Hypothalamus

Hypothalamus - the choronomic subcortical centre of a vegetative nervous system. This subthalamic range of a diencephalon long time is the important object of various scientific researches.

Now the method of implantation of electrodes is widely applied to studying of various structures of a brain. By means of the special stereotaxic technics through a trepanation foramen in a skull introduce electrodes into any set field of a brain. Electrodes are isolated on all extent, their end is free only. Including electrodes in a chain, it is possible sharp local to stimulate those or other regions.

In this work some theoretical and physiological aspects of the given range of a diencephalon are surveyed.

The general functions of a hypothalamus

At backboned the hypothalamus represents the main nerve centre which is responsible for regulation of an internal environment of an organism.

Phylogenetically is old enough part of a brain and consequently at terraneous mammals its constitution is rather identical, unlike the organisation of such younger structures as a new cortex and limbic system.

The hypothalamus controls all basic homeostatic processes. While the decerebrated animal can keep easily enough life, for maintenance of vital activity of an animal with a remote hypothalamus the special intensive measures as at such animal the basic homeostatic mechanisms are destroyed are demanded.

The homeostasis principle consists that at the diversified conditions of an organism bound to its adaptation to sharply variating conditions of environment (for example, at thermal or cold influences, at intensive physical exercise and so on), intrinsic cреда remains to a constant and its parametres fluctuate only in very narrow limens. Presence and high efficacyy of mechanisms of a homeostasis at mammals, and in particular at the human, provide possibility of their vital activity at appreciable changes of environment. Animal, incapable to sustain some parametres of an internal environment, are forced to live in narrower range of parametres of environment.

For example: Ability of frogs to a thermoregulation is so circumscribed, that to persist in the conditions of winter colds, they should alight for a bottom of reservoirs where water will not freeze. On the contrary, many mammals can lead so free existence, as in the summer, despite appreciable fluctuations of temperature in the winter.

From here we perceive, that in connection with weak development of mechanisms of a homeostasis, these animals are less free in the vital activity and if the hypothalamus is removed, is investigatory homeostatic processes the special intensive measures are necessary for maintenance of vital activity of this animal are broken.

Functional anatomy of a hypothalamus

Hypothalamus locating

The hypothalamus represents small part of a brain in weight nearby 5 gramme. The hypothalamus does not possess accurate borders and consequently it can be surveyed as a part of a network of the neurones stretched from a mesencephalon through a hypothalamus to deep parts of a neoncephalon, closely bound to phylogenetically old olfactory system. The hypothalamus is ventral part of a diencephalon, it lays more low (ventral) a thalamus, forming the inferior half of a side of the third ventricle. As the inferior border of a hypothalamus the mesencephalon, and top - a final plate, forward soldering and a visual decussation serves. laterally a hypothalamus the visual tract, an intrinsic capsule and subthalamic structures is located.

Hypothalamus constitution

In a cross-section direction the hypothalamus can be parted to three regions:

1. Periventricular
2. Medial
3. Lateral

Periventricular region represents a thin stria, adjacent to the third ventricle.

In medial region distinguish some the nuclear ranges located in an anteroposterior direction.

The Preoptichesky range phylogenetically belongs to a neoncephalon, however it carry usually to a hypothalamus.

From ventromedial range of a hypothalamus the leg of a pituitary body bridged with adeno - and a neurohypophysis begins. The forward part of this leg wears the name of a median eminence. Processes of many neurones preoptic and a lobby of ranges of a hypothalamus, and also ventromedial and infundibular kernels there terminate; here from these processes the hormones arriving through system of portal pots to a forward lobe of a pituitary body are liberated. Set of nuclear regions in which neurones similar a hormone-producing contain, wear the name hypophysetrope ranges.

Processes of neurones supraoptic and paraventricular kernels go to a back lobe of a pituitary body (these neurones regulate formation and Oxytocinum liberation, or a vasopressin). To bind concrete functions of a hypothalamus to its separate kernels, behind an exception supraoptic and paraventricular kernels, it is impossible.

In a lateralis hypothalamus there are no separate nuclear ranges. Neurones of this region diffusively settle down round a medial fascicle of the neoncephalon going in rostral-caudal a direction from lateralis formations of the establishment of limbic system to the forward centres of a diencephalon. This fascicle consists of long and short ascending and descending fibers.

Eisodic and efferent communications of a hypothalamus

The organisation of eisodic and efferent communications of a hypothalamus testifies that it serves important integrative as the centre for somatic, vegetative and endocrine functions.

The lateral hypothalamus forms bilaterial communications with the top parts of a brainstem, the central grey matter of a mesencephalon and with limbic system. Sensitive signals from a body surface and an internals arrive in a hypothalamus on ascending spinebulboreticular to pathes which conduct in a hypothalamus, either through a thalamus, or through limbic range of a mesencephalon. Other eisodic signals arrive in a hypothalamus on polysynaptic pathways which for the present not all are identified.

Efferent communications of a hypothalamus with vegetative and somatic kernels of a brainstem and spinal cord are formed by the polysynaptic pathways going as a part of a reticular formation.

The medial hypothalamus possesses two-way communications with lateralis, and, besides, it immediately receives signals from some other parts of a brain. In medial range of a hypothalamus there are the special neurones accepting the major parametres of blood and a neurolymph: that is these neurones watch a condition of an internal environment of an organism. They can accept, for example, blood temperature, hydroelectrolitic structure of plasma or the maintenance of hormones in blood.

Through the excitatory mechanisms the medial range of a hypothalamus controls neurohypophysis activity, and through hormonal - an adenohypophysis.

Thus, this range serves as an intermediate link between the excitatory and endocrine system.

Hypothalamus and cardiovascular system

At an electrical boring almost any part of a hypothalamus there can be reactions from cardiovascular system. These reactions mediated first of all by sympathetic system, and also the branches of a vagus nerve going to heart, testify to great value of a hypothalamus for regulation of a hemodynamic from choronomic nerve centres.

The boring of any part of a hypothalamus can be accompanied by inverse changes of a blood flow in different organs (for example, blood flow augmentation in skeletal muscles and simultaneous depression in skin pots). On the other hand, inverse reactions of pots of any organ can arise at a boring of different regions of a hypothalamus. Biological value of similar hemodynamic alterations can be perceived only in the event that to survey them in connection with other physiological reactions accompanying a boring same parathalamic of the regions. Differently, hemodynamic effects of a boring of a hypothalamus are a part of the general behavioural or homeostatic reactions for which this centre answers.

As an example it is possible to result the alimentary and protective behavioural reactions arising at an electrical boring of circumscribed fields of a hypothalamus. During protective behaviour of arterial pressure and a blood stream in skeletal muscles raise, and the blood stream in intestine pots decreases. At a feeding behaviour arterial pressure and a blood stream increases in an intestine, and the blood stream in skeletal muscles decreases. Similar changes of hemodynamic parametres are observed and during other reactions arising in reply to a boring of a hypothalamus, for example at thermoregulatory reactions or a sexual behaviour.

For mechanisms of regulation of a hemodynamic in whole (that is arterial pressure in the big circle of a circulation, warm outlier and blood allocation), reacting by a principle of watching systems, the inferior parts of a brainstem answer. These parts receive the information from arterial baro - and chemoceptors and mechanioreceptors of auricles and ventricles of heart and send signals to various structures of cardiovascular system on sympathetic and parasympathetic efferent fibers. Such bulbar self-control of a hemodynamic is in turn controlled by the higher parts of a brainstem, and in particular a hypothalamus. This regulation is carried out thanks to the excitatory communications between a hypothalamus and preganglionic vegetative neurones. The higher nervous control of cardiovascular system from a hypothalamus participates in all complex vegetative reactions, with which simple self-control has not enough for control, it is possible to carry to such regulations: Thermoregulation, food intake regulation, protective behaviour, physical activity and so on.

Adaptive reactions of cardiovascular system in an operating time

Mechanisms of the adaptation of a hemodynamic at physical work represent theoretical and practical interest. At physical exercise warm outlier (mainly as a result of augmentation of frequency of reductions of heart) raises and simultaneously the blood stream increases in skeletal muscles. At the same time the blood stream through a skin and organs of an abdominal lumen decreases. These adaptive circulatory reactions arise practically simultaneously with the work beginning.

They are carried out by the central excitatory system through a hypothalamus.

The dog at an electrical boring of lateralis range of a hypothalamus at level of mamillary bodies has precisely same vegetative reactions, as well as at run on tredban. At animals in a narcosis condition the electrical boring of a hypothalamus can be accompanied by locomotar certificates and breath increase. By little changes of position of a stimulating electrode it is possible to achieve vegetative from each other vegetative and somatic reactions. All these effects are eliminated at bilateral lesions of the conforming regions; at dogs with such lesions adaptive reactions of cardiovascular system to work disappear, and at run on tredban, such animals quickly get tired. These data testify that in lateralis range of a hypothalamus the bunches of neurones which are responsible for acclimatisation of a hemodynamic to muscular work are located. In turn these parts of a hypothalamus are supervised by a brain cortex. It is not known, whether such regulation by the isolated hypothalamus as for this purpose it is necessary that to a hypothalamus the special signals of skeletal muscles arrived can be carried out.

Hypothalamus and behaviour

The electrical boring of small fields of a hypothalamus is accompanied by occurrence at animal typical behavioural reactions which are so various, as well as natural species-specific types of behaviour of a concrete animal. Major of such reactions are defensive behaviour and flight, a feeding behaviour (nutrition and water consumption), a sexual behaviour and thermoregulatory reactions. All these behavioural complexes provide a surviving of the individual and a kind and consequently it is possible to name them homeostatic processes in a broad sense this word. The structure of each of these complexes includes somatic, vegetative and hormonal components.

At a local electrical boring of the caudal ring the awake cat has a defensive behaviour which hissing, apostatis of dactyls shows in such typical somatic reactions as wriggle backs, leting off unguises, and also vegetative reactions - a hurried breathing, dilating of pupils and piloerection in the field of a back and a tail. Arterial pressure and a blood stream thus increase in skeletal muscles, and the blood stream in an intestine decreases. Such vegetative reactions are bound mainly to excitation of adrenergic sympathetic neurones. In protective behaviour participate not only somatic and vegetative reactions, but also hormonal factors.

At a boring of caudal part of a hypothalamus pain stimulations cause only defensive behaviour fragments. It testifies that the excitatory mechanisms of defensive behaviour are in a back part of a hypothalamus.

The feeding behaviour also bound to structures of a hypothalamus, on the reactions is almost inverse to defensive behaviour. The feeding behaviour arises at an aboriginal electrical boring of region located of 2-3 mm regions of defensive behaviour are more dorsal. In this case all reactions, characteristic for an animal in questings are observed. Having approached to a bowl, the animal with is artificial the caused feeding behaviour starts to eat, even if it is not hungry, and thus chews inedible subjects.

At research of vegetative reactions it is possible to find, that such behaviour is accompanied by the enlarged salivation, rising of a motility and blood supply of an intestine and depression of a muscular blood flow. All these typical changes of vegetative functions at a feeding behaviour serve as though as a preparatory stage to food intake. During a feeding behaviour activity of parasympathetic nerves of a gastrointestinal tract raises.

Principles of the organisation of a hypothalamus

Data of regular researches of a hypothalamus by means of a local electrical boring testify that in this centre there are the excitatory structures controlling the diversified behavioural reactions. In experiences with use of other methods - for example, destruction or a chemical boring is a position it has been confirmed and dilated.

Example: an aphagia (abandoning of nutrition), arising at lesions of lateralis ranges of the hypothalamus which electrical boring leads to a feeding behaviour. Destruction of medial ranges of the hypothalamus, which boring inhibits a feeding behaviour (the saturation centres), is accompanied by a hyperphagia (nutrition overconsumption).

The hypothalamus ranges which boring leads to behavioural reactions, are widely blocked. In this connection for the present it was not possible to secure functional or anatomical clumps of the neurones which are responsible for this or that behaviour. So, the kernels of a hypothalamus taped with the help neurohystologic of methods, only rather approximately correspond to the ranges which boring is accompanied by behavioural reactions. Thus, the excitatory formations providing formation of integrated behaviour from separate reactions, it is not necessary to survey as accurately outlined anatomical structures (on what existence of such terms as "the hunger centre" and "the saturation centre" could push).

The neural organisation of a hypothalamus thanks to which this small formation is capable to control set of the vital behavioural reactions and neurohumoral regulatory processes, remains a riddle.

Probably, bunches of neurones of the hypothalamus, responsible for performance of any function, differ from each other eisodic and efferent communications, mediators, a locating of dendrites and so forth. It is possible to assume, that in the excitatory chains of a hypothalamus poorly studied by us numerous programs are put in pawn. Activization of these programs under the influence of the excitatory signals from overlying parts of a brain (for example limbic system) and signals from receptors and an organism internal environment can lead various behavioural and neurohumoral to regulatory reactions.

Functional disorders at humans with hypothalamus damages

At the human of disturbance of activity of a hypothalamus happen are bound mainly to neoplastic (tumoral), traumatic or inflammatory lesions. Similar lesions can be rather circumscribed, grasping forward, mediate or back part of a hypothalamus. At such patients complex functional disorders are observed. Character of these disorders is defined, among other things, by acuteness (for example at traumas) or duration (for example, at slowly growing tumours) process. At the circumscribed acute lesions there can be appreciable functional disturbances while at slowly growing tumours these disturbances start to show only at far come process.

In the table complex functions of a hypothalamus and disturbance of these functions are listed. Disorders of perception, memory and a cycle a sleep/wakefulness are particulate bound to damage of the ascending and descending pathes bridging a hypothalamus with limbic system.