nucleus defined in 1951 yearnucleus - nucleus;
nucleus - Body containing the chromosomes present in nearly all cells of plants and animals (eucaryotic organisms). Every nucleus has originated from a previous nucleus, usually by mitosis or meiosis, occasionally by amitosis. Variously shaped, usually spherical or ovoid with firm superficial membrane (nuclear membrane). In the non-dividing cell it usually appears homogeneous in living state, except for one or more nucleoli and granules of heterochromatin; and when fixed contains a darkly staining (basophilic) irregular meshwork. It is highly probable that the organization of the chromosomes is intact in resting cells, and that the homogeneity is deceptive and the meshwork an artefact. At onset of mitosis or meiosis, chromosomes become visible in both living and fixed cell, separating out from a non-basophilic nuclear sap. Nucleus is essential for continued life of most cells (but See also: Red Blood Cell); if it is removed (as by microdissection) remaining cytoplasm soon dies. In procaryotic organisms the DNA is not contained within a nuclear membrane.
nucleus defined in 1951 yearnucleus - nucleus (ofbrain);
nucleus - Demarcated mass of nerve cell-bodies, i.e. of grey matter, in vertebrate brain. A very large number of such nuclei have been anatomically distinguished, though their function is often uncertain. Nuclei are connected by tracts of nerve-fibres. The term is anatomical, not physiological. Compare with: Centre.
near nucleus in Knolik
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