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I R GIBBONS

Publications and source records attributed to I R GIBBONS.

11 recordsLinked to original sources
PubMed1963

THE VISUAL CELLS AND VISUAL PIGMENT OF THE MUDPUPPY, NECTURUS.

Electron microscopy of the visual cells of the mudpuppy Necturus have revealed several new or hitherto neglected features of organization: (a) A system of deeply staining micelles in virtually crystalline array, probably located in the lamellae of the rod outer segments. These particles may contain the visual pigment, porphyropsin. Counts of the micelles, and microspectrophotometric measurements of porphyropsin in the retina and single rods yield the estimate that each lamellar micelle may contain about 50 molecules of porphyropsin. (b) Systems of about 30 cytoplasmic filaments (here called dendrites), continuous with the cytoplasm of the inner segment, and standing like a palisade about the outer segments of the rods and cones. In the rods, one such filament stands in the mouth of each of the approximately 30 deep fissures that carve the outer segment into a radial array of lobules. (c) A system of deeply staining particles in the membranes of the dendrites, and another in the membranes of the pigment epithelial processes. It is suggested that these may have a part in interchanges of material with the outer segments. The ciliary process is found to penetrate more deeply than is commonly supposed into the outer segments of the rods and cones. The edge of each double-membrane disc in rods forms a differentiated rim structure, both around the disc circumference and bordering the fissures. These anatomical arrangements are summarized in Figs. 13 and 14, and the relevant measurements in Table I. The dilution of visual pigment in Necturus rods and cones and a general consideration of their microstructures make it seem unlikely that such typically solid state processes as exciton migration or photoconduction can transport the effects of light far from the site of absorption. Excitation must, therefore, be conveyed to the receptor as a whole by some axial structure. Among axial structures, the plasma membrane is most likely to be the site of nervous excitation. The ciliary process probably plays its main role in the embryogenesis and regeneration of outer segments; and the dendrites and pigment epithelial processes in exchanges of material with the outer segments and perhaps with one another.

Animals↗
PubMed1961

The relationship between the fine structure and direction of beat in gill cilia of a lamellibranch mollusc.

This paper describes the fine structure and its relationship to the direction of beat in four types of cilia on the gill of the fresh-water mussel Anodonta cataracta. The cilia contain nine outer, nine secondary, and two central fibers, such as have been described previously in other material. Each outer fiber is a doublet with one subfiber bearing arms. One particular pair of outer fibers (numbers 5 and 6) are joined together by a bridge. The two central fibers are enclosed by a central sheath; also present in this region is a single, small mid-fiber. The different groups of fibers are connected together by radial links that extend from the outer to the secondary fibers, and from the secondary fibers to the central sheath. The basal body consists of a cylinder of nine triplet fibers. Projecting from it on one side is a dense conical structure called the basal foot. The cylinder of outer fibers continues from the basal body into the cilium, passing through a complex transitional region in which five distinct changes of structure occur at different levels. There are two sets of fibers associated with the basal bodies: a pair of striated rootlets that extends from each basal body down into the cell, and a system of fine tubular fibers that runs parallel to the cell surface. The relationship between fine structure and direction of beat is the same in all four types of cilia examined. The plane of beat is perpendicular to the plane of the central fibers, with the effective stroke toward the bridge between outer fibers 5 and 6, and toward the foot on the basal body.

Animals↗
PubMed1960

On flagellar structure in certain flagellates.

This paper describes the structure of the flagella, basal bodies, and some of the associated fibre systems in three genera of complex flagellates, Trichonympha, Pseudotrichonympha, and Holomastigotoides. Three groups of longitudinal fibres occur in a flagellum: two central and nine outer fibres such as have been repeatedly described in other material, and an additional set of nine smaller secondary fibres not previously identified as such. Each central fibre shows a helical substructure; the pair of them are enveloped in a common sheath. Each outer fibre is a doublet with one subfibre bearing projections-called arms-that extend toward the adjacent outer fibre. The basal body is formed by a cylinder of nine triplet outer fibres. Two subfibres of each triplet continue into the flagellum and constitute the doublets. The third subfibre terminates at the transition of basal body to flagellum, possibly giving rise to the nine radial transitional fibres that seem to attach the end of the basal body to the surface of the organism. The central and secondary flagellar fibres are not present in the lumen of the basal body, but other complex structures occur there. The form of these intraluminal structures differs from genus to genus. The flagellar unit is highly asymmetrical. All the flagella examined have possessed the same one of the two possible enantiomorphic forms. At least two systems of fibres are associated with the basal bodies of all three genera.

Animals↗
PubMed1957

The fine structure of nuclei during sperm maturation in the locust.

1. In the heads of maturing sperm of a locust the chromatin becomes arranged in a highly regular manner so as to produce many parallel lines about 60 A thick in longitudinal section and contiguous polygons in transverse section. 2. This configuration appears after fixation in osmium tetroxide, formaldehyde, or acetic acid; intermediate stages in its development are illustrated. 3. These electron micrographs are interpreted to mean that, during sperm maturation, the chromatin becomes formed into sheets and then into tubes running parallel with the long axis. 4. In the mature sperm head we have been unable so far to detect this structure. This may be because the chromatin becomes so compact during the shrinkage of the nucleus which occurs during formation of the mature sperm.

Animals↗