Structure and Function of the Ear in Dogs
Dr. Bari Spielman
The external ear consists of the prominent earflap or pinna (also called the auricle) and the external ear canal (also called the auditory canal or meatus). The pinna is a funnel-shaped structure that collects sound and directs it into the external ear canal. The pinna is covered by skin, and the outer or posterior aspect is covered by fur. Numerous muscles are attached to the curved cartilage located between the inner and outer layers of skin around the ear, and these muscles allow the pinna to move and twitch. The external ear canal extends from the base of the pinna downward and inward towards the eardrum (also called the tympanic membrane). The external ear canal is L-shaped, with the L lying on its side. The canal forms an almost 90-degree angle between its two sections: the short, vertical outer section and the longer, horizontal inner section.
What Is the Ear?
The ears are the paired receptor organs designed for the special senses of hearing and maintaining balance. Each ear is divided anatomically and functionally into regions called the external (outside) ear, the middle ear and the inner ear.
Where Is the Ear Located?
The ears are located on both sides of the head. The external ear is identified by the visible portion of the ear, called the pinna. The pinnae of dogs vary greatly in their size and shape. The pinnae of some breeds are short and erect, while other breeds have long, floppy pinnae.
What Is the General Structure of the Ear?
The ear is divided into three portions:
The middle ear includes the eardrum and the bony tympanic cavity (osseous bulla), which lies just past the ear drum. Within this tympanic cavity are found the auditory ossicles – three tiny bones that vibrate when stimulated by sound waves. These ossicles are named the malleus, stapes and incus (commonly known as the hammer, the stirrup and the anvil because of their resemblance to these objects). These three bones form a chain across the middle ear from the tympanum to the oval window of the inner ear. The middle ear is connected to the back of the throat (pharynx) by the auditory or eustachian tube. This tube allows air from the pharynx to pass in and out of the middle ear, which helps keep middle ear pressure normal. The middle ear is connected to the inner ear through the oval window, which lies against the stapes bone.
The inner ear is located within the petrous temporal bone of the skull and consists of two parts. The osseous or bony labyrinth houses a series of thin, fluid-filled membranes called the labyrinth. The inner ear contains three distinct structures: the cochlea (spiral tube), vestibule, and three semicircular canals. The cochlea contains the nerves that transmit the electrical impulses and is directly responsible for hearing. The vestibule and semicircular canals are responsible for maintaining balance or equilibrium. These tissues are supplied by the two branches of the 8th cranial nerve (the vestiblocochlear nerve), which transmits electrical impulses related to sound and balance back to the brain.
What Are the Functions of the Ear?
The two main functions of the ear are to detect sound and allow for hearing, and to maintain balance.
Hearing. Sound first enters the external ear canal as sound waves. As these waves strike the eardrum, it begins to vibrate. These vibrations are then transmitted to the three small bones of the middle ear (the malleus, incus and stapes), which amplify the sound vibration. The end of the stapes is connected to the oval window of the inner ear. As the stapes vibrates, it transmits the sound vibrations to the cochlea, the snail shaped portion of the inner ear, which transforms the vibrations into nerve signals that are transmitted to the brain where they are interpreted as sound.
Balance. The other function of the ear is to help maintain balance. The three semicircular canals of the inner ear are oriented at right angles to each other. When the head turns, the resulting movement of fluid in these canals allows the brain to detect which way and how much the head is turning. Another part of the inner ear responds to gravity and sends information to the brain when the head is held still in a stationary position.