| somatic hybrid | Heterokaryon formed between two somatic cells, usually from different species. See: somatic cell genetics. (18 Nov 1997) |
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| somatic layer | The external layer of the lateral mesoderm of the embryo, lying adjacent to the ectoderm and together with it constituting the somatopleure. (05 Mar 2000) |
| somatic mesoderm | That portion of the embryonic mesoderm that is associated with the body wall and is divided from the splanchnic visceral) mesoderm by the coelomic cavity. (18 Nov 1997) |
| somatic mitosis | The ordinary process of mitosis as it occurs in the somatic or body cells, characterised by the formation of the prescribed number of chromosomes, appropriate for the species (in humans the number is 46). (05 Mar 2000) |
| somatic motor neuron | See: motor neuron. (05 Mar 2000) |
| somatic motor nuclei | Collective term indicating the motor nuclei innervating the tongue musculature (hypoglossal nucleus) and the extraocular eye muscles (abducens nucleu, trochlear nucleus, and oculomotor nucleus). (05 Mar 2000) |
| somatic mutation | Mutation that occurs in the somatic tissues of an organism and that will not, therefore, be heritable, since it is not present in the germ line. Some neoplasia is due to somatic mutation, a more conspicuous example is the reversion of some branches of variegated shrubs to the wild type (completely green) phenotype. Somatic mutation is probably also important in generating diversity in V gene regions of immunoglobulins. (18 Nov 1997) |
| somatic mutation theory of cancer | That cancer is caused by a mutation or mutations in the body cells (as opposed to germ cells), especially nonlethal mutations associated with increased proliferation of the mutant cells. (05 Mar 2000) |
| somatic nerve | <anatomy, nerve> One of the nerve's of parietal sensation or voluntary motion, as distinguished from the visceral sensory, involuntary motor and secretory nerve's. (05 Mar 2000) |
| 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) |
| somatic recombination | One of the mechanisms used to generate diversity in antibody production is to rearrange the DNA in B-cells during their differentiation, a process that involves cutting and splicing the immunoglobulin genes. Somatic recombination via homologous crossing over occurs at a low frequency in Aspergillus, Drosphilia and Saccharomyces and in mammalian cells in culture. It may be detected through the production of homozygous patches or sectors after mitosis of cells heterozygous for suitable marker genes. (18 Nov 1997) |
| somatic reproduction | Asexual reproduction by fission or budding of somatic cells. (05 Mar 2000) |
| somatic sensory cortex | Somatosensory cortex, the region of the cerebral cortex receiving the somatic sensory radiation from the ventrobasal nucleus of the thalamus; it represents the primary cortical processing mechanism for sensory information originating at the body surfaces (touch) and in deeper tissues such as muscle, tendons, and joint capsules (position sense); it corresponds approximately to Brodmann's areas 1, 2, 3 on the postcentral gyrus. Synonym: somesthetic area. (05 Mar 2000) |
| somatic swallow | A swallowing pattern with muscular contractions which appear to be under control of the person at a subconscious level; distinguished from visceral swallow. Visceral swallow, the immature swallowing pattern of an infant or a person with tongue thrust, resembling peristaltic wavelike muscular contractions observed in the gut; adult or mature swallowing is more volitional and therefore somatic. (05 Mar 2000) |
| special somatic afferent column | A column of gray matter in the hindbrain of the embryo, represented in the adult by the nuclei of the auditory and vestibular nerves. (05 Mar 2000) |