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the human eye

human eye

The three nerves that control eye movement and pupil diameter are:

  1. Oculomotor Nerve
  2. Trochlear Nerve
  3. Abducens Nerve

The human eye is equipped with a variety of optical components including the cornea, iris, pupil, aqueous and vitreous humors, a variable-focus lens, and the retina (as illustrated in Figure 1). Together, these elements work to form images of the objects that fall into the field of view for each eye. When an object is observed, it is first focused through the convex cornea and lens elements, forming an inverted image on the surface of the retina, a multi-layered membrane that contains millions of light-sensitive cells. In order to reach the retina, light rays focused by the cornea must successively traverse the aqueous humor (in the anterior chamber), the crystalline lens, the gelatinous vitreous body, and the vascular and neuronal layers of the retina before they reach the photosensitive outer segments of the cone and rod cells. These photosensory cells detect the image and translate it into a series of electrical signals for transmission to the brain.

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Humans have three brains

human brainBy James Thornton

The brain is our favorite bodily organ. It is where we feel sex, love, and beauty. It is where we get guilty, depressed, and angry. It is the most complex object in the known Universe. So complex that science has only made the first tentative steps towards understanding it.

One thing is clear though: you have three brains. There are three brains nested within your skull: the lizard brain, the dog brain, and the human brain.

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What is swine flu?

Image Q: This super-virus we’re looking at now is said to be a cross between a pig flu, a human flu and also the bird flu, which has been deadly too. Does this make it even more dangerous?

Dr Smith: Flu is broken down into a number of different types: there’s flu A, flu B and flu C. Flu A is the bird form and, of course, humans also have a flu A. Then we further categorise it according to the surface molecules, the H (for Haemagglutinin) and the N on the surface.

This new strain is a H1N1 virus, which we know circulates in humans, pigs and birds. It’s possible that the pig initially got some of its flu from a bird and then co-mixed that with the human form to produce this hybrid, which is why you can find elements of all three.

It is very much early days and the big focus now, through infection control organisations like the Centres for Disease and Prevention (CDP) and the WHO, will be to interrogate this virus at a molecular level.

In other words, look at the genetic make-up, sequence the virus, and once they’ve got the genetic sequence you can begin to unpick where it’s come from, what its origins are, and therefore begin to build the story as to what its likely outcome will be.

Q: What do we know about the swine flu virus in general and what do we know about this new strain?

Dr Chris Smith: The flu is a very ancestrally old illness. It’s a virus that has been around for thousands of years. It started off as an infection in birds and slowly over those thousands of years diversified to infect every single warm-blooded animal on Earth and a few cold-blooded ones, including snakes.

All these different organisms have their own forms of flu and periodically they can exchange them with other related animals. Birds can exchange their forms of flu with us, that gives us bird flu and periodically spawns one type of pandemic. Also, pigs can exchange their form of flu with birds and perhaps other large mammals, including horses. Because pigs, as very big mammals, are so similar to humans, they can also exchange viruses with humans and this is why we think the present outbreak could have occurred.

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