Physical Fitness and Well-Being and Eye Care Part 1

About physical fitness, medical information, trivia, anatomy, well-being and care of your eyes.

TAKING A PHYSICAL--HEAD TO TOE

EYES

Your eyes are the sensory organs of light and color. Each eye is lined with light-sensitive cells which send signals to the optic nerve of your brain.

When you look at an object, the image of that object appears upside down on your retina. However, your brain automatically corrects for this, allowing you to perceive the object right side up.

Experiments have been done in which people wore devices which caused them to perceive the world upside down. Within two days, however, their brains were automatically making corrections, and they reported that everything seemed right side up again.

After removal of the experimental devices, normal vision appeared to be upside down to the people in the experiment. Once more they went through a period of readjustment, until the world looked right side up once more.

In most cases, the right half of your brain serves the left side of your body, and vice versa. This is different for your eyes. The left side of your left eye is served by the left half of your brain, and the right side of your left eye is served by the right half of your brain. The same pattern, in reverse, occurs for your right eye. Thus, each half of your brain receives a composite of signals from both eyes at once.

Basically, there are six parts to each eye:

1. Eyeball: holds the working parts of the eyes and allows them to move in a variety of directions, without your having to move your head.

2. Lens: focuses light, reflected from images in the outside world, to light-sensitive cells in your eyeball.

3. Retina: a membrane of light-sensitive cells inside your eyeball.

4. Iris: controls the amount of light entering your eyeball.

5. Muscles: turn your eyeball.

6. Optic nerve: a sensory cranial nerve that carries visual stimuli from the retina to the brain.

The light-sensitive cells on the inside of your eyes are of two types: rods, which are sensitive to light but not to color; and cones, which are color-sensitive.

Rods and cones are nerve cells, connected to the optic nerve by nerve fibers.

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