| PAG | periaqueductal gray region |
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| vlPAG | ventrolateral periaquaductal gray |
| gray-scale ultrasonography | The display of the ultrasound echo amplitude or signal intensity as different shades of gray, improving image quality compared to the obsolete black and white presentation. (05 Mar 2000) |
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| gray substance | The cortex of the brain which contains nerve cell bodies. The gray matter is in contrast to the white matter, the part of the brain that contains myelinated nerve fibres. The gray matter is so named because it in fact appears gray. The white matter is white because that is the colour of myelin, the insulation covering the nerve fibres. In the mysterious affair at styles (1920), agatha christie first quoted the fictional belgian detective hercule poirot in regard to his gray matter: 'this affair must be unravelled from within.' he tapped his forehead. 'these little grey cells. It is up to them as you say over here.' (12 Dec 1998) |
| gray syndrome | <syndrome> Gray baby syndrome, gray appearance of an infant at birth and during the neonatal period which can be caused by transplacental toxic effects of the drug chloramphenicol taken by the mother during late pregnancy; the syndrome may be fatal. (05 Mar 2000) |
| gray wedge | <microscopy> An elongated rectangular pattern whose brightness changes from black through shades of gray to white along its length. In calibration wedges, the brightness may vary linearly or logarithmically in discrete steps. (05 Aug 1998) |
| gray wing | A prominence in the floor of the inferior fovea of the fourth ventricle that overlies the dorsal motor nucleus of the vagus. Synonym: trigonum nervi vagi, ala cinerea, ashen wing, gray wing, trigone of vagus nerve, va'gi eminentia. (05 Mar 2000) |
| middle gray layer of superior colliculus | See: gray layer of superior colliculus. Molecular layer, term applied to any layer of brain tissue that contains few nerve-cell bodies and is composed largely of terminal arborizations of dendrites and axons; notable examples are the superficial layer (first layer) of the cerebral cortex and the molecular layer of cerebellum. Synonym: plexiform layer, stratum moleculare. (05 Mar 2000) |
| pontine gray matter | The massive gray matter filling the basilar pons. The nuclei are of fairly homogeneous architecture and project to the cortex of the contralateral cerebellar hemisphere by way of the middle cerebellar peduncle. Their main afferents come from the entire extent of the cerebral neocortex by way of the longitudinal pontine bundles (corticopontine fibres); thus, the pontine nuclei form a major way-station in the impulse conduction from the cerebral cortex of one hemisphere to the posterior lobe of the opposite cerebellum. Synonym: nuclei pontis, pontine gray matter. (05 Mar 2000) |
| heterotopic gray matter | <radiology> Presence of cortical neurons in an abnormal location secondary to arrest of migrating neuroblasts from ventricular walls to brain surface between 7-24 weeks of gestational age, frequency: 3% of healthy population associated with: agenesis of corpus callosum, aqueductal stenosis, microcephaly, schisencephaly, encephalocele X-ray: single/multiple bilateral subependymal nodules along lateral ventricles Differential diagnosis: subependymal spread of neoplasm, subependymal haemorrhage, vascular malformation, tuberous sclerosis, intraventricular meningioma, neurofibromatosis (12 Dec 1998) |
| superficial gray layer of superior colliculus | See: gray layer of superior colliculus. (05 Mar 2000) |
| deep gray layer of superior colliculus | A layer of myelinated fibres, the deepest layer of the colliculus superior, delimiting the latter from the central gray substance surrounding the cerebral aqueduct. Synonym: stratum album profundum. (05 Mar 2000) |
| digital gray scale | 1. Extent from side to side, or distance sidewise from a given point or line; breadth; width. "Provided the length do not exceed the latitude above one third part." (Sir H. Wotton) 2. Room; space; freedom from confinement or restraint; hence, looseness; laxity; independence. "In human actions there are no degrees and precise natural limits described, but a latitude is indulged." (Jer. Taylor) 3. Extent or breadth of signification, application, etc.; extent of deviation from a standard, as truth, style, etc. "No discreet man will believe Augustine's miracles, in the latitude of monkish relations." (Fuller) 4. Extent; size; amplitude; scope. "I pretend not to treat of them in their full latitude." (Locke) 5. <geography> Distance north or south of the equator, measured on a meridian. 6. <astronomy> The angular distance of a heavenly body from the ecliptic. Ascending latitude, Circle of latitude, Geographical latitude, etc. See Ascending. Circle, etc. High latitude, that part of the earth's surface near either pole, especially. That part within either the arctic or the antarctic circle. Low latitude, that part of the earth's surface which is near the equator. Origin: F. Latitude, L. Latitudo, fr. Latus broad, wide, for older stlatus; perh. Akin to E. Strew. Source: Websters Dictionary (01 Mar 1998) |