Outer and Middle Ear Anatomy and Physiology

Flashcards covering key anatomical structures, physiological functions, diagnostic tests, and clinical conditions related to the outer and middle ear, based on lecture notes.

Auricle (Pinna)

The visible part of the outer ear that funnels and directs sounds to the middle ear, assisting in sound localization.

External Acoustic Meatus (EAM)

The ear canal, a bony-cartilaginous tubular component about 4cm in length that directs sound to the tympanic membrane.

Tympanic Membrane (TM)

Also known as the eardrum, it occludes the external acoustic meatus medially and separates the outer from the middle ear, vibrating in response to sound waves.

Cerumen

A waxy oil produced by glands in the ear canal; its hardening or blockage is a common cause of temporary hearing loss.

Otitis externa

Also known as 'swimmer's ear,' it is an inflammation of the external acoustic meatus causing severe ear pain, itchiness, and discharge.

Cone of light

A normal anatomical landmark visible in the antero-inferior portion of the tympanic membrane.

Myringotomy

An incision into the tympanic membrane, often performed to drain fluid from the middle ear.

Grommets (PE tube)

Temporary ear tubes placed into the tympanic membrane to allow fluid drainage from the middle ear.

Ossicles

A chain of three small bones in the middle ear: the malleus, incus, and stapes, which convert air vibrations to fluid vibrations.

Malleus

The first ossicle in the middle ear, attached to the tympanic membrane.

Incus

The second ossicle in the middle ear, connecting the malleus and the stapes.

Stapes

The third ossicle in the middle ear, attached to the oval window.

Eustachian tube

A tube connecting the middle ear to the nasopharynx, responsible for equalizing pressure in the middle ear.

Middle Ear Function

Converts air vibrations to fluid vibrations, providing amplification of 20-30dB to match the low-impedance air with the high-impedance inner ear fluid.

Area ratio gain

An amplification mechanism in the middle ear due to the larger surface area of the tympanic membrane compared to the stapes footplate (22:1 ratio).

Lever effect

An amplification mechanism in the middle ear caused by the different lengths of the manubrium of the malleus and the long process of the incus (1.3:1 ratio).

Tensor tympani muscle

A muscle that pulls the malleus inward, increasing tension across the tympanic membrane, stiffening it to dampen chewing and talking sounds.

Acoustic reflex (Stapedius reflex)

Activated by sounds greater than 70-100dB, where the stapedius muscle retracts the stapes from the oval window to protect the cochlea, taking about 40ms to take effect.

Stapedius muscle

A muscle that retracts the stapes from the oval window as part of the acoustic reflex to protect the inner ear from loud sounds.

Weber's test

A tuning fork test where the base is placed on the forehead; lateralization of sound indicates unilateral conductive or sensorineural hearing loss.

Rinne's test

A tuning fork test comparing air conduction (AC) and bone conduction (BC); AC>BC is normal, while BC>AC indicates conductive hearing loss.

Tympanometry

An objective diagnostic procedure measuring energy transmission through the middle ear (admittance/compliance) to distinguish between sensorineural and conductive hearing loss.

Tympanogram

A graph illustrating the middle ear's response to a tone at different pressures, used to help diagnose causes of middle ear dysfunction.

Microtia

A congenital deformity where the ear (pinna) does not fully develop during pregnancy; it can range from a smaller ear to a complete absence.

Anomia

The complete absence of the external ear, classified as Type 4 Microtia, which is rarely seen.

Canal atresia (Aural atresia)

The complete absence of the ear canal, often associated with microtia.

Canal stenosis

An extremely narrow ear canal, which may be present with microtia.

Otosclerosis

Abnormal bone growth in the middle ear, most commonly affecting the stapes footplate, reducing its mobility and causing mild to severe hearing loss.

Stapedectomy

A surgical procedure to treat otosclerosis where an abnormal stapes is replaced with a prosthetic device.

Stapedotomy

A surgical procedure to treat otosclerosis involving laser adaptation of the stapes for improved movement.