| SNR | selective nerve root [block]; signal-to-noise ratio; substantia nigra zona reticulata; supernumerary... |
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| substantia grisea centralis | In general: the predominantly small-celled gray matter adjoining or surrounding the central canal of the spinal cord and the third and fourth ventricles of the brainstem, in particular: the thick sleeve of gray matter surrounding the cerebral sylvian aqueduct in the midbrain, rostrally continuous with the posterior nucleus of the hypothalamus; in sections stained for myelin it stands out from the adjoining tectum and tegmentum by the poverty of its myelinated fibres. Synonym: substantia grisea centralis. (05 Mar 2000) |
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| substantia innominata | Tissue in the base of the forebrain inferior to the anterior perforated substance, and anterior to the globus pallidus and ansa lenticularis. It contains the nucleus basalis of meynert and may be implicated in alzheimer's disease. (12 Dec 1998) |
| substantia intermedia centralis et lateralis | The central gray matter of the spinal cord surrounding the central canal. Synonym: substantia intermedia centralis et lateralis, anterior gray column, Stilling's gelatinous substance, substantia gelatinosa centralis. (05 Mar 2000) |
| substantia lentis | That which constitutes the lens of the eye, composed of a nucleus and a cortex and covered by an epithelium. Synonym: substantia lentis. (05 Mar 2000) |
| substantia medullaris | The inner portion of an organ. (09 Oct 1997) |
| substantia muscularis prostatae | The smooth muscle in the stroma of the prostate. Synonym: substantia muscularis prostatae, musculus prostaticus. (05 Mar 2000) |
| substantia nigra | A large cell mass, crescentic on transverse section, extending forward over the dorsal surface of the crus cerebri from the rostral border of the pons into the subthalamic region; it is composed of a dorsal stratum of closely spaced pigmented (i.e., melanin-containing) cells, the pars compacta, and a larger ventral region of widely scattered cells, the pars reticulata; the pars compacta in particular includes numerous cells that project forward to the striatum (caudate nucleus and putamen) and contain dopamine, which acts as the transmitter substance at their synaptic endings; other, apparently non-dopaminergic cells of the substantia nigra project to a rostral part of the ventral nucleus of thalmus, the middle layers of the superior colliculus and to restricted parts of the reticular formation of the midbrain; the nigrostriatal projection is reciprocated by a massive striatonigral fibre system with multiple neurotransmitters, chief among which is gamma-aminobutyric acid (GABA); substantia n. Receives smaller afferent projections from the subthalamic nucleus, the lateral segment of the globus pallidus, the dorsal nucleus of the raphe and the pedunculopontine nucleus of the midbrain. The pars reticulata forms part of the output system for the striate body. The substantia n. Is involved in the metabolic disturbances associated with Parkinson's disease and Huntington's disease. Synonym: locus niger, nucleus niger, Soemmerring's ganglion. (05 Mar 2000) |
| substantia ossea dentis | <dentistry> A bony substance covering the root of a tooth. (08 Jan 1998) |
| substantia perforata anterior | A region at the base of the brain through which numerous small branches of the anterior and middle cerebral arteries (lenticulostriate arteries) enter the depth of the cerebral hemisphere; it is bordered medially by the optic chasm and anterior half of the optic tract, rostrally and laterally by the lateral olfactory stria; its anteromedial part corresponds to the olfactory tubercle. Synonym: substantia perforata anterior, locus perforatus anticus, olfactory area. (05 Mar 2000) |
| substantia perforata posterior | The bottom of the interpeduncular fossa at the base of the midbrain, extending from the anterior border of the pons forward to the mamillary bodies, and containing numerous openings for the passage of perforating branches of the posterior cerebral arteries. Synonym: substantia perforata posterior, locus perforatus posticus, Malacarne's space. (05 Mar 2000) |
| substantia propria corneae | Proper substance of cornea, modified transparent connective tissue, between the layers of which are open spaces or lacunae nearly filled with the corneal cells or corpuscles. Synonym: substantia propria corneae. (05 Mar 2000) |
| substantia propria membranae tympani | Proper substance of tympanic membrane, the layer of radial and circular collagenous fibres of the tympanic membrane. (05 Mar 2000) |
| substantia propria of cornea | Proper substance of cornea, modified transparent connective tissue, between the layers of which are open spaces or lacunae nearly filled with the corneal cells or corpuscles. Synonym: substantia propria corneae. (05 Mar 2000) |
| substantia propria sclerae | Proper substance of the sclera, the dense white fibrous tissue arranged in interlacing bundles that forms the main mass of the sclera, continuous anteriorly with the substantia propria corneae. (05 Mar 2000) |
| substantia reticularis | A filamentous plasmatic material, beaded with granules, demonstrable by means of vital staining in the immature red blood cells. Synonym: alpha substance, filar mass, filar substance, substantia reticularis, substantia reticulofilamentosa. Synonym: reticular formation. (05 Mar 2000) |