| Functional significance of the taper of vertebrate cone photoreceptors. | |
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MedLine Citation:
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PMID: 22250013 Owner: NLM Status: Publisher |
Abstract/OtherAbstract:
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Vertebrate photoreceptors are commonly distinguished based on the shape of their outer segments: those of cones taper, whereas the ones from rods do not. The functional advantages of cone taper, a common occurrence in vertebrate retinas, remain elusive. In this study, we investigate this topic using theoretical analyses aimed at revealing structure-function relationships in photoreceptors. Geometrical optics combined with spectrophotometric and morphological data are used to support the analyses and to test predictions. Three functions are considered for correlations between taper and functionality. The first function proposes that outer segment taper serves to compensate for self-screening of the visual pigment contained within. The second function links outer segment taper to compensation for a signal-to-noise ratio decline along the longitudinal dimension. Both functions are supported by the data: real cones taper more than required for these compensatory roles. The third function relates outer segment taper to the optical properties of the inner compartment whereby the primary determinant is the inner segment's ability to concentrate light via its ellipsoid. In support of this idea, the rod/cone ratios of primarily diurnal animals are predicted based on a principle of equal light flux gathering between photoreceptors. In addition, ellipsoid concentration factor, a measure of ellipsoid ability to concentrate light onto the outer segment, correlates positively with outer segment taper expressed as a ratio of characteristic lengths, where critical taper is the yardstick. Depending on a light-funneling property and the presence of focusing organelles such as oil droplets, cone outer segments can be reduced in size to various degrees. We conclude that outer segment taper is but one component of a miniaturization process that reduces metabolic costs while improving signal detection. Compromise solutions in the various retinas and retinal regions occur between ellipsoid size and acuity, on the one hand, and faster response time and reduced light sensitivity, on the other. |
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Authors:
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Ferenc I Hárosi; Iñigo Novales Flamarique |
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Publication Detail:
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Type: JOURNAL ARTICLE Date: 2012-1-16 |
Journal Detail:
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Title: The Journal of general physiology Volume: - ISSN: 1540-7748 ISO Abbreviation: - Publication Date: 2012 Jan |
Date Detail:
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Created Date: 2012-1-17 Completed Date: - Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 2985110R Medline TA: J Gen Physiol Country: - |
Other Details:
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Languages: ENG Pagination: - Citation Subset: - |
Affiliation:
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Laboratory of Sensory Physiology, Marine Biological Laboratory, Woods Hole, MA 02543. |
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From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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