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Anatomy of the Ear and Types of Hearing Loss


The ear is divided into three portions: the external, middle and inner ear.  The external ear consists of the auricle which gathers sound and funnels it through a tube known as external auditory canal (acoustic meatus) to the tympanic membrane (ear drum). The tympanic membrane is attached to three tiny bones (ossicles): maleus, incus and stapes. The membrane and the tiny bones make up the middle ear. The inner ear consists of the cochlea, vestibule, and semicircular canals. The cochlea contains a spiral organ of corti and a basilar membrane with hair cells.

Sound, which travels in waves similar to light, enters the ear through the external auditory canal and strikes the tympanic membrane causing the bones attached to it to vibrate. As these bones vibrate, a structure called the oval window moves in and out, transmitting the vibrations to the fluid inside the cochlea. The hair cells inside the cochlea receive the fluid vibrations of sound and transduce them into electrical impulses that are carried to the brain by sensory nerves.

hearing loss Anatomy of the Ear and Types of Hearing Loss

There are two types of hearing losses: conductive and sensori-neural. In order to diagnose either of these, the Webber or Rinne test must be performed.

In the Webber test, the tuning fork is struck and placed on the middle of the patient’s forehead or on top of the patient’s head equally distant from both ears.  The patient is then asked to determine which ear the sound is heard best at. A normal Webber test is when the patient is able to hear the sound equally on both ears.

In the Rinne test, the tuning fork is struck and placed on the patient’s mastoid process and asked when the patient can no longer hear it, after which the tuning fork is moved just outside the external auditory meatus, and the patient is asked again when the sound can no longer be heard. A normal Rinne test is when the patient can hear the sound for much longer through air than when placed on the mastoid process. This test basically points whether the patient has a sensorineural hearing loss or a conductive hearing loss. To determine the ear affected, the webber test is done.

In conductive hearing loss, the patient will have an abnormal Rinne test with bone conduction greater than air conduction. The patient’s Webber test will show the patient to have sound lateralize to the affected ear.

In sensorineural hearing loss, the patient will have a normal Rinne test with air conduction greater than bone conduction. The patient’s Webber test will show the patient to have sound lateralize to the unaffected ear.

Examples:

Rinne Left BC>AC & Weber’s lateralized to the left = conductive loss on the left
Rinne Right BC>AC & Weber’s lateralized to the right = conductive loss on the right

Weber Lateralizes Left & Rinne both ears AC > BC = senorinerual loss Right ear
Weber Lateralizes Right & Rinne both ears AC > BC = sensorineural loss Left ear

Article by: Ahlaam Mahmood

Tags: Rinne test, Weber test


Last updated: March 10, 2013



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