Regeneration of the Retina a Structure of the Retina

figure 5.20 illustrates the structure of the retina. The retina receives photons focused by the lens and converts them to electrical impulses that travel to the optic tectum of the brain. The retina is multilayered in all vertebrates (Ham and Cormack, 1979; Litzinger and Del-Rio Tsonis, 2002). The inner layer consists of the ganglion cells, which give rise to the optic nerve. The photoreceptor layer is composed of the light-transducing segments of the rods and cones that constitute the outer layer of the retina. Between these two layers are several others that vary in number depending on the species, but that always include an inner nuclear layer next to the ganglion cells and an outer nuclear layer closer to the pho-toreceptors. The outer nuclear layer is actually that portion of the rods and cones where their nuclei reside. The inner nuclear layer contains horizontal, bipolar, and amacrine cells that relay impulses from the photorecep-tors to the ganglion cells. The synapses made between the photoreceptors in the outer nuclear layer and the bipolar cells of the inner nuclear layer show up in sections as the outer plexiform layer. A similar inner plexi-form layer is created by the synapses between the neurons of the inner nuclear layer and the ganglion cell layer. The ends of the photoreceptors are embedded in the epithelial cells of the pigmented layer of the retina.

Outside the retina is the retinal pigmented epithelium (RPE) and outside the RPE is the choroid, a layer

Retina Structure Rpe

FIGURE 5.20 Structure of the vertebrate neural retina. (b) Diagram illustrating the nine layers of the neural retina. The internal and external limiting membranes are basement membranes. Muller cells are glia spanning the neural retina. (a) The nine layers of the retina as outlined by silver staining. (c) Histological section stained with hematoxylin and eosin. Reproduced with permission from Stevens and Lowe, Human Histology (3rd ed), Mosby/Elsevier. Copyright 2005, Elsevier.

FIGURE 5.20 Structure of the vertebrate neural retina. (b) Diagram illustrating the nine layers of the neural retina. The internal and external limiting membranes are basement membranes. Muller cells are glia spanning the neural retina. (a) The nine layers of the retina as outlined by silver staining. (c) Histological section stained with hematoxylin and eosin. Reproduced with permission from Stevens and Lowe, Human Histology (3rd ed), Mosby/Elsevier. Copyright 2005, Elsevier.

of heavily vascularized connective tissue. The RPE functions to provide support factors for the photorecep-tors. It transports and regulates the concentrations of ions, water, growth factors and nutrients to the photoreceptors. RPE cells also take up, store and re-isomerize retinol, which is used to synthesize the photopigment rhodopsin.

The retina can be surgically removed from the eye or destroyed by cutting off its blood supply, which results in the degeneration of all retinal neurons. The retina of adult birds and mammals is unable to regenerate after injury with any degree of functional recovery. However, the retina of adult teleost fish and the newt, as well as the retina of some vertebrate embryos, does regenerate.

How To Reduce Acne Scarring

How To Reduce Acne Scarring

Acne is a name that is famous in its own right, but for all of the wrong reasons. Most teenagers know, and dread, the very word, as it so prevalently wrecks havoc on their faces throughout their adolescent years.

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