Publication: Fine structure of the retinal photoreceptors of the great horned owl (Bubo virginianus)
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Date
1993
Authors
Braekevelt, Charlie R.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
The retinal photoreceptors of the great
horned owl (Bubo virginianus) consist of rods, single
cones and unequal double cones present in a ratio of
about 30:1:2. In the light-adapted state the rods are stout
cells which are not felt to undergo retinomotor
movements. The rod outer segment consists of a stack of
scalloped membranous discs enclosed by the cell
membrane. The rod inner segment shows an ellipsoid of
mitochondria and a wealth of rough endoplasmic
reticulum (RER) and polysomes, Golgi zones and
autophagic vacuoles but no hyperboloid of glycogen.
Single cones show a slightly tapered outer segment, a
heterogeneous oil droplet and an ellipsoid of
mitochondria at the apex of the inner segment. Double
cones consist of a larger chief member which also
displays an oil droplet and a slightly smaller accessory
member which does not. Both members of the double
cone as well as the single cone show a prominent
ellipsoid, plentiful polysomes and RER and Golgi zones
in the inner segment. Neither single nor double cones
possess a condensed paraboloid of glycogen but instead
show plentiful scattered glycogen particles. Along the
contiguous membranes between accessory and chief
cones a few presumed junctional complexes are seen
near the externa1 limiting membrane. Judging by their
morphology in light-adaptation the cones of this species
do not undergo photomechanical movements. Rods and
cones (both types) have both invaginated (ribbon) and
numerous superficial (conventional) synaptic sites. Rods
are more numerous in this noctumally active bird than is
usually noted in avian species.
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