Photoreceptor Damage: Causes and Possibilities
Over 10,000,000 people around the world suffer from some sort of blindness or handicap due to photoreceptor damage. These effects can be caused by a number of afflictions, including retinitis pigmentosa, macular degeneration, and tumors. These illnesses vary in severity from being a mere hindrance to completely blinding the individual. Until recently, those affected were left without hope of a cure or even a treatment that would somewhat improve their vision. But over the last few years, several groups of scientists have been working on a partial cure in the form of neuroprostheses, artificial devices which are inserted in the eye behind or on top of the damaged retinal area. These photoreceptive chips, in theory, should provide information too the healthy neurons residing in the retina, substituting for the damaged photoreceptors.
When we open our eyes, millions of tiny events occur that allow us to see. Our pupils automatically constrict in accordance to the light level, the variable lens bends and adjusts to fit the distance of what we are looking, and our photoreceptors receive information in accordance to the previous factors. (This is extremely simplified, but it will suffice for now.) Photoreceptors are tiny, specialized neurons located in the retina at the back of the eye. There are two types of photoreceptors, rods and cones. Each follow the same principles: when light hits them they respond with a chemical reaction using a substance known as rhodopsin. Once this reaction occurs a chain of events sends this message down a number of sophisticated and specialized neurons, eventually reaching the brain and resulting in what we call sight.
Rods (numbering one hundred million or so in each eye) are primarily in the periphery of our visual field. They are extremely sensitive to light and are often ÒtiedÓ together on a lower level to allow for greater sensitivity. Rods do not see in with good resolution and cannot differentiate colors.
Cones (only five million or so exist) are mostly found on the center of the visual field, a place called the fovea. The words you are reading now are being processed by cones in the fovea. They operate in brighter light than rods and detect color (there are three types, each responding to a particular range of wavelengths). Cones do not pool their output and exist for resolution, not mere detection. The only drawback with the cone system is the amount of light saturation necessary to stimulate them and send their signal to the brain.
Europe, in the late 1800’s, was starting for a land grab in the African continent. Around 1878, most of Africa was unexplored, but by 1914, most of Africa, with the lucky exception of Liberia and Ethiopia, was carved up between European powers. There were countless motivations that spurred the European powers to carve Africa, like economical, political, and socio–cultural, and there were countless attitudes towards this expansion into Africa, some of approval and some of condemnation.
Imperialism in Africa took root in the late 19th century when European nations divided up the continent for their own benefit. Each nation practiced a certain type of rule over the Africans of which they conquered. For example, the Germans, the Dutch, and the French used the practice of Direct Rule over their colonies in Africa. This system is characterized by the colonizers need for the colonized to become assimilated into their culture. The purpose of this was to make the African people “civilized” and act like Europeans. The governing administrations forced on the native inhabitants by the colonial power were meant to undermine those institutions set in place by the indigenous people. By taking over the community’s government on all levels,
In the modern day, Africa is seen by the world around it as a relatively underprivileged continent. Since its independence from colonial rule, Africa 's economic performance has been less than stellar and its advancement has been slow, which could be argued through a myriad of different ideologies. Nathan Nunn, the author of “Historical Legacies: A model linking Africa’s past to its current underdevelopment” believes that the slave trade and colonial rule, brought on by the Europeans in the past, is the reason for Africa’s economic hardships, that are still lingering to this day. What he sets out to answer in this academic paper is an interesting question, “Why do these events, which ended years ago, continue to matter today?” Through the
New Imperialism began in the last quarter of the nineteenth century and was a time when European powers began to pursue a structured (more formal) political control over other areas. Yet it is important to keep in mind that informal empires tend to have an expiration date. As time progresses, history shows us that one of the parties involved will start pushing for change, whether that change is for power or independence is based on the side that provoked the change. In this case, the party that pushed for change was the superior one. The push for power was motivated by greed and an overwhelming desire to control every aspect of valuable foreign areas. One of the biggest moments in the history of colonization was the ‘Scramble for Africa’, as historians (and Professor Hopkins) refer to it as. As slaves were the biggest resource of the time, the banning of slave trade in Africa in the early nineteenth century caused European disinterest in continent that they were once heavily dependent on. Although there were localized replacements, like ivory trading, they were not as effective in keeping Europe’s interest. As a result, Africa was desperate to be relevant again, their economy depended on it. Because of the ban on the slave trade, there was a sudden demographic collapse of middle aged persons, which was also counterproductive to the growth of the continent. Before the scramble, Africa was naturally
In the late nineteenth century, early twentieth century, western nations wanted to expand their territory. After the industrial revolution provided western Nations wealth and technology that could be used to take over less advanced societies. European powers proceeded on building empires in Africa. They found Africa to be home of many valuable natural resources they needed to fuel they industries, and supply cheap raw materials for factories. They wanted new markets where they could trade good produce by factories, and a place to invest profits. European Nations also wanted to spread Christianity, and though themselves to be superior. Meanwhile, powerful industrialized European countries wanted to gain powers by building overseas Empires. Through economic and military powers, European was able to colonize, and dominate Africa. European Imperialism had a negative impact on African’s culture; environment and was racist to African while trying to make them adapt to western manners.
The way countries, nations or states act and base their policies on many times reflect what their past was like. This is very true in the case of Africa. The only problem is that Africa is said to have no history. This just means that Africa’s many cultures did not affect the way imperialists and other influences acted towards the huge continent. Everything was based on their interests and consequently this meant that the way of dealing with Africa in every way was based on Western traditionalists. To this we must answer the question how has the Western World affected Africa’s present stage and what must be done to undo what is wrong and hopefully correct this situation.
In order to lead and set direction, a leader needs to appear confident as a person and in the leadership role. Upon arrival, when the boys were appointing a leader, without hesitation, saw that "there was a stillness about Ralph as he sat that marked him out… most obscurely, yet most powerfully, there was the conch… The being that had blown that… was set apart" (22). This quote reveals that although one can have a great vision and good ideas regarding the change, if one is not confident, then the action will not occur. Without action, there is no change. With this being said, Ralph knew that they had to take action considering that if they did nothing, the predicament would remain the same and then proceeded to blow the conch to signal for any fellow survivors. Ralph’s connection with the conch allows him to appear confident in the eyes of the littluns since the conch is what brought them all together. It was as if a hidden personality within Ralph had taken control saying, “‘I’m chief. I’ll go. Don’t argue’”(104). Ralph is not the one agreeing to go look for the beast; it is the chief inside of him. He knows that the littluns are depending on him to guide them, and he takes that responsibility into consideration when making it
Ralph is undoubtedly the most well rounded leader on the entire island. He shows courage and confidence, both of which are key characteristics of a great leader. An excellent example of Ralph’s courage appears when the boys venture out in search of the beast into unknown parts of the island. "His mouth was tight and pale. He put back his hair very slowly.....He forced his feet to move until they carried him out on to the neck of the land" (Golding 130). Ralph instinctively knows that as a leader he must physically take charge of the search party, despite his feelings of fear. Another small situation were Ralph shows courage is when he steps in between 2 people arguing and takes control of the situation. “Ralph pushed between them and got a thump on the chest.” (Golding 90). Alongside courage, Ralph also exhibits confidence in his role of leadership. Throughout the novel, Ralph consistently says what needs to be done with confidence. In chapter 2, Ralph lays down the rules and what must be done to survive. “If we have a signal going, they’ll come…And another thing. We ...
Now for our eyes we use them for vision, their like our own personal camera’s,
retina. The image that forms on your retina is flat, but you see a world of
Color Vision Development in Infants: The Responsibility of Cone Types and Wavelength in Order of Color Development
In terms of political changes, European imperialism negatively affected Africa. Firstly, European colonization created enormous conflict between colonists and the African people. African resistance to “The Scramble for Africa” lead to the instability of Africa’s political structure. There was ineffective resistance of the African people against the Europeans. In an attempt to regain their independence, Africans took up arms against their colonial masters as soon as they perceived them to be at a disadvantage. In southern Africa, in The Republic of Namibia, the Herero people rose against German rule in 1904, killing over 100 German settlers and traders. German commander, General von Trotha, retaliated with a war aimed simply at extermination. This resulted in the decline of 70% of the Herero population.1 Nowhere else was colonialism quite so brutal, but almost everywhere it tended towards unrestrained brutality as soon as it was challenged.2 Warfare created considerable unrest among African people. Afterwards, the people of Africa came to the realization that the consequences of resistance against European colonists could be devastating. As well, the Europeans demonstrated that they had the technology and resources to gain control. Secondly, colonial expansion changed the face of Africa’s political structure. The Berlin Conference of 1884-85, attended by 13 European nations and the USA, set the ground rules for partition of Africa. When the conferenc...
Africa has had a long and tumultuous road of colonization and decolonization the rush to colonize Africa started in the 17th century with the discovery of the vast amounts of gold, diamonds, and rubber with colonization hitting a fever pitch during World War I. However, the repercussions of colonization have left deep wounds that still remain unhealed in the 21st century. Early on, European nations such as Britain, Portugal, Spain, Italy, Germany and Belgium scrambled for territories. Countries wanted land so they could harvest the resources, increase trade, and gain power. The European colonization of Africa brought racism, civil unrest, and insatiable greed; all of which have had lasting impacts on Africa.
Visual perception and visual sensation are both interactive processes, although there is a significant difference between the two processes. Sensation is defined as the stimulation of sense organs Visual sensation is a physiological process which means that it is the same for everyone. We absorb energy such as electro magnetic energy (light) or sound waves by sensory organs such as eyes. This energy is then transduced into electro chemical energy by the cones and rods (receptor cells) in the retina. There are four main stages of sensation. Sensation involves detection of stimuli incoming from the surrounding world, registering of the stimulus by the receptor cells, transduction or changing of the stimulus energy to an electric nerve impulse, and then finally the transmission of that electrical impulse into the brain. Our brain then perceives what the information is. Hence perception is defined as the selection, organisation and interpretation of that sensory input.
This reflected light passes through the lens and falls on to the retina of the eye. Here, the light induces nerve impulses that travel through the optic nerve to the brain, where it makes an image of the object, and then that image is passed on to muscles and glands.The eye is well protected. It lies within a bony socket of the skull. The eyelids guard it in front. They blink an average of once every six seconds. This washes the eye with the salty secretion from the tear, or lachrymal, glands.