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Animal Behavi25 - shape of the pigment molecules This...

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Animal Behavior: Instinct Thermoreception Thermoreception, the detection of temperature changes, is present in most animals, but has been little studied. Many insects have temperature-sensitive nerve endings, either on their legs to detect ground temperature, or on their antennae to detect air temperature. Fish have thermoreceptors on the skin, lateral line (which also detects electrical signals and vibrations), and in the brain. Birds are not known to have many thermoreceptors in the skin, but have them on the tongue and bill in some species. Mammals have distinct heat and cold receptors distributed throughout the skin. There are also thermoreceptors deep within the body that can cause shivering even when skin and brain receptors are detecting a constant temperature. Thermoreceptors in the spinal cord can influence shivering, panting, and changes in blood flow. Photoreceptors and Vision Photoreceptors cells contain a pigment that is sensitive to light. Light reversibly changes the
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Unformatted text preview: shape of the pigment molecules. This process leads to electrical changes in the receptor membrane that in turn lead to the propagation of a nerve signal. In some animals, such as the earthworm, photoreceptors are scattered over the skin. Usually, however, photoreceptors are clustered together to form an eye. Primitive eyes detect only the presence or absence of light. In the more advanced vertebrate eye, there are two types of receptors: rods and cones. Rods are elongated and sensitive to low levels of illumination. This vision is colorless and has poor definition. Rods are predominant in nocturnal animals, for which increased sensitivity is important. Cones are sensitive to high levels of illumination and produce a sharp picture. Unlike rods, cones contain more than one type of photopigment, each sensitive to different wavelengths of light. Cones provide color vision....
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