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Star Nosed Mole Notes
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The Star-Nosed Mole Mole can sense underwater environment by emitting gases and sensing them back in. Member of mole family, around 50grams and found in NE USA and Canada. Lives in shallow tunnels and wetlands, hunts underground and in water. Nose has 22 fleshy appendages called RAYS. These are covered in microscopic protuberances, which are sense organs called Eimer's organs, which are sense organs containing a variety of nerve endings. There are about 25,000 Eimer's organs in the star. Eimer's organs contain a variety or nerve senses including:
1. Encapsulated corpuscle which is involved with sensing vibration
2. Merkel Cells which detect sustained pressure
3. Free nerve endings arranged in hub and spoke pattern that are important in distinguishing fine textures. So this is an animal that uses a sense of touch to locate food. The rays can manipulate objects at an extraordinary speed. For example, the rays can detect objects and move them incredibly quickly to the middle of the star. This quick method allows the mole to eat 5 pieces of prey within 1 second. Mole is one of the fastest eaters on the planet. Why eat so fast?
All to do with prey profitablility. The handling time between finding prey and eating it is very fast, so the mole can eat a lot of food in a day, making it more efficient for it to eat small prey such as earthworms, leeches, larvae and aquatic insects.
Saccades Saccades are the very rapid movements of the rays, not unlike the human eye, to move the food from the periphery of the nose to the centre. It has been suggested that the star-nose acts like an eye as it build up a tactile representation of the immediate environment.
More involved experiments have indicated that not all rays are equal. The 11th pair The 11th pair of rays are the most sensitive pair, even though they are the smallest. They are located just above the mouth. It has been suggested that the 11th pair acts a bit like the fovea of the retina, where there is the most amount of sensitivity to light information. They are the sensory fovea within the star nose. Detailed examinations to show the numbers of nerve fibres exiting the Eimer's organs have been conducted to show that from rays 1-6 the numbers are invariant but in 10 and 11 there is an increased number of nerve endings arising from the 11th pair - more capability for conducting information than the other pairs of rays. When you look at a somatosensory representation of the rays, the 11th pair, although physically the smallest, have the greatest representation. More nerve endings per Eimer's organ and more somatosensory representation. Pairs 10 and 11 have the greatest amount of cortical tissue related to the nerve endings. This is called CORTICAL MAGNIFICATION. Not surprisingly, measurements of the receptive fields of the rays show that the 11th pair has the smallest receptive field. This means that you
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