| back focal plane | <microscopy> The plane, normal to the lens axis, situated at the back focus of a lens. (05 Aug 1998) |
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| back injuries | General or unspecified injuries to the posterior part of the trunk. It includes injuries to the muscles of the back. (12 Dec 1998) |
| back lens | <physics> In any compound lens (a lens system composed of more than one lens element), the last lens through which the light passes is called the back lens. It may be a single simple lens, a doublet, or triplet. See: front lens (05 Aug 1998) |
| back mutation | <molecular biology> A mutation that causes a mutant gene to revert to its original wild-type base sequence. Compare: forward mutation. (09 Oct 1997) |
| back of foot reflex | The foot being firmly supported on its inner side, a sharp tap on the dorsal tendons causes extension of the second to the fifth toes. Synonym: back of foot reflex, dorsum of foot reflex. (05 Mar 2000) |
| back pain | A continuous pain located in the back, usually below the cervical level. For lower back pain or pain in the lumbar region, low back pain is available. (12 Dec 1998) |
| back pain, low | Symptoms in the low back can relate to the bony lumbar spine, discs between the vertebrae, ligaments around the spine and discs, spinal cord and nerves, muscles of the low back, internal organs of the pelvis and abdomen, and the skin covering the lumbar area. The low back, or lumbar area, functions in structural support, movement, and protection of certain body tissue. (12 Dec 1998) |
| back pressure | Pressure exerted upstream in the circulation as a result of obstruction to forward flow, as when congestion in the pulmonary circulation results from stenosis of the mitral valve or failure of the left ventricle. (05 Mar 2000) |
| back teeth | All teeth posterior to the canines. (05 Mar 2000) |
| back-action plugger | An instrument for condensing gold foil or amalgam in areas that cannot be reached directly. (05 Mar 2000) |
| back-knee | Hyperextension of the knee, the lower extremity having a forward curvature. Synonym: back-knee. (05 Mar 2000) |
| back-pressure renal atrophy | <radiology> Caliectasis without obstruction, due to repeated episodes of obstruction, gradual loss of renal pyramids (12 Dec 1998) |
| backache | Non-specific term used to describe back pain; generally refers to pain below the cervical level. (05 Mar 2000) |
| backboard splint | A board splint with slots for fixation by straps; shorter ones are used for neck injuries, longer ones for back injuries. (05 Mar 2000) |
| backbone | <anatomy> The spinal column, found in vertebrate animals, which runs along the dorsal side and contains the central nerve cord (spinal cord). The main structural feature of a polymer (chain-like) molecule from which many side chains branch off. (09 Oct 1997) |