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TIME MANAGEMENT (30) (Overview: Inner Clock/Bio-Clock in Human Brain)
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장부영
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2009-08-28 14:47:54, 조회 : 2,556 |
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* Bio-Clock (Inner Clock) in the Human Brain
(1) The Thalamus
The egg-shaped thalamus (thal'ah-mus) makes up 80% of the diencephalon and forms the superoraleral walls of the third ventricle. The right and left thalamus are joined by a small midline commissure, the intermediate mass. Thalamus is a Greek word meaning \\\\\"inner room,\\\\\" which well describes this deep brain region.
The thalamus contains about a dozen major nuclei, each of which sends axons to the cerebral cortex(Figure 12.14). Some thalamic nuclei act as relay stations for the sensory information ascending to the primary sensory areas of the cortex. Afferent impulses from all the conscious senses converge on the thalamus and synapse in at least one of its nuclei. For example, the ventral posterio lateral nucleus. receives general somatic sensory information. The lateral and medial geniculate nuclei (je-nik'u-lat; \\\\\"knee shaped\\\\\") receive visual and auditory information, respectively.
Sensory inputs are not the only type if of information relayed through the thalamus. Every part of the brain that communicated with the cerebral cortex must relay its signals through a nucleus of the thalamus. The thalamus can therefore thought of as the \\\\\"gateway\\\\\" to the cerebral cortex.
The thalamus not only relays information to the cortex but also actively processes the information as it passes through. The thalamic nuclei organize, amplify, or \\\\\"tone down\\\\\" the signala headed for the cerebral cortex. There are many other relay nuclei in the brain, all of which process and \\\\\"edit: information before sending it along.
The division of labor among the different thalamic nuclei is remarkable. Each nucleus receives imput from its own specific region of the CNS and in turn projects information to its own specific region of the cerebral cortex.
(2) The Hypothalamus
The hypothalamus (hi\\\\\"po-thal'ah-mus; \\\\\"below the thalamus) is the inferior division of the diencephalon(Figures 12, 13, 12.15, and 12.16). It forms the inferiolateral walls of the third ventricle. On the underside of the
brain, it lies between the optic chiasma(point of crossover of cranial nerves II, the optic nerves) and the posterior border of the mammillary bodies. The mammillary bodies are rounded bumps that bulge from the hypothalamic floor (mammillary = \\\\\"little breast\\\\\"). The pituitary gland also projects inferiorly from the hypothalamus. This gland secretes many hormones.
The hypothalamus, like the thalamus, contains about a dozen nuclei of gray matter(Figure 12>15). Functionally, the hypothalamus is the main visceral control center of the body, regulating many activities of the visceral organs. Its functions include the following:
1. Control of the autonomic nervous system. As you will recall, the autonomic nervous system is the system of peripheral motor neurons that regulates contraction of smooth and cardiac muscle and the secretion of glands(p. 297). The hypothalamus exerts control over the autonomic neurons. In doing so, it regulates heart rate and blood pressure, movement of the digestive tube, the secretion of sweat glands, and salivary glands and many other visceral activities.
2. Center for emotional response. The hypothalamus lies at the center of emotional part of the brain, the limbic system. Regions involved in pleasure, rag, sex drive. and fear have been located in the hypothalamus.
3. Regulation of body temperature. The body's thermostart is in the hypothalamus. Some hypothalamic neurons sense blood temperature, then initiate the body's cooling or heating mechanisma as needed(sweating , shivering).
4. Hunger and thirst centers. By sensing the concentrations of nutrients and salts in the blood, certain hypothalamic neurones mediate feelings of hunger and thirst.
5. Sleep-wake cycles. Acting with other brain regions, the hypothalamus helps regulate the complex phenomenon of sleep. The hypothalamus is responsible for the timing of the sleep cycle. The nuclei involved seem to be the suprachiasmatic (soo\\\\\"prah-ki-az-mat'ik) nucleus above the optic chiasma and the preoptic nucleus anterior to that(Figure 12.15). The suprachiasmatic nucleus is the body's biological clock, regulating many daily rhythm (circaldian rhythms). It receives information on
daylight-darkness cycles from the eye through the optic nerve, then send signals to the preoptic nucleus. In response to such signals, the preoptic nucleus induces sleep.
6. Control of the endocrine system. The hypothalamus controls the secretion of hormones by the pituitary gland, which in turn regulates many functions of the visceral organs (Chapter 24).
Through experiments that stimulate or remove parts of the hypothalamus, it has become possible to localize each if the above functions to a general regions of the hypothalamus. These regions are called functional centers. For the most part, the functional center can be only roughly matched with specific structural nuclei.
Try to predict some if the functional disorders that result from injuring the hypothalamus.
Hypothalamic lesions cause a number of disorders in visceral functions and in emotions, These can include severe weight loss or obesity, sleep disturbance, dehydration, and a broad range of emotional disorders.
★ Corticotropin releasing hormone (CRH) a factor secreted by the hypothalamus that stimulates the pituitary to release adrenocorticotropic hormone.
★ Adrenocorticotropic. acting on or stimulating the adrenal cortex
★ ACTH. [adrenocorticotropic hormone] (1947) : a protein hormone of the anterior lobe of the pituitary gland that stimulates the adrenal cortex--called also adrenocorticotropic hormone.
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