Cone

A type of specialized light-sensitive cell (photoreceptor) in the retina of the eye that provide sharp central vision and color vision. By contrast, the rods are the retinal photoreceptors that provide side vision and the ability to see objects in dim light (night vision).

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1. A surface joining a circle to a point above the plane (containing the circle). 2. The photosensitive, outward-directed, conical process of a c. cell essential for sharp vision and color vision; cones are the only photoreceptor in the fovea centralis and become interspersed with increasing numbers of rods toward the periphery of the retina. SYN: c. cell of retina. 3. Metallic cylinder or truncated c., either circular or square in cross-section, used to confine a beam of x-rays. SYN: conus (1). [G. konos, c.]

- antipodal c. the set of astral rays of a dividing cell extending from the centriole in a direction opposite to the equatorial plate.

- arterial c. SYN: conus arteriosus.

- c. down to confine a beam of x-rays to a region of interest using a collimator or c. (3); colloq., to focus one's attention or activities.

- elastic c. SYN: conus elasticus.

- gutta-percha c. a c.-shaped, semirigid root canal filling material composed of gutta-percha and zinc oxide.

- Haller cones SYN: lobules of epididymis, under lobule.

- implantation c. SYN: axon hillock.

- c. of light SYN: light reflex (3).

- medullary c. [TA] SYN: conus medullaris.

- nerve growth c. a highly motile structure at the leading edge of an elongating axon.

- ocular c. the c. of light in the interior of the eyeball with the base formed by the rays entering through the pupil and the apex focused on the retina.

- Politzer luminous c. SYN: light reflex (3).

- pulmonary c. SYN: conus arteriosus.

- retinal cones c. (2).

- silver c. pure silver c. with standard conical shape, used with cement to obturate dental root canals.

- theca interna c. the conical thickening of thecal cells of an ovarian follicle with its apex pointed toward the surface.

- twin c. two retinal cones fused together.

- vascular cones SYN: lobules of epididymis, under lobule.

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cone 'kōn n

1) a solid having a circular base and sides that slope evenly to a point

2 a) any of the conical photosensitive receptor cells of the vertebrate retina that function in color vision compare ROD

b) any of a family (Conidae) of numerous somewhat conical tropical gastropod mollusks that include a few highly poisonous forms see CONUS

3) a cusp of a tooth esp. in the upper jaw

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n.

one of the two types of light-sensitive cells in the retina of the eye (compare rod). The human retina contains 6-7 million cones; they function best in bright light and are essential for acute vision (receiving a sharp accurate image). The area of the retina called the fovea contains the greatest concentration of cones. Cones can also distinguish colours. It is thought that there are three types of cone, each sensitive to the wavelength of a different primary colour - red, green, or blue. Other colours are seen as combinations of these three primary colours.

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(kōn) [L. conus, from Gr. konos] 1. a solid figure or body with a circular base tapering to a point; called also conus [TA]. 2. retinal c. 3. in radiology, a conical or open-ended cylindrical structure formerly used as an aid in centering the radiation beam and as a guide to source-to-film distance. Cones were commonly attached to the x-ray tube prior to the use of the collimator. 4. in root canal therapy, a solid substance with a tapered form, usually made of gutta-percha or silver, fashioned to conform to the shape of a root canal. 5. a marine snail of the family Conidae.