| nuclei nervorum cranialium | Groups of nerve cells associated with the cranial nerves either as motor nuclei (nuclei originis) or sensory nuclei (nuclei terminationis). Synonym: nuclei nervorum cranialium. (05 Mar 2000) |
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| nuclei of cranial nerves | Groups of nerve cells associated with the cranial nerves either as motor nuclei (nuclei originis) or sensory nuclei (nuclei terminationis). Synonym: nuclei nervorum cranialium. (05 Mar 2000) |
| nuclei of mamillary body | A single large-celled lateral nucleus and a larger bipartite medial nucleus together comprising the mamillary body; present in the caudal hypothalamus. Synonym: nuclei corporis mamillaris, nucleus of the mamillary body. (05 Mar 2000) |
| nuclei of origin | Collections of motor neurons (forming a continuous column in the spinal cord, discontinuous in the medulla and pons) giving origin to the spinal and cranial motor nerves. Synonym: nuclei originis, motor nuclei. (05 Mar 2000) |
| nuclei originis | Collections of motor neurons (forming a continuous column in the spinal cord, discontinuous in the medulla and pons) giving origin to the spinal and cranial motor nerves. Synonym: nuclei originis, motor nuclei. (05 Mar 2000) |
| nuclei parabrachiales | The cell groups flanking the brachium conjunctivum at levels immediately caudal to the inferior colliculus; they serve as way-stations in the pathways ascending from the nucleus of solitary tract to the thalamus and hypothalamus, and receive afferent fibres from the hypothalamus and amygdaloid body. Synonym: nuclei parabrachiales. (05 Mar 2000) |
| nuclei pontis | 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) |
| nuclei raphes | Collections of small neurons centrally scattered among many fibres from the level of the trochlear nucleus in the midbrain to the hypoglossal area in the medulla oblongata. (12 Dec 1998) |
| nuclei tegmenti | Collective term for two small round cell groups in the caudal part of the midbrain (caudal pontine tegmental nucleus, nucleus tegmenti pontis caudalis and oral pontine tegmental nucleus, nucleus tegmenti pontis oralis), associated with the mamillary body by way of the mamillary peduncle and mamillotegmental tract. Synonym: nuclei tegmenti, Gudden's tegmental nuclei. (05 Mar 2000) |
| nuclei terminationis | Tetracyclic steroid nucleus, the group of four fused rings forming the framework or parent substance of the steroids. Synonym: perhydrocyclopenta[a]phenanthrene, steroid nucleus, terminal nuclei. (05 Mar 2000) |
| nuclei tuberales | Two or three small, encapsulated, round or ovoid clusters of cells in the lateral hypothalamic area along the surface of the tuber cinereum; their connections and functional significance are unknown. Synonym: nuclei tuberales, lateral tuberal nuclei. (05 Mar 2000) |
| nucleic acid | <biochemistry, molecular biology> Linear polymers of nucleotides, linked by 3', 5' phosphodiester linkages. In DNA, deoxyribonucleic acid, the sugar group is deoxyribose and the bases of the nucleotides adenine, guanine, thymine and cytosine. RNA, ribonucleic acid, has ribose as the sugar and uracil replaces thymine. DNA functions as a stable repository of genetic information in the form of base sequence. RNA has a similar function in some viruses but more usually serves as an informational intermediate (mRNA), a transporter of amino acids (tRNA), in a structural capacity or, in some newly discovered instances, as an enzyme. The spontaneous loss of the amino groups of cytosine (yielding uracil), methyl cytosine (yielding thymine) or of adenine (yielding hypoxanthine). It can be argued that the presence of thymine in DNA in place of the uracil of RNA stabilises genetic information against this lesion, since repair enzymes would restore the GU base pair to GC. (18 Nov 1997) |
| nucleic acid base | A purine or pyrimidine; found in naturally occurring nucleic acids such as DNA. (05 Mar 2000) |
| nucleic acid conformation | The characteristic 3-dimensional shape of a nucleic acid or polynucleotide. Its secondary structure is due to the formation of hydrogen bonds between nucleotides, resulting in base pairing and areas with alpha helix structure. (12 Dec 1998) |
| nucleic acid denaturation | Disorganization of secondary structures of nucleic acids through cleavage of hydrogen bonds and hydrophobic linkages. Denatured DNA appears to be a single-stranded flexible structure. The effects of denaturation on RNA are similar though less pronounced and largely reversible. (12 Dec 1998) |