| SM | Master of Science; sadomasochism; self-monitoring; silicon microphysiometer; simple mastectomy; skim... |
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| SMA | sequential multiple analysis or analyzer; sequential multichannel autoanalyzer; simultaneous multich... |
| SMABF | superior mesenteric artery blood flow |
| SMAE | superior mesenteric artery embolism |
| SMAO | superior mesenteric artery occlusion |
| pyrrole nucleus | Of porphyrins, a cyclic tetrapyrrole; four pyrrole groups joined into a ring structure by way of -CH== (methylidyne) bridges between the a position of one pyrrole and the a' position of another pyrrole, the fourth pyrrole being joined to the first. See: porphin, porphyrin. (05 Mar 2000) |
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| shadow nucleus | A nucleus that has lost its pigment and staining properties. (05 Mar 2000) |
| hypoglossal nucleus | The motor nucleus innervating the intrinsic and four of the five extrinsic muscles of the tongue; it is located in the medulla oblongata near the midline, immediately beneath the floor of the inferior recess of the rhomboid fossa. Synonym: nucleus nervi hypoglossi, nucleus of hypoglossal nerve. (05 Mar 2000) |
| solitary nucleus | Gray matter located in the dorsomedial part of the medulla oblongata associated with the solitary tract. The solitary nucleus receives inputs from most organ systems including the terminations of the facial, glossopharyngeal, and vagus nerves. It is a major coordinator of autonomic nervous system regulation of cardiovascular, respiratory, gustatory, gastrointestinal, and chemoreceptive aspects of homeostasis. The solitary nucleus is also notable for the large number of neurotransmitters which are found therein. (12 Dec 1998) |
| somatic nucleus | The larger nucleus (or sometimes nuclei) in ciliate protozoans. Derived from the micronucleus by a process of DNA polytenisation. The DNA in the macronucleus is actively transcribed. The macronucleus degenerates before conjugation. (18 Nov 1997) |
| sperm nucleus | The head of the spermatozoon, which becomes spheroidal, after entering the ovum. See: pronucleus. (05 Mar 2000) |
| spherical nucleus | Spinal nucleus of accessory nerve, a slender column of motor neurons extending longitudinally through the central part of the ventral horn of the upper five segments of the spinal cord, giving origin to the spinal part of the accessory nerve. Synonym: nucleus spinalis nervi accessorii, globosus nucleus. (05 Mar 2000) |
| spinal nucleus of the trigeminus | The long sensory nucleus extending from the caudal border of the pontine sensory nucleus of the trigeminus down through the lateral region of the rhombencephalon into the upper three segments of the spinal cord's dorsal horn; it receives the fibres of the sensory root of the trigeminal nerve which descend along its lateral border as the spinal tract of trigeminal nerve. Synonym: nucleus tractus spinalis nervi trigemini, descending nucleus of the trigeminus, spinal nucleus of the trigeminus. (05 Mar 2000) |
| spinal trigeminal nucleus | The long sensory nucleus extending from the caudal border of the pontine sensory nucleus of the trigeminus down through the lateral region of the rhombencephalon into the upper three segments of the spinal cord's dorsal horn; it receives the fibres of the sensory root of the trigeminal nerve which descend along its lateral border as the spinal tract of trigeminal nerve. Synonym: nucleus tractus spinalis nervi trigemini, descending nucleus of the trigeminus, spinal nucleus of the trigeminus. (05 Mar 2000) |
| Spitzka's nucleus | A small cell group located between the somatic cell columns of the oculomotor nuclei. Since it is placed between the groups of motor neurons innervating, respectively, the left and right medial rectus muscles, the nucleus is considered to possibly represent an integrating mechanism for ocular convergence. Synonym: convergence nucleus of Perlia, Spitzka's nucleus. (05 Mar 2000) |
| Staderini's nucleus | A small collection of nerve cells in the medulla oblongata lying lateral to the hypoglossal nucleus. Synonym: nucleus intercalatus, Staderini's nucleus. (05 Mar 2000) |
| steroid nucleus | tetracyclic steroid nucleus |
| Stilling's nucleus | A column of large neurons located in the base of the posterior gray column of the spinal cord, extending from the first thoracic through the second lumbar segment; it gives rise to the dorsal spinocerebellar tract of the same side. Synonym: nucleus thoracicus, Clarke's column, Clarke's nucleus, dorsal nucleus, nucleus dorsalis, Stilling's column, Stilling's nucleus. (05 Mar 2000) |
| subceruleus nucleus | Diffusely organised nucleus of noradrenergic cells located ventral to the nucleus (locus) ceruleus. (05 Mar 2000) |
| subthalamic nucleus | A circumscript nucleus, shaped like a biconvex lens, located in the ventral part of the subthalamus on the dorsal surface of the peduncular part of the internal capsule immediately rostral to the substantia nigra. The nucleus receives a massive topographic projection from the lateral segment of the globus pallidus, and a somatopically organised projection from the ipsilateral motor cortex; a smaller bundle of afferents from the centromedian nucleus of the thalamus terminate in the rostral part of the nucleus The subthalamic nucleus projects to both pallidal segments, to the pars reticulata of the substantia nigra, and in a small way to the ipsilateral pedunculopontine nucleus. Synonym: nucleus subthalamicus, corpus luysi, Luys' body, nucleus of Luys. (05 Mar 2000) |