Adult Macula Essay

5.Nissl bodies are in the soma of the nucleus and are made up ofrough ER.

 A.accommodation B.the concentration of cones in the fovea C.chemical structure of the vitreous humor D.the prevalence of amacrine cells in the

Also, on the retina is the optic disk. There are no photoreceptors in this area, so any light that falls on this part of the retina is unseen and creates what is called the blind spot. (Hugh

This setup has several advantages, as there is less movement in the subretinal region than the epiretinal region, and subretinal alignment is less prone to breakage and inflammation. Also, subretinal implants can act as a replacement for lost photoreceptors, the natural visionary tool for processing light images, due to their corresponding alignments. Subretinal alignment also has its disadvantages, such as the increase in stimulus threshold in comparison to epiretinal placement due to an increase in stimulus distance. Subretinal also has a difficult and daunting surgical process, and the blind retina is different from a functional retina causing a need for more than a photoreceptor replacement for the patient(Shepherd et al., 2013).

What are rods and cones? Where are they found? What is the macula? What is the optic disk?

In this study, experimenters selectively lesioned layers 1-2 (M pathway) and 3-6 (P pathway), then mapped out the corresponding visual field area that suffered the lesions. They found that lesions of the P geniculate layers generated severe impairments in contrast sensitivity and stereoscopic vision at high spatial frequencies, as well as color, texture, pattern, and one of the shape discrimination tasks (Fig x). Lesion to M layers, on the other hand, produced impairment in flicker detection and the two motion detection tasks they studied. Interestingly, they noticed that neither M or P lesions alone led to significant impairment in brightness discrimination, or in coarse shape discrimination. These findings imply that M pathway seems sufficient to preserve some shape discrimination, and challenges the view that P pathway is the sole input for extrastriatal form

According to current research there are about 800,000 ganglion cells in the human optic nerve (J.R. Anderson, 2009,pg. 35). The ganglion cells are where the first encoding of the visual information happens. Encoding is the process of recognizing the information and changing it into something one’s brains can understand and store. Each ganglion cell is dedicated to encoding information from a specific part of the retina. The optic nerve goes then to the visual cortex and the information enters the brain cells. There are two types of cells that are subcortical, or below the cortex; the lateral geniculate nucleus and the superior colliculus. The lateral geniculate nucleus is responsible for understanding details and recognizing objects. The superior colliculus is responsible for understanding where objects are located spatially. This collection of cells working together is called the “what-where” distinction. The division of labor continues, as the information is further processes. The “what” information travels to the temporal cortex, the “where” information travels to the parietal regions of the brain.

Tapeta can be classified according to their location in vertebrates and mechanism in invertebrates. Choroidal tapeta are the most common and are classified as tapetum fibrosum and tapetum cellulosum. The simplest type is the tapetum fibrosum, which is found principally in mammals, including herbivores (elephants, horses and goats), cetaceans (whales and dolphins), certain marsupials (Tasmanian Devil), and a rodent (Cuniculus pacas). The tapetum fibrosum consists of extracellular collagen fibrils that are stacked orderly with the majority of the its fibers running horizontally. The number of layered fibrils varies between species and can be up to several hundred thick. The most studied tapetum fibrosum among mammals is found in the cow and is located posteriorly and dorsally. The thickness is variable, increasing its thickness posteriorly. In species with a choroidal tapetum, the retinal epithelium in the area is the tapetum in un-pigmented, it allowing the light to pass subsequently reflected by the tapetum. This contrasts with the pigmented retinal epithelium

To understand how macular degeneration affects the eye, we must first know how the eye itself functions and why it is important to have the macula intact. A heathy eye is made of different layer that helps people to see colors, movement and to see images plainly. The macula is part of the retina, the retina is

The preganglionic fibres are myelinated and project out of the cord via the ventral root. From there

There are two layers that make up the iris. The innermost layer is called the iris pigment epithelium and is of neuroectodermal origin. The outer layer is of mesodermal origin and is named the iris stroma. The iris stroma contains connective tissue which holds nonpigmented fibroblasts as well as pigmented melanocytes (Imesch et. al. 1997). Eye

The visual system contains two types of photoreceptors, the rods and the cones. These two receptors are easily distinguishable from one another based on their individual shapes, which also gives them their names. They also differ in the type of photopigments they each contain, in the way they are diffused across the retina, and by the variances between their synaptic associations (Purves, Augustine, Fitzpatrick, Katz, LaMantia, McNamara & Williams, 2001). Rods are found in the periphery of the eye and react to faint light, for example black and white, which allows the visual system to process twilight vision. Cones, on the other hand, are located primarily in the fovea and they respond to brighter lights, allowing for the ability to see things in color and are accountable for daylight vision.

Photoreceptors gather visual information by absorbing light and sending electrical signals to other retinal neurons for initial processing and integration. The signals are then sent via the optic nerve to other parts of brain, which ultimately processes the image and allows us to see.

The retina converts light energy into signals that are carried to the brain. In the centre of the retina is where the cone cell are located. The cone cells are responsible for absorbing coloured light waves.

There is also evidence to suggest that the fate of neural crest cells depends upon their migratory path in the trunk which is dictated by somites. Cells which migrate early move ventrally and pass through the anterior half sclerotome, form the sensory ganglia. Cells which are more dorsal within the anterior sclerotome form the sensory neurons and glia of the dorsal root ganglia, partly due to signals which come from the neural tube. Alternatively, the neural crest cells which migrate late travel laterally between the somite and the ectoderm, forming melanocytes in amniotes.