For an explanation, see the main splats page
The principles of the senses
- All living things have some sort of sensing ability, whether they are plant or animal, and this is reflected in their responses to changes in the environment.
- Plants demonstrate a variety of senses: a potato in a shoe box fitted with baffles demonstrates phototropism, sensing where light is coming from.
- Plants can sense the pull of gravity: radish seeds sprouting in water agar will grow downwards, and if rotated, will change the direction of growth.
- Sundews wrap their leaves around their 'prey', responding to the breakdown of prey proteins under the attack proteolytic enzymes in the sticky 'dew'.
- Sunflowers turn their flowers around to face the sun as its position in the sky changes during the day, indicating that they sense the Sun's direction somehow.
- Trigger plant flowers strike pollinating insects on the head or back when they land on the flower, either dusting them with pollen, or taking pollen from them.
- The leaves of Mimosa pudica close up when they are touched, and Cassia species close their leaves as the sun sets, indicating some equivalent of animal senses.
- A number of insectivorous plants are able to detect an insect landing on them, either using an analogue of touch or of taste as the insect is digested.
- Most animals have a sense of smell, which has the advantage of working in the dark. Smell works by a lock and key method on sensors in a small part of the nose.
- We can map taste zones on the tongue, which is able to detect salt, sweet, sour and bitter tastes on different parts, showing these have specific receptors.
- Our sense of taste is partly smell, because while the tongue can sense sweet, sour, salt and bitter, the nose can make much finer discriminations.
- Taste cells are replaced at high frequency. As cancer drugs attack fast-dividing cells, many cancer drugs can have a marked effect on the sense of taste.
- Humans hear sound within the audio frequency range, as high as 20 kilohertz, with the upper limit dropping with age, starting to drop after age 20.
- The ear captures and magnifies vibrations through the bones of the ear, and the vibrations are converted to nerve impulses that we then interpret.
- Deafness has a number of causes, such as nerve damage, blockage of the ear and damage to the amplifying mechanism in the ear. Some of these can be circumvented.
- Human hearing is selective, as shown by the cocktail party effect, where, by concentration, one person may be heard over the turmoil of a busy room.
- The pressure in our middle ear is kept steady by the Eustachian tube, which links the middle ear to the outside world. Yawning opens the Eustachian tube.
- All animals have a sense of touch: the touch sense is different from pain sense, and is only triggered by a more intense stimulus like a sharp blow.
- Hairs and whiskers can be very sensitive to touch, and this can be shown by just touching a single hair on somebody's arm or even on their head.
- Some parts of our skin are more sensitive: this can be demonstrated with a blindfold test to see where two close pressure points can be detected as separate.
- Circadian rhythms, our daily cycle of metabolic patterns, depends on detecting light and dark, so bright sunlight can help to reduce the effects of jet lag.
- The Earth has a magnetic field which experiences polar reversals at times, when the north and south poles change places over a period of a few hundred years.
- Many animals have a magnetic sense which they use in navigation: this sense must be pliable enough to cope with polar reversals, so that some of them survive.
- Many living things can detect light, usually by some chemical effect that the light causes, with the altered chemical then being detected in some way.
- The human eye detects light when rhodopsin, a complex chemical in the retina, is bleached by a focused image, produced by the lens, falling on the retina.
- There are different eye structures in different groups, indicating that the eye has evolved several times. The evidence of homeobox genes suggests otherwise.
- Most animals can either detect light or see, in the strict sense of forming an image on a receptive surface, so the image can be recognized and responded to.
- Effective vision needs a lens to focus light, a receptive surface on which the image is focused, nerves to detect the image, and a brain to analyse the image.
- There is a blind spot where the optic nerve attaches to the retina, as there are no sensors on this part of the retina. What one eye misses, the other eye sees.
- Visual perception is a brain process where a set of nervous impulses, starting in the retina and travelling along the optic nerve, are interpreted by the brain.
- We may be said to 'see' something when the brain interprets signals from the retina via the optic nerve, and recognizes them as something familiar.
- Camouflage is used by predators and prey, to get food or to avoid being food. One form of camouflage uses disruptive coloration so shapes are harder to see.
- The main parts of the vertebrate eye include the cornea, the vitreous humour, the lens, the aqueous humour, the retina and the optic nerve, and a covering.
- Visual signalling is used by animals in mate selection, and this has led to many of the weird and colourful extremes seen in the animal world.
- There are three kinds of colour receptors in the cone cells of the retina, detecting the three 'primary colours', and effectively defining the primary colours.
- The cone cells of the retina differ from the rods by having different visual photopigments so that they can respond preferentially to certain wavelengths.
- The fovea is the most sensitive part of the retina in the human eye: this is the central portion of the retina where colour vision is located as well.
- The people we call 'colour' blind can in fact see most colours. They have problems telling certain colours apart that others see as different.
- In 1794, John Dalton was the first to describe colour blindness. It was easy for him to observe this phenomenon, since he was in fact extremely blind-blind.
- Dalton believed the fluid in his eyes must be blue, and arranged for one of his eyes to be dissected, after his death, to test this. He turned out to be wrong.
- Most visual illusions are a result of conflicting signals reaching the brain, which is then required to make the best sense of them that it can.
- Some animals can detect electric fields: electric fish live in muddy water and platypuses hunt with their eyes shut, using sense organs on the 'bill'.
- In 1940, Donald Griffin and Robert Galambos announced their discovery that insectivorous bats rely on sonar echolocation to navigate and find prey.
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