| sternoclavicular muscle | <anatomy> An occasional muscle, a slip from the subclavius muscle, passing from the upper part of the sternum to the clavicle beneath the pectoralis major muscle. Synonym: musculus sternoclavicularis. (05 Mar 2000) |
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| acromioclavicular disk | The articular disk of fibrocartilage usually found between the acromial end of the clavicle and the medial border of the acromion. Synonym: discus articularis acromioclavicularis, acromioclavicular disk, Weitbrecht's cartilage. (05 Mar 2000) |
| Airy disk | <microscopy> The image of a bright point object as focused by a lens system. With monochromatic light, it consists of a central point of maximum intensity surrounded by alternate circles of light and darkness caused by the reinforcement and interference of diffracted rays. The light areas are called maxima and the dark areas minima. The distribution of light from the centre to the outer areas of the figure was investigated mathematically by Sir George Airy. The diffraction disk forms a basis for determining the resolving power of an ideal lens system. The diameter of the disk depends largely on the aperture of the lens. The diffraction of light causing the Airy disk is a factor limiting the resolution of a well corrected optical system. The bright disk of light (surrounded by alternating dark and bright diffraction rings)that is formed by a perfect diffraction-limited lens, focusing an image of an infinitely small source of light. For a minute absorbing spot, the diffraction pattern is a dark Airy disk surrounded by brighter and darker diffraction rings. Since the Airy disk is the smallest unit that makes up the image of a luminous or absorbing object (formed by a properly corrected microscope lens in focus), the radius of the disk determines the limit of resolution of the microscope. (05 Aug 1998) |
| blastodermic disk | The aggregation of blastomeres of a telolecithal ovum after cleavage has occurred. (05 Mar 2000) |
| blood disk | <haematology> A discoid cell (3m diameter) found in large numbers in blood, important for blood coagulation and for haemostasis by repairing breaches (small breaks) in the walls of blood vessels. Platelet _ granules contain lysosomal enzymes, dense granules contain ADP (a potent platelet aggregating factor) and serotonin (a vasoactive amine). They also release platelet-derived growth factor which presumably contributes to later repair processes by stimulating fibroblast proliferation. Synonym: thrombocytes. (09 Oct 1997) |
| bulging disk | A condition that results in the abnormal protrusion (bulging), herniation or prolapse of a vertebral disc from its normal position in the vertebral column. The displaced disc may exert force on a nearby nerve root causing the typical neurologic symptoms of radiating pain (to an extremity), numbness, tingling and weakness. Recurrent episodes of severe back pain are common. Treatment includes non-steroidal anti-inflammatories, corticosteroids and rest. More advanced cases may require surgical intervention (for example laminectomy, micro-disc surgery). (27 Sep 1997) |
| Burlew disk | An abrasive-impregnated rubber wheel used in dentistry for polishing. Synonym: Burlew wheel. (05 Mar 2000) |
| vacuum disk phenomenon | The appearance of a radiolucent stripe in an intervertebral disk, a manifestation of disk degeneration; a misnomer since there is gas present. (05 Mar 2000) |
| Ramsden disk | <microscopy> The small circular patch of light that appears at the eyepoint above the ocular lens. This is the exit pupil of an optical instrument that, in a microscope adjusted for Koehler illumination, lies in a plane conjugate with the objective rear focal plane, condenser iris, and light source. Alteration of the Ramsden disk (for example, by the observer's iris) modifies the aperture function, diffraction pattern, and direction of view of the specimen. (05 Aug 1998) |
| mandibular disk | The fibrocartilaginous plate that separates the joint into upper and lower cavities. Synonym: discus articularis temporomandibularis, mandibular disk, temporomandibular articular disk. (05 Mar 2000) |
| germinal disk | Germ disk, the point in a telolecithal ovum where the embryo begins to be formed. Synonym: embryonic disk, germinal area, area germinativa. (05 Mar 2000) |
| Merkel's tactile disk | A specialised tactile sensory nerve ending in the epidermis, characterised by a terminal cuplike expansion of an intraepidermal axon in contact with the base of a single modified keratinocyte. Synonym: meniscus tactus, Merkel's corpuscle, Merkel's tactile cell, Merkel's tactile disk, tactile disk. (05 Mar 2000) |
| choked disk | papilloedema |
| micrometre disk | <microscopy> A glass disk engraved with a suitable scale, used at the diaphragm of a micrometre ocular. The scale to be focused by the eye lens has to be seen in the field of view. Micrometre eye piece. (05 Aug 1998) |
| ciliary disk | The darkly pigmented posterior zone of the ciliary body continuous with the retina at the ora serrata. Synonym: ciliary disk, ciliary ring, pars plana. Origin: Mod. L. (05 Mar 2000) |