| nuclear fission | Nuclear reaction in which the nucleus of a heavy atom such as uranium or plutonium is split into two approximately equal parts by a neutron, charged particle, or photon. (12 Dec 1998) |
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| nuclear fusion | Thermonuclear reaction in which the nuclei of an element of low atomic weight unite under extremely high temperature and pressure to form a nucleus of a heavier atom. (12 Dec 1998) |
| nuclear heart scan | This noninvasive test uses radioactive tracers to delineate the hearts chambers and major vessels. It may be used to detect a heart attack, heart muscle function and coronary artery disease. The patient receives a radioactive tracer by injection (into a vein) and then the heart is imaged using a gamma camera. The heart is imaged before and after exercise. This test may be used to detect and evaluate atrial septal defect, dilated cardiomyopathy, congestive heart failure, cardiomyopathy, Lyme disease (secondary), mitral stenosis and superior vena cava syndrome. (27 Sep 1997) |
| nuclear hyaloplasm | The presumably fluid substance or gel of the nucleus in which stainable elements were believed to be suspended; much that was formerly considered to be karyolymph is now known to be euchromatin. Synonym: nuclear hyaloplasm, nuclear sap, nucleochylema, nucleochyme. Origin: karyo-+ L. Lympha, clear water (05 Mar 2000) |
| nuclear inclusion bodies | See: inclusion bodies. (05 Mar 2000) |
| nuclear jaundice | <paediatrics> Disorder due to jaundice in a newborn baby with high blood levels of the pigment bilirubin that is deposited in the brain resulting in damage. The level of bilirubin is monitored in newborns to determine whether treatment is needed to prevent kernicterus. With brain affected, it is also called bilirubin encephalopathy. (12 Dec 1998) |
| nuclear lamina | <cell biology> A fibrous protein network lining the inner surface of the nuclear envelope. The extent to which this system also provides a scaffold within the nucleus is controversial. Proteins of the lamina are lamins A, B and C, which have sequence homology to proteins of intermediate filaments. (18 Nov 1997) |
| nuclear layers of retina | The outer nuclear layer, layer 4, of the retina, neuroepithelial layer of retina, and the inner layer, layer 6, of the retina, ganglionic layer of retina. Synonym: granular layers of retina, stratum nucleare externum et internum retinae. (05 Mar 2000) |
| nuclear localization signal | Short, predominantly basic amino acid sequences identified as nuclear import signals for some proteins. These sequences are believed to interact with specific receptors at nuclear pores. (12 Dec 1998) |
| nuclear magnetic resonance | Spectroscopic method of measuring the magnetic moment of atomic nuclei in a covalent bond. Clinical application is in biochemical, metabolic, and physiologic studies of living tissue. It includes proton and electron spin-echo and spin-relaxation times. (12 Dec 1998) |
| nuclear magnetic resonance imaging | A special imaging technique used to image internal stuctures of the body, particularly the soft tissues. An MRI image is often superior to a normal X-ray image. It uses the influence of a large magnet to polarize hydrogen atoms in the tissues and then monitors the summation of the spinning energies within living cells. Images are very clear and are particularly good for soft tissue, brain and spinal cord, joints and abdomen. These scans may be used for detecting some cancers or for following their progress. Acronym: MRI (11 Nov 1997) |
| nuclear magnetic resonance tomography | A special imaging technique used to image internal stuctures of the body, particularly the soft tissues. An MRI image is often superior to a normal X-ray image. It uses the influence of a large magnet to polarize hydrogen atoms in the tissues and then monitors the summation of the spinning energies within living cells. Images are very clear and are particularly good for soft tissue, brain and spinal cord, joints and abdomen. These scans may be used for detecting some cancers or for following their progress. Acronym: MRI (11 Nov 1997) |
| nuclear magnetic resonance, biomolecular | Nmr spectroscopy on small- to medium-size biological macromolecules. This is often used for structural investigation of proteins and nucleic acids, and often involves more than one isotope. (12 Dec 1998) |
| nuclear magneton | A constant in the equation relating the difference in energies between parallel and antiparallel spin alignments of atomic nuclei in a magnetic field; used in nuclear magnetic resonance spectrometry. (05 Mar 2000) |
| nuclear matrix | <cell biology> Membrane system that surrounds the nucleus of eukaryotic cells. Consists of inner and outer membranes separated by perinuclear space and perforated by nuclear pores. The term should be used in preference to the term nuclear membrane which is potentially very confusing. (18 Nov 1997) |
| indirect nuclear division | <cell biology> A method of indirect division of a cell, consisting of a complex of various processes, by means of which the two daughter nuclei normally receive identical complements of the number of chromosomes characteristic of the somatic cells of the species. Mitosis, the process by which the body grows and replaces cells, is divided into four phases. 1. Prophase: formation of paired chromosomes, disappearance of nuclear membrane, appearance of the achromatic spindle, formation of polar bodies. 2. Metaphase: arrangement of chromosomes in the equatorial plane of the central spindle to form the monaster. Chromosomes separate into exactly similar halves. 3. Anaphase: the two groups of daughter chromosomes separate and move along the fibres of the central spindle, each toward one of the asters, forming the diaster. 4. Telophase: the daughter chromosomes resolve themselves into a reticulum and the daughter nuclei are formed, the cytoplasm divides, forming two complete daughter cells. NOTE: the term mitosis is used interchangeably with cell division, but strictly speaking it refers to nuclear division, whereas cytokinesis refers to division of the cytoplasm. In some cells, as in many fungi and the fertilized eggs of many insects, nuclear division occurs within the cell unaccompanied by division of the cytoplasm and formation of daughter cells. (13 Nov 1997) |
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| internal nuclear layer of retina | The intermediate layer of neurons in the retina composed largely of bipolar cells. Synonym: internal nuclear layer of retina, stratum ganglionare retinae, stratum nucleare internum retinae. (05 Mar 2000) |
| epstein-barr virus nuclear antigens | Nuclear antigens encoded by epstein-barr virus genes. at least six nuclear antigens have been identified but their mechanism of action and role in B-cell transformation is still unknown. (12 Dec 1998) |
| external nuclear layer of retina | The outermost layer of the cerebral layer of retina, composed of the primary receptor cells of the retina; the stratum consists of two sublayers: 1) an external layer made up of the rods and cones, the photosensitive processes of the receptor cells, and 2) the external nuclear layer containing the cell bodies of these cells; the external limiting membrane forms a perforated supporting plate between the two sublayers; the name refers to the fact that the retinal receptor cells are a specialised form of (epithelial) ependyma cell and thus, in a sense, are comparable to the neuroepithelial cells (e.g., hair cells) of other sense organs. Synonym: external nuclear layer of retina, stratum neuroepitheliale retinae, stratum nucleare externum retinae. (05 Mar 2000) |
| U1 small nuclear RNA-(guanosine-N2)-methyltransferase | <enzyme> A trans-active non-small nuclear ribonucleoprotein; facilitates the formation of the m3g cap Registry number: EC 2.1.1.- Synonym: u1 snrna(g-n2)mtase (26 Jun 1999) |
| U6 small nuclear RNA methyltransferase | <enzyme> Methylates gamma-phosphate residues in rnas; distinct from u6 snrna n6-adenosine methyltranferase; mw 130 kD; from hela cells Registry number: EC 2.1.1.- Synonym: u6 snrna capping enzyme (26 Jun 1999) |