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.
For more information about related subjects see:
*_ Structure
& Components of the Eye,
*_ Components
of the Central Nervous System,
*_ The
Pathway of a Nerve Impulse,
*_ Structures
and Functions of Neurones,
*_ Diseases
and Disorders of the Nervous System,
*_ Text
books about Ophthalmology. |
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