eye |
foot |
top 10 words in brain distribution (in article): water light form time animal type surface produce cause region |
top 10 words in brain distribution (in article): form human bone allow function size animal shape structure contain |
top 10 words in brain distribution (not in article): ice drink lamp rock wine river flow beer sea wind |
top 10 words in brain distribution (not in article): cell key lock switch body type machine muscle needle tube |
times more probable under eye 30 20 10 6 4 2.5 1.25 1 1.25 2.5 4 6 10 20 30 times more probable under foot (words not in the model) | |
Eyes'" are organs that detect light, and send signals along the optic nerve to the visual and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system. Image-resolving eyes are present in cnidaria, mollusks, chordates, annelids and arthropods. The simplest "eyes", in even unicellular organisms, do nothing but detect whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms. From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment. Overview. Complex eyes can distinguish shapes and colors. The visual fields of many organisms, especially predators, involve large areas of binocular vision to improve depth perception; in other organisms, eyes are located so as to maximise the field of view, such as in rabbits and horses. The first proto-eyes evolved among animals 540 million years ago, about the time of the so-called Cambrian explosion. The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in 6 of the thirty-something main phyla. In most vertebrates and some mollusks, the eye works by allowing light to enter it and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for color) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals for vision. The visual signals are then transmitted to the brain via the optic nerve. Such eyes are typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing lens and often an iris; the relaxing or tightening of the muscles around the iris change the size of the pupil, thereby regulating the amount of light that enters the eye, and reducing aberrations when there is enough light. The eyes of cephalopods, fish, amphibians and snakes usually have fixed lens shapes, and focusing vision is achieved by telescoping the lens — similar to how a camera focuses. Compound eyes are found among the arthropods and are composed of many simple facets which, depending on the details of anatomy, may give either a single pixelated image or multiple images, per eye. Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors, which are arranged hexagonally, and which can give a full 360-degree field of vision. Compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera, have compound eyes of only a few facets, each with a retina capable of creating an image, creating vision. With each eye viewing a different thing, a fused image from all the eyes is produced in the brain, providing very different, high-resolution images. Possessing detailed hyperspectral color vision, the Mantis shrimp has been reported to have the world's most complex color vision system. Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes. In this, they differ from most other arthropods, which have soft eyes. The number of lenses in such an eye varied, however: some trilobites had only one, and some had thousands of lenses in one eye. In contrast to compound eyes, simple eyes are those that have a single lens. | The foot is an anatomical structure found in many animals. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made up of one or more segments or bones, generally including claws or nails. General forms of the foot. An example of unguligrade feet, the hooves of a horse The feet of land vertebrates are characterized as either plantigrade, digitigrade, or unguligrade. In plantigrade animals, such as humans, frogs or bears, the bottom of the entire foot supports the weight of the animal. In digitigrade animals, such as cats, wolves or birds, the toes bear the animal's weight, while the upper regions of the foot, the ankle and wrist, remain elevated. Finally, in unguligrade animals, such as cows or horses, even the toes are elevated, the animal standing only atop its nails, which have evolved to bear weight and are called hooves. Anatomy. The human foot is of the plantigrade form. The major bones in the human foot are: The foot also contains sesamoid bones in distal portion of the first metatarsal bone. Anthropometry. An anthropometric study of 1197 North American adult Caucasian males (mean age 35.5 years) found that mean foot length was 26.3 cm with a standard deviation of 1.2 cm. In culture. Worldwide, different cultures treat and perceive feet very differently: Footwear customs. Customs about footwear while indoors vary significantly from place to place and usually depend on climate, weather, and other factors: Customary measurement. One way to measure short distances on the ground is by placing one foot directly in front of the other; this led to the adoption of the foot as a unit of length, even though not all human feet correspond to this measure. Myths. It is a myth that the Imperial "foot" (304.8 mm) is about the length of the average European male foot. The average today is less than 280 mm and 90% of the population is within 20 mm of that. Although many men today have feet that are 11.5 inches long (size 12-13): most are less than size 11. In the past, the average length would have been even less. The overall length of most shoes however, is above one "foot". Tradition has it that the Imperial foot was based upon the size of Hercules' foot or the size of the king of England. Medical aspects. Due to their position and function, feet are exposed to a variety of potential infections and injuries, including athlete's foot, bunions, ingrown toenails, Morton's neuroma, plantar fasciitis, plantar warts and stress fractures. In addition, there are several genetic conditions that can affect the shape and function of the feet, including a club foot or flat feet. This leaves humans more vulnerable to medical problems that are caused by poor leg and foot alignments. Also, the wearing of shoes, sneakers and boots can impede proper alignment and movement within the ankle and foot. For example, high heels are known to throw off the natural weight balance (this can also affect the lower back). For the sake of posture, flat soles and heels are advised. A doctor who specializes in the treatment of the feet practices podiatry and is called a podiatrist. A pedorthist specializes in the use and modification of footwear to treat problems related to the lower limbs. |