Audiology Chapters 8, 9, 10

Structures & Function of Outer Ear

Auricle (or pinna), the external auditory canal, and the tympanic membrane

- Gathers sound/sound waves from the environment and funnels them into the auditory canal towards the middle ear

Auricle—Structure & Function

The outermost, visible part of the ear, also referred to as the pinna

- Its funnel shape gathers sound waves from the environment

- Funnels sound into the external ear canal

- Enhances delivery of high-frequency sounds relative to low-frequency sounds

- Aids localization

External Auditory Canal (EAC)

Also referred to as the external auditory meatus (EAM)

- Forms at the concha and extends inward at a slight upward angle

- In small children, it angles downward

Functions of EAC

- Protects the tympanic membrane (TM) from trauma and foreign objects

- Keeps TM at constant temperature and humidity levels

- Serves as a sound filter

- Reduces low frequencies

- Resonator for frequencies between 2K and 7K Hz

Tympanic Membrane

The concave, disk-like structure at the end of the external auditory canal, commonly referred to as the eardrum.

How can you view the Tympanic Membrane?

It is necessary to observe the TM with direct light, such as that from an otoscope

TM is semi-transparent; visible via an otoscope

Disorders of the Outer Ear

Conductive Hearing Loss

When conditions occur that interfere with or block the normal sound vibrations transmitted through the outer ear

External Otitis

Commonly referred to as “swimmer’s ear,” it is an infection that occurs in the skin of the external auditory canal

Atresia

Congenital malformation of the external ear canal

Lack of canalization

Stenosis

Narrowing of the EAC

Does not directly cause a hearing loss but can be easily clogged by earwax/debris

Foreign Bodies

Collapsed auditory canals

Osteomas: benign bone tumors that arise in any region of the bony EAC

Exostoses: benign, bony growths covered by skin

Cerumen impaction: An accumulation of wax that can affect the flow of sound to the tympanic membrane

Ruptured or Perforated Tympanic Membrane

Tympanosclerosis is a thickening and scarring of the TM

Structures & Function of the Middle Ear

- The middle ear (or tympanic cavity) includes the middle ear bones (ossicles), middle ear muscles and ligaments, and the eustachian tube

The middle ear carries vibrations from the outer ear to the inner ear by transferring the sound energy from the air in the outer ear to the fluid of the inner ear.

The middle ear is separated from the outer ear by the tympanic membrane (eardrum).

Ossicular Chain/Ossicles Structures & Functions

Smallest bones in the human body, 2-6 mm long, suspended in the middle ear via ligaments

- Malleus

- Incus

- Staples

- To carry tympanic membrane vibrations to the inner ear

- Lever action of the ossicular chain adds to signal intensity to overcome the impedance mismatch of the middle and inner ear

Stapes

The smallest bone in the body

Footplate/base

- Fits into the oval window

Eustachian Tube

The eustachian tube enters the middle ear anteriorly and passes down into the nasopharynx.

- In adults: It sits at approx. a 30 degree angle and is 35-38 mm in length.

- In infants: It is shorter and wider in relation to its length and positioned more horizontally.

Purpose is to equalize the pressure in the middle ear to the outside world and hence to that of the external auditory canal in order to maximize sound transmission

Mastoid Bone

The portion of the temporal bone of the skull that surrounds the ear, containing open, air-containing spaces.

Mastoid Process

The bony protuberance behind the auricle.

Oval Window

A membrane covering connecting the middle ear space to the inner ear, supporting the base of the stapes.

Round Window

A membrane that vibrates in opposite phase to vibrations entering the inner ear through the oval window, allowing fluid in the cochlea to move.

Disorders of the Middle Ear

Eustachian Tube Dysfunction: Due to narrowing or obstruction, it may lead to chronic Negative middle ear pressure

Otitis Media: It is an infection of the mucous membrane lining in the middle ear due to bacteria or a virus

Cholesteatoma: A growth of epidermal and connective tissue in the spaces of the middle ear.

Otosclerosis: A bony growth around the point of insertion of the stapes into the cochlea (oval window).

Mastoiditis: A bacterial infection of the mastoid air cells surrounding the inner and middle ear, often as a result of an unresolved middle ear infection (otitis media)

Patulous Eustachian Tube: Eustachian tube is chronically open

Inner Ear Function

- The inner ear transduces mechanical energy from the middle ear to electrochemical energy (neural messages) that is processed in the brain

- The inner ear processes information regarding the body's position and movement

Two portions of Inner Ear

Vestibular (balance) portion

Houses organs of equilibrium

Cochlear (auditory) portion

Organ of hearing

Equilibrium

The ability to maintain our balance depends on information from several body systems that provide the brain with visual, proprioceptive, and vestibular inpu

Sensorineural hearing loss (SNHL)

- Account for the largest group of hearing losses.

- Most originate with sensory loss caused by damage of the hair cells

- Neural loss caused by damage of the auditory nerve

- Major complaint frequently is not being able to understand what is being said

Disorders of Inner Ear

Viral or Bacterial Infections

Ototoxic Hearing Loss: Hearing loss caused by exposure to drugs or chemicals that are toxic (poisonous) to the inner ear (specifically to the cochlea or auditory nerve and sometimes the vestibular system)

Noise-induced hearing loss: Hearing loss due to noise exposure

Presbycusis: Hearing loss due to aging

Meniere’s Disease: A disorder of the labyrinth of the inner ear and is characterized by sudden attacks of vertigo, tinnitus, vomiting, and hearing loss.

Sudden Idiopathic Sensory/Neural Hearing Loss (SISNHL): Hearing loss, usually unilateral, that develops instantly or over the course of a few days

Autoimmune Inner-Ear Disease (AIED): Results in bilateral, fluctuating, progressive sensory hearing loss

Semicircular Canal Dehiscence Syndrome (SCDS): Due to weakening of the bone that covers the semicircular canals, which can cause a third window in the inner ear

Sensorineural Hearing Loss (SNHL)

Accounts for the largest group of hearing losses, often originating from sensory loss caused by damage to hair cells.

Classifying Different Types of Hearing Loss

Congenital/Prenatal: Occurring before birth

- Hereditary/Genetic

- Maternal infection/disease while pregnant

- Malformation of the inner ear

- Anoxia

- Rh factor

- Thalidomide

Perinatal: Occurring during birth

- Anoxia

- Exposure to virus from infected mother during birth

- Trauma to fetal head

- Prematurity

Acquired/Postnatal: Occurring after birth

- Disease/illness causing hearing loss

- Tobacco Smoke Exposure

- Barotrauma

- Radiation exposure

- Head Trauma

- Aging

When describing an audiogram, you must include

Ear-specific: unilateral or bilateral

Degree: mild, moderate, severe

Type: conductive, mixed, sensorineural