Article about encephalon by The Free Dictionarythe anterior section of the central nervous system in vertebrate animals and man, located in the cranial cavity. The brain is the material basis of higher nervous activity and the chief regulator of all life functions of the organism. In invertebrate animals that have a central nervous system, brain function is performed by the cephalic ganglion, which is developed among higher insects and mollusks to such an extent that it is also called a brain. The brain consists of the telencephalon (the cerebral hemispheres); the diencephalon, which includes the thalamus, hypothalamus, metathalamus, and epithalamus; the mesencephalon, which includes the cerebral peduncle and the corpora quadrigemina; the metencephalon, which consists of the pons and the cerebellum; and the medulla oblongata, which is a direct continuation of the spinal cord. All sections located between the spinal cord and the diencephalon form the brain stem; through it pass the afferent (centripetal, sensory) nerve fibers, which are directed from the spinal cord and the cranial nerves to the higher sections of the brain, and the efferent (centrifugal, motor) nerve fibers, which go in the reverse direction. The brain stem contains groups of specific afferent nerve cells (nuclei) that receive information from the skin and muscle receptors in the head region, as well as from other sense organs (hearing, equilibrium, taste). Also located in the brain stem are an aggregate of cells in the form of a structure known as the reticular formation, as well as a number of nerve centers that govern vitally important functions (for example, respiration, blood circulation, and digestion). A primitive brain is already present in the lancelet. In the vertebrate series the brain gradually becomes more complex and the divisions enumerated above are formed. The progressive complexifica- tion of the brain can be traced during embryonic development. The brain attains its highest development in man. On the average, the adult human brain weighs 1. Simeons hCG Weight Loss Program; Articles Bio-Mesotherapy; Common Cold Remedies; Estrogen Toxicity Part 1. How to Reset the Hypothalamus for Weight Loss. The hypothalamus is also related to thyroid function, which controls metabolism and is linked to effectiveness of weight loss efforts.The diencephalon comprises the hypothalamus, epithalamus, and thalamus, the latter consisting of the ventral thalamus, or subthalamus. Diet & Weight Management; Weight Loss & Obesity; Food & Recipes; Fitness & Exercise; Beauty & Balance. Healthy Beauty; Health & Balance; Sex & Relationships. Explanation of encephalon. All sections located between the spinal cord and the diencephalon form the brain stem; through it pass the afferent. HCG is also of great utility in obese diabetics through its diencephalon regulation and associated weight loss. HCG will also decrease the amount of esterified cholesterol. HCG Diet; Weight Loss Issues. The relative mass of the brain, however, according to the index of la. Roginskii, is highest in man (for man, 3. Enlargement of the surface of the cerebral hemisphere in man and the higher animals has occurred through an increase in the number of furrows and cerebral convolutions that form the lobes of the hemispheres (for example, the frontal, parietal, temporal, and occipital lobes, the insula, and the gyrus cinguli). The cerebral hemispheres of the brain consist of three principal elements. The first of these is a surface layer of gray matter called the cerebral cortex. The thickness of this layer in man is 1–5 mm. The number of its neurons totals approximately 1. In the cortex, as well as in other brain structures, there are glial cells (neuroglia, or glia), which participate in the metabolic processes of neural tissue, perform a supportive function, and possibly play some sort of specific role in brain activity. The second major substance is the white matter, formed by neural fibers that travel to the brain from the periphery and to the periphery from the brain, as well as by fibers that connect the various areas of the cortex and both hemispheres. The third element consists of a number of subcortical ganglia (basal ganglia), embedded within the hemispheres (that is, in the midst of the white matter but consisting of gray matter); the most important of these ganglia are the corpus striatum and the globus pallidus. The brain is covered by the dura mater, the arachnoidea encephali, and the pia mater, between which is found the cerebrospinal fluid (which also fills the cavities of the cerebral ventricles). The circulatory system of the brain and the cerebrospinal fluid serve as channels of transport for nutrients, oxygen, and other substances necessary for the life activities of the neurons. Decomposition products are removed from the brain along the same channels. The brain is extremely sensitive to oxygen insufficiency. The brain may be considered, according to a number of anatomical and functional characteristics, as an aggregate of sensory systems. The receptors (nerve endings) of any afferent system receive stimuli, which are then sent in the form of nervous impulses along the centripetal neural pathways to the brain. Currents of nervous impulses carry information to the brain about the strength and nature of the stimuli received by the receptors of the sensory organs (for example, the eyes, ears, and skin) and all internal organs, muscles, and tendons. In the subcortical structures, then in the cortical sections of the analyzers, and ultimately by the whole cortex, this information is processed—that is, analyzed and synthesized. The brain then sends commands to the executive organs (efferent systems) about the character of responsive reaction to the stimuli. The responsive reactions may be of two types—unconditioned reflexes or conditioned reflexes. Motor reflexes are primarily a function of the extrapyramidal system, which consists of the subcortical ganglia; the corpus striatum receives impulses from the thalamus and from the cortex and transmits them to the globus pallidus, whence they enter the nuclei of the brain stem and finally the motor neurons of the anterior horns of the spinal cord. In lower vertebrates (fishes, amphibians, and reptiles) this is the only system of motor coordination; in mammals there is, in addition, the pyramidal system, along which impulses from the cortex are transmitted directly to the motor neurons of the spinal cord. This system attains its highest level of development in the apes and man, and it provides the most complex conditioned- reflex and voluntary movements. The pyramidal system, being interconnected with the extrapyramidal, at this level of development takes over the leading role. Unconditioned autonomic reactions (for example, vascular, secretory, metabolic) are a function of the nerve centers of the thalamus, hypothalamus, and other structures of the brain stem. The cerebral cortex is connected with these structures as well; a number of autonomic conditioned reactions may therefore arise. Normal operation of the brain is possible only at a certain level of irritability of its principal divisions. There are three paths for maintaining that level. The first is through the reticular formation of the brain stem, into which impulses enter along branches (collaterals) of the centripetal paths to the thalamus and from there to the appropriate regions of the cortex. After processing in the reticular formation, the nervous impluses lose the specific features of belonging to a particular analyzer and become nonspecific. These impulses are directed at the appropriate moment along ascending paths to all regions of the cerebral cortex, activating them and imparting a certain level of irritability (tonus). The second path for the maintenance of cortical tonus is through the sympathetic nervous system and the cerebellum. The third path is through specific pathways that lead away from the sense organs. Conditioned- reflex mechanisms may also take part in the maintenance of tonus. It is presumed that the higher vertebrates have some cortical self- regulation (including self- regulation of cortical tonus), which is especially well developed in man. Self- regulation of tonus is provided by bilateral links between the cortex and the reticular formation, and also between the sympathetic nervous system and the cerebellum. Intensive investigation is being done on the self- regulatory mechanisms of the brain that ensure those levels of higher nervous activity in man that are called thought and consciousness and are determined by the ability of the brain to receive, process, and store information and give out the results of the processing. The limbic system plays an important role in brain activity. It is located on the interior surface of the cerebral hemispheres and deep within the lateral ventricles. It consists of the hippocampus, septum, amygdaloid bodies, pyriform and cingulate gyri, mamillary bodies, and fimbria; the thalamus and hypothalamus (and a number of other structures) are sometimes also considered part of its composition. It is postulated that the limbic system is related to certain kinds of memory and to the instinctive hereditary reactions that make for an inborn basis for the emotions. Disturbances of certain kinds of memory have been noted in humans where there is significant destruction of the hippocampus and amygdaloid nuclei. Patients remember events preceding this kind of operation, but if distracted they are unable to recall what they intended to do five or ten minutes before. Destruction of certain structures of the limbic system in animals is accompanied by the disruption of sequential activity; the animal, not yet having completed one movement, begins another. Electrical stimulation of the amygdaloid bodies, septum, and hypothalamus in monkeys induces pugnacity, aggressiveness, and increased sexual activity. Moreover, mutual relations between certain individuals in a group may change; a subordinate monkey may become dominant, and vice versa. Despite significant progress in the study of brain function, for which science is greatly indebted to the classic works of I. Sherrington, the internal mechanisms of its integrative activity and coordination remain as yet unexplained. In this connection the structure and functions of the brain are undergoing intensive study in the laboratories and clinics of many countries by means of physiological, clinical, biochemical, biophysical, morphological, cybernetic, and other methods of investigation. REFERENCESShmal’gauzen, I. Osnovy sravnitel’noi anatomii pozvonochnykh zhivotnykh, 4th ed. Pages 2. 25–7. 6. Orbeli, L. Voprosy vysshei nervnoi deiatelnosti. Moscow- Leningrad, 1. Pages 3. 97–4. 19, 4. Pavlov, I. Moscow- Leningrad, 1. Pages 3. 20–4. 4. Bykov, K. Pages 3. Sechenov, I. Refleksy golovnogo mozga. Moscow, 1. 96. 1.
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