathetic branch of the autonomic nervous system. When the stimulation was, however, of lateral hypothalamus caused a predatory aggression without this high sympathetic activity.
Stimulation of the medial hypothalamus in cats generates threat behaviors that warn the adversary that he will be subject to aggression if he is still present in the situation.Source: M.F. Bear, B.W. Connors, M. A. Paradiso A: Neuroscience. Exploring the brain. (2001). Ed.: Lippincott Williams & Wilkins.
Stimulation of the lateral hypothalamus generates predatory attacks by a member of one species towards a member of another.Source: M.F. Bear, B.W. Connors, M. A. Paradiso A: Neuroscience. Exploring the brain. (2001). Ed.: Lippincott Williams & Wilkins.
Experiments conducted by Shaikh, Siegel and collaborators have revealed the interconnections between the amygdala, the hypothalamus and the gray periaqueductal substance for the development, both of the attack threat aggression (referred to by some authors as affective aggression, due to the high sympathetic activity observed in behavioral patterns), as well as predatory aggression.
So, we see how the hypothalamus regulates behavioral patterns aggressive through two anatomically differentiated pathways and has a very important role in coordinating the peripheral expression of emotional states.
Functionally The hypothalamus is related to aspects such as homeostatic regulation, motivated behaviors or emotions.
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