| external acoustic foramen | The orifice of the external acoustic meatus in the tympanic portion of the temporal bone. Synonym: porus acusticus externus, external acoustic foramen, external acoustic pore, external auditory pore, external auditory foramen, orifice of external acoustic meatus. (05 Mar 2000) |
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| external acoustic meatus | The passage leading inward through the tympanic portion of the temporal bone, from the auricle to the tympanic membrane; it consists of a bony (inner) portion and a fibrocartilaginous (outer) portion, the cartilaginous external acoustic meatus. Synonym: meatus acusticus externus, acoustic meatus, antrum auris, auditory canal, external auditory meatus. (05 Mar 2000) |
| external acoustic pore | The orifice of the external acoustic meatus in the tympanic portion of the temporal bone. Synonym: porus acusticus externus, external acoustic foramen, external acoustic pore, external auditory pore, external auditory foramen, orifice of external acoustic meatus. (05 Mar 2000) |
| fundus of internal acoustic meatus | The thin cribriform plate of bone separating the cochlea and vestibule from the internal acoustic meatus; a transverse crest divides it into two regions; in the superior region are located the area nervi facialis and the area vestibularis superior; in the inferior region are located the area cochleae, area vestibularis inferior, and foramen singulare. Synonym: fundus meatus acustici interni, fundus of internal auditory meatus. (05 Mar 2000) |
| abnormalities, radiation-induced | Congenital changes in the morphology of organs produced by exposure to ionizing or non-ionizing radiation. (12 Dec 1998) |
| accidents, radiation | Accidental dispersal of radioactive materials from a radiation source. Accidents at nuclear reactors can involve large groups of the population from dispersion of radioactivity into the environment and through fallout or a few individuals with high injurious doses. (12 Dec 1998) |
| acute radiation syndrome | <syndrome> A syndrome caused by exposure of the body to large amounts of radiation, (e.g., from certain forms of therapy, accidents, and nuclear explosions; it is divided into three major forms which are, in ascending order of severity, the haematogic, gastrointestinal, and central nervous system-cardiovascular forms; its clinical manifestations are divided into prodromal, latent, overt, and recovery stages. (05 Mar 2000) |
| adaptive radiation | <chemistry> The evolution of new speciesor sub-species to fill unoccupied ecological niches. (06 May 1997) |
| alpha radiation | <physics, radiobiology> The most easily absorbable type of radiation, it consists of a stream of alpha particles, doubly ionised helium nuclei which are electrically charged and produce intense ionisation in matter. Alpha radiation can be deflected in electromagnetic fields. (09 Oct 1997) |
| annihilation radiation | The radiation resulting when a positron from beta positive decay comes to rest. It encounters an electron, and they annihilate each other and convert their rest mass into two 0.51-MeV gamma rays emitted in exactly opposite directions. (05 Mar 2000) |
| background radiation | <radiobiology> Level of environmental radation due to background sources. Background sources can be natural, such as cosmic rays and natural radioactive elements (principally radon, but including other elements such as isotopes of potassium (which people get substantial amounts of in foods like bananas)). They can also be man-made, such as from fossil-fuel combustion, everyday leakage from nuclear activities, and leftover from atmospheric nuclear weapons tests. Background radiation is usually distinguished from acute radiation, such as from medical X-rays, nuclear accidents, radioisotope therapy, or other short-term doses. The man-made contribution to background radiation is quite small compared to the natural contribution, medical uses dominate human exposure to acute radiation. (09 Oct 1997) |
| beta radiation | <radiobiology> Radiant energy from a source of beta rays. (05 Mar 2000) |
| radiation | <radiobiology> Propagation of energy through space. In the context of this report, it is electromagnetic radiation (X-rays or gamma rays) or corpuscular radiation (alpha particles, electrons, protons, neutrons) capable of producing ionisation. (16 Dec 1997) |
| radiation anaemia | Hypoplastic anaemia sometimes occurring after high-level acute or low-level chronic exposure to ionizing radiation. (05 Mar 2000) |
| radiation biology | Field of science that studies the biological effects of ionizing radiation. (05 Mar 2000) |