The Jacob's Membrane (also
known as the "Layer of Rods and Cones")
is the
nineth (9th) of
the layers forming
the retina of
the human eye that light reaches after entering the eye: That is,
after light from outside the body enters the eye through it's main structures
of the cornea, aqueous
humour, pupil, lens,
etc..
The retina is composed of several layers which, together, form
the "screen" in the eye onto which an image of the area
viewed by the eye is formed, and information about that image is
segmented into packets of information that are passed to the
visual cortex of the brain via the optic
nerve.
The Jacob's Membrane is
composed of two types of units, they are rods (which are the more
numerous to the two), and cones.
Although these components are described seperately,
they are also summarised briefly here: |
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Rods: |
|
* __ Approx.
uniform size;
* __ Arranged perpendicularly
to the surface of the layer/retina;
* __ Composed of an
outer and an inner portion - which are of about equal length.
* __ Rhodopsin is located in the outer segments
of the rods.
|
Cones: |
|
* __ Conical shape (hence their
name);
* __ Positioned with the broad
end of the cone in contact with the Layer
8. of the retina;
* __ Composed of an
outer
and
an
inner
segment - with different properties of refraction. |
Each human eye contains approx. 125 million rods
- compared with only approx. 6-7 million cones.
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