Canines have excellent hearing, partially due to the L-shape of their ear canal which helps protect the ear drum. This structure also makes it harder for wax or foreign substances to leave the ear naturally and can result in hearing difficulties, even deafness. Certain breeds are genetically predisposed to hearing problems, and others' excessive amounts of hair also makes them more likely to develop ear maladies.
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Anatomy
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The structure of a dog's ear is complex. A dog's ear is divided into the external ear, middle ear and inner ear. The external ear includes the visible earflap (pinna) which funnels sound into the ear canal. This canal ends at the middle ear's eardrum and is connected to the throat by the eustachian tube. Inside the inner ear, a bony web of fluid-filled canals helps the dog maintain balance while the spiral-shaped cochlea transmits nerve impulses essential to hearing.
Function
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Canine hearing is acute. Sound waves enter the external ear canal and cause the eardrum to vibrate. These vibrations travel to the middle ear and strike the malleus, inclus and stapes bones, which in turn amplify the sound. As the stapes vibrates, the sound is directed to the inner ear's cochlea, which in turn transforms the vibrations into nerve signals. These signals go to the brain and are translated into sound.
Ears and Balance
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The inner ear helps a dog maintain balance. When a dog turns its head, fluids shift in the canals of the inner ears. The brain detects this shifting and identifies the range of motion of the head. Signals received from other parts of the inner ear respond to gravity and allow the dog to maintain equilibrium.
Hearing Development
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Puppies are born unable to hear. All puppies are born unable to hear even the loudest noises because their ear canals are closed until they are about 10 days old. At the age of three weeks, puppy's ear canals open fully and they are able to hear most sounds. Complete hearing becomes possible at about 21 days. Prior to this time, it is difficult to test for hearing impairment.
Causes of Deafness
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Excessive hair can cause ear problems. Some dogs are born deaf, due to genetics or a structural problem. Excessive ear wax can cause temporary hearing loss, especially in breeds with narrow ear canals, such as poodles. If a dog has a lot of hair around its ear, the ear canal can get blocked. A foreign object such as a toy or stick that becomes lodged in a dog's ear also can reduce hearing. Aging, a bad reaction to a drug, injury or serious ear infections can cause permanent hearing damage.
Considerations
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Some breeds are prone to deafness. According to the ASPCA, the Dalmation is the breed most associated with inherited deafness. In addition, the beagle, bull terrier, English bulldog and English setter have a higher likelihood of developing deafness than other breeds. Some breeds with merle coloring, such as the Australian sheperd, rough collie, Shetland sheepdog and harlequin great dane, also show a higher risk. Deaf dogs can be taught to react to hand signals.
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