Question

Describe the neural layer of the retina- including all cell types and their functions.

Answer 1

Retina consists of 3 types of cells and their synapses arranged (from without inward) in the following ten layers
1. Pigment epithelium. outermost layer of retina. It consists of a single layer of cells containing pigment and is firmly adherent to the underlying basal lamina of the choroid.
2. Layer of rods and cones. Rods and cones are the end organs of vision and are also known as
photoreceptors. There are about 120 millions rods and 6.5 millions cones. Rods contain a photosensitive substance visual purple (rhodopsin) and helps in peripheral vision and vision of low illumination (scotopic vision). Cones also contain a photosensitive substance and is responsible for photopic vision and colour vision.
3. External limiting membrane. It is a fenesterated membrane, through which the processes of rods and cones pass.pass
4. Outer nuclear layer. It consists of nuclei of the rods and cones.
5. Outer plexiform layer. It consists of connections of rod spherules and cone pedicles with the dendrites of bipolar cells and horizontal cells.

6.Inner nuclear layer. It mainly consists of cell bodies of bipolar cells. It also contains cell bodies of horizontal amacrine and Muller’s cells and capillaries of central artery of retina. The bipolar cells constitute the first order neurons.
7. Inner plexiform layer. connections between the axons of bipolar cells dendrites of the ganglion cells, and processes of amacrine cells occur in this layer
8. Ganglion cell layer. It mainly contains the cell bodies of ganglion cells (the second order neurons of visual pathway). There are two types of ganglion cells.: (1) The midget ganglion cells which are present in the macular region and the dendrite of each such cell synapses with the axon of single bipolar cell. (2)Polysynaptic ganglion cells lie predominantly in peripheral retina and each such cell may synapse with upto a hundred bipolar cells.
9. Nerve fibre layer consists of axons of the ganglion cells, and it passes through the lamina cribrosa to form the optic nerve.
10. Internal limiting membrane. It is the innermost layer and separates the retina from vitreous. It is formed by the union of terminal expansions of the Muller’s fibres, and is essentially a basement membrane.
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