Jacob's Membrane

Labelled diagram of the structure of the retina

Labelled Diagram of the Eye

Labelled diagram of the structure of the retina

Labelled Diagram of the Eye

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.

Recall that light from outside the human body enters the eye through its main structures of the cornea, aqueous humour, pupil, lens, etc. and is normally focussed onto the retina of the eye.

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:

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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