The ear's most noted function is, of course, hearing. The ear also has a lesser known but just as important role in a dog's sense of balance or equilibrium.
Ear Anatomy
Simply, the ear can be divided into the outer ear, middle ear, and inner ear. Each area has a specific function that allows for hearing or balance.
Pinna
Some dogs have ear flaps, or pinnas, that stand erect, while others have long, floppy ear flaps. The ear flap serves as a partial covering of the ear canal, while at the same time directing sound towards the eardrum. The flap has an inner core of cartilage to give it strength. The pinna has more than twenty muscles that give it 180 degrees of motion to collect and funnel sounds to the eardrum. Both outer and inner surfaces of the skin are covered by hair, although hair follicles are much less prevalent on the inner areas.
Ear Canal
The ear canal is a long, tube-like structure that travels diagonally down the side of the head, then moves horizontally into the head. The total length of the ear canal is at least two inches, even in small breeds. It is about as wide as a pencil. The length and size of the canal vary in relation to the animal's overall body size. As the ear canal passes into the head, it ends at a thin tissue called the tympanic membrane or eardrum.
Outer Ear
The outer ear in the dog is considered to include all structures, such as the ear canal and ear flap, from the eardrum outward.
Middle Ear
Internally, from the eardrum comes the middle ear, which connects to the back of the throat area by the eustachian tube. This tube allows air to enter the middle ear to balance or equalize the pressure against the eardrum. The middle ear also contains three bones (the hammer, anvil, and stirrup) which are involved in hearing.
Inner Ear
Farther in from the middle ear is the inner ear. One responsibility of the inner ear is the maintenance of the dog's equilibrium or balance. This structure contains fluid-filled canals, called the semicircular canals. When the fluid shifts within the semicircular canals, it tells the brain the body's exact position. If a dog's head is tilted the fluid shifts, and the brain detects the tilting.
Eardrum
The eardrum picks up sound waves through air vibration. The eardrum vibrates and stimulates the bones within the middle ear. The vibrating bones pass the sound vibrations to an area with tiny hairs. As the hair moves, sound waves are transformed to electrical impulses and then passed to the inner ear where they are transmitted by the auditory nerve to the brain where they are detected as sound. This is how hearing is created.
The parts of the ear, namely the ear flap, ear canal, eardrum, and middle and inner ears, all play important roles. These structures are complex and can become diseased, thus impairing their function. Disorders of the ear are frequently very painful and can affect both hearing and equilibrium.
Hearing Development
Puppies are born unable to hear. They are unresponsive to even loud noises. The ear canals described above remain closed, unable to carry sound to the eardrum until the puppy is about ten days of age. In some individuals, the ear canals may open slightly sooner or later but it averages about ten days. The canals become fully open by three weeks of age. As a result of the ear canals 'opening up,' most puppies will begin to hear sounds at about fourteen days of age, with functional hearing by twenty-one days of age. It is very difficult to assess possible hearing impairment until the puppy is at least four weeks of age, at which time deafness, if present, may be noticed and evaluated.
Article by: Race Foster, DVM and Angela Walter, DVM