layers of RETINA Flashcards
a complex peripheral nervous mechanism composed of many elements
RETINA
RETINA Came from the word “rete” which means
NETWORK (a network of neurons- visual cells, bipolar cells & ganglionic cells)
thickness of retina
0.1mm - 0.5 mm
retina is attached to the
underlying choroid only at the optic disc and ora serrata
• Consists of a thin, single layer of hexagonal cells which contain minute crystals of a black pigment • Its flat cells are so closely applied to the choroid that in separating the retina from the choroid, the pigment layer is apt to adhere to the choroid • The pigment aids in absorbing light (lacking in albinos)
- RETINAL PIGMENTED EPITHELIUM (RPE)
the elements of the retina which receive the light stimulus & in which is generated the nerve impulse- “visual cells”
Layers of rods and cones/THE VISUAL CELLS (SENSORY EPITHELIUM)- SENSORY NEUROEPITHELIUM
length and diameter of rods
0.06 mm long, 0.002 mm in diameter
number of rods in the each eye
•130,000,000
length and diameter of cones
0.035 mm in length, 0.006 mm in diameter
number of cones in each eye
•6,000,000 in number/eye
•Sieve-like membrane through the perforations of which rods & cones project, not a distinct membrane but a structure formed by the joining of the outer ends of the fibers of Mueller.
EXTERNAL LIMITING LAYER
•Contains the cell bodies of rods and cones
OUTER NUCLEUS LAYER
•Synapse of axons of visual cells & dendrites of bipolar cells & horizontal cells
OUTER MOLECULAR LAYER (OUTER PLEXIFORM LAYER)
cells lying in the inner nuclear layer that make contact with cones (to convey impulses from the visual cells to the ganglionic cells)
BIPOLAR CELLS-
cells that are devoid of dendrons but abundantly supplied with many much branching dendrons which lie wholly within the inner molecular layer
AMACRINE CELLS-
cells in which connect the cones with each other - called association fibers by which one part of the retina may influence another
HORIZONTAL CELLS-
make connections with the axons of the bipolar cells
GANGLIONIC CELLS-
•Contains amacrine, bipolar, & horizontal cells, nuclei of Mueller’s fibers & capillaries of CRA
INNER NUCLEAR LAYER
•Synapse of axons of bipolar cells & dendrites of ganglionic cells & amacrine cells
INNER MOLECULAR LAYER (INNER PLEXIFORM LAYER)
•Contains large cell bodies whose neurons send axons into nerve fiber layer
GANGLIONIC CELL LAYER
•Forms the 90 degree angle
NERVE FIBER LAYER
•Between nerve fiber layer & vitreous; the inner limit of the retina; partially performed by the ends of the Mueller’s fibers
INTERNAL LIMITING LAYER
- the yellow spot- lying about 3.0 mm to the temporal side of the optic disc
MACULA LUTEA
diameter of macula
measures about 1mm - 3.0 mm in diameter
macula is yellowish due to the yellowish pigment in the bipolar cells & ganglionic layers called?
xanthophylls
-Retinal area of greatest visual acuity (in daylight vision) -in the center of macula the retina is very much thinned down (0.1 mm) giving rise to a little pit or depression displacement by the bipolar cells and ganglionic neurons towards the periphery of the macula; leaving only the visual cells layer
FOVEA CENTRALIS
- are found only nerve fibers - absence of the retina renders this spot incapable of receiving impressions of light known as blind spot (Mariotte’s spot)
OPTIC DISC
other term for blind spot
Mariotte’s spot
A small depression in the center of the disc, where CRA enters & the CRV leaves in the eye
PHYSIOLOGICAL CUP
•A dentate line about 8.5 mm back of the sclero-corneal junction
ORA SERRATA- (ORA-MARGIN; SERRA- A SAW)
•3.0-3.5 mm, fibers from the ganglionic cells on reaching the surface of the retina bend at right angles & course over the retina to reach the optic disc
OPTIC NERVE
nerve fibers from the ganglionic cell layer to their exit through the canal
Non-myelinated (medullated) nerve fibers
nerve fibers after passage through canal but they are devoid of neurilemma.
Myelinated (Medullated) nerve fibers
