Dog Owner's Home Veterinary Handbook.pdf - Mr. Walnuts

C h a p t e r
THE EARS
Hearing is one of the dog’s keenest senses. Dogs can hear sounds too faint for
us to detect, and can also hear noises pitched at a much higher frequency.
They can detect very slight changes in tones of sounds much better than we
can. Because their hearing is so acute, dogs rely much more on their hearing
than on their eyesight to navigate the world.
Dogs’ ears come in all sizes and shapes, and can be carried erect, bent, or
flopped over. The outside of the ear flap is covered by hair that matches the
rest of the coat. Hair is also present on the inside of the ear flap, although it is
sparsely distributed in most breeds. Some breeds, such as Cocker Spaniels and
Poodles, will have a great deal of hair both on the flap and down into the ear
canal. The skin on the inside of the ear flap is light pink in some breeds and
spotted in others.
Sound, which is really vibrations of the air, is collected by the ear flap, or
pinna, and directed down the comparatively large ear canal. (In puppies,
there is no opening to the ear canal until some time between 1 and 2 weeks of
age, so they are virtually deaf until then.) The ear canal descends in a vertical
direction and then angles horizontally to end at the eardrum (tympanic membrane).
This shape is the cause of many ear problems, since moisture or debris
that goes into the ear is often trapped down there. Movements of the tympanic
membrane are transmitted via a chain of small bones (the auditory ossicles)
to the bony canals of the inner ear.
Within the bony canals lies the cochlea. The cochlea, which is the receptor
organ for hearing, contains a lymphlike fluid that converts sound vibrations
into fluid waves. The fluid waves are transformed into nerve impulses
and conducted by the cochlear nerve to the auditory nerve.
Within the bony canals also lies the vestibular apparatus, an organ of balance
composed of the semicircular canals, the utricle, and the saccule. The
purpose of the vestibular apparatus is to synchronize eye movements and
maintain posture, balance, and coordination. The vestibular nerve joins the
cochlear nerve to form the auditory nerve that connects to the hearing and
balance centers in the brain.
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