a&p hearing mech exam 2

What are the four other names for the middle ear?

• Middle ear cavity • Tympanum • Mesotympanum • Cavum tympanicum

What are the approximate dimensions of the average adult middle ear?

• About 1/2 in high • About 1/2 in wide • About 1/4 in deep • Air-filled space

What type of tissue lines the middle ear?

Mucus membrane

What are the contents of the middle ear?

• Ossicles • Tensor tympani muscle • Stapedius muscle • Connective tissue

What shape model is used to picture the middle ear cavity?

A box with 6 walls

What structure forms the lateral wall of the middle ear, and what does it divide?

• Tympanic membrane (TM) • Divides the outer ear from the middle ear

What is the shape of the tympanic membrane?

Concave, disc-like structure of fibrous tissue

How many layers make up the tympanic membrane?

3

Name the tissue of each TM layer, lateral to medial.

• Lateral: epithelium • Middle: fibrous connective tissue • Medial: mucus membrane

How are the fibers of the middle TM layer arranged?

• Circumferential concentric rings • Radial spoke-like fibers

Which TM landmark marks the point of inward displacement (about 2 mm)?

Umbo

What is the thickening around the TM that fits into the tympanic sulcus?

Annulus

What is the pars flaccida also called?

Shrapnell's membrane

In what space on the TM does negative pressure occur first?

Prussak's space

List the major landmarks of the tympanic membrane.

• Manubrium • Cone of light • Long process of incus • Umbo • Annulus • Pars tensa • Pars flaccida (Shrapnell's membrane) • Prussak's space

What are the 4 quadrants of the tympanic membrane?

• Anterior inferior • Anterior superior • Posterior inferior • Posterior superior

What causes the cone of light seen on the TM?

Reflex of the otoscope light

Right ear: clock positions of the manubrium and cone of light?

• Manubrium: 1:00 • Cone of light: 5:00

Left ear: clock positions of the manubrium and cone of light?

• Manubrium: 11:00 • Cone of light: 7:00

What 4 structures are on the medial wall of the middle ear?

• Promontory • Oval window • Round window • Fallopian canal

What is the promontory?

• Bony protrusion caused by the basal turn of the cochlea • Extends into the ME space • Separates the oval and round windows

Which medial wall aperture sits beneath the footplate of the stapes?

Oval window

Which medial wall aperture contains a thin, rough membrane?

Round window

What separates the oval window from the round window?

The promontory

What is the fallopian canal, and what passes through it?

• Non-auditory bony channel covered with mucus membrane • Facial nerve (CN VII) passes through it to the ME

Which wall of the middle ear is the tegmental wall?

The roof (superior wall)

What space in the ME sits above the TM and holds the head of the malleus and top of the incus?

Epitympanic recess (tympanic aditus or antrum)

What does the epitympanic recess communicate with, and in which direction?

Upward and backward with the mastoid antrum

What is the papery-thin roof of the middle ear called?

Tegmen tympani

What is the posterior wall of the middle ear also called?

Mastoid wall

What is the horn on the posterior wall through which the stapedius muscle enters the ME?

Pyramidal eminence

How does the pyramidal eminence connect to the stapes?

To the posterior crus of the stapes via the stapedius tendon

What does the facial nerve (CN VII) innervate?

• Muscles of the face • Stapedius muscle

Which cranial nerve is the longest, and where does it start?

• Facial nerve (CN VII) • Starts in the pons

Which branch of the facial nerve passes through the ME and carries taste?

Chorda tympani nerve

The chorda tympani carries taste from which part of the tongue?

Anterior-lateral 2/3

Which nerve is often damaged during middle ear surgery?

Chorda tympani nerve

What is the floor (inferior wall) of the middle ear called, and what lies below it?

• Tympanic plate • Jugular bulb (fossa) lies below the ME

What major vessel lies anterior to the anterior wall of the middle ear?

Carotid artery

What two structures are associated with the anterior wall of the middle ear?

• Eustachian tube • Tensor tympani muscle

What nerve innervates the tensor tympani?

Trigeminal nerve (CN V)

Where does the tendon of the tensor tympani insert?

Manubrium of the malleus

What encases the tensor tympani, and which part of it enters the ME?

• Bony semi-canal • Only the tendon enters the ME

How long is the tensor tympani, and where does it lie relative to the Eustachian tube?

• 25 mm long • Runs parallel to and above the Eustachian tube

What are the common names for the malleus, incus, and stapes?

• Malleus: hammer • Incus: anvil • Stapes: stirrup

What are the parts of the malleus?

• Manubrium • Lateral process • Neck • Head

Which part of the malleus is embedded in the TM, and in which layer?

• Manubrium • Middle (fibrous) layer

What are the weight and length of the malleus?

• 23-27 mg • 7.5-9 mm long

What are the parts of the incus?

• Short process • Long process • Articular facet • Lenticular process

Which part of the incus connects to the malleus?

Articular facet

Which part of the incus sits squarely on the head of the stapes?

Lenticular process (at the incudostapedial joint)

What are the lengths of the long and short processes of the incus?

• Long process: 7 mm • Short process: 5 mm

What are the parts of the stapes?

• Head • Neck • Anterior crus • Posterior crus • Footplate

Which crus of the stapes is longer and thicker?

Posterior crus

Where does the stapes footplate fit?

Into the oval window

Which ring-shaped ligament holds the stapes footplate in the oval window?

Annular ligament

What are the weight, height, and maximum displacement of the stapes?

• 2.86 mg • 3.26 mm high • 0.1 mm maximum displacement

What is the smallest muscle in the body, and how long is it?

• Stapedius muscle • 6-7 mm long

Where does the stapedius tendon attach?

Neck of the stapes, posteriorly

What nerve innervates the stapedius?

Facial nerve (CN VII)

What is the function of the middle ear ligaments?

Suspend the ossicles in the ME cavity

What are the three ligaments of the malleus?

• Superior • Anterior • Lateral

What are the two ligaments of the incus?

• Superior • Posterior

What does a ligament connect vs. a tendon?

• Ligament: bone to bone • Tendon: bone to muscle

What are the joints of the ossicular chain?

• Incudomalleolar (incudomalleal) • Incudostapedial • Stapediovestibular

What are the two middle ear muscles?

• Tensor tympani • Stapedius

What are the three functions of the tensor tympani?

• Works with the TM in a diaphragm pump to eliminate positive ME pressure • Works with tensor veli palatini and levator palatini to help open the E. tube • Activated by loud sound and tactile stimulation (minor role in acoustic reflex)

Which middle ear muscle is critical for the acoustic reflex?

Stapedius

Why can't the acoustic reflex protect against impulse noise?

The stapedius reflex is too slow

How does the stapedius move the stapes footplate?

Moves the anterior portion of the footplate in and out

What does the Eustachian (auditory) tube connect?

Middle ear to the nasopharynx

Which end of the Eustachian tube is always open, and which is closed?

• Middle ear end: always open • Nasopharyngeal end: closed

When does the Eustachian tube open briefly?

• Swallowing • Yawning • Sneezing • Change in altitude

Describe the adult Eustachian tube.

• 35-38 mm long • Narrow • About 45 degrees • Runs medial-anterior

Describe the child Eustachian tube.

• Short • Wide • 0-10 degrees • Stays open

What are the three functions of the Eustachian tube?

• Ventilation: equalizes ME pressure with ambient • Protection: from outside fluids, bacteria, viruses • Drainage: of fluids secreted from the ME

What are the steps of the Valsalva maneuver?

• Pinch your nose closed • Close your mouth • Forcefully exhale • Bear down • Hold 10-15 seconds

What is a transducer, and which ME structures act as transducers?

• Changes energy from one form to another • Tympanic membrane • Stapes footplate

The middle ear overcomes a mismatch between what two media?

Air in the outer ear and fluid in the inner ear (impedance mismatch)

Is the middle ear an amplifier?

No; it overcomes the impedance mismatch

About how much hearing loss would occur without the middle ear?

About 30 dB

What is the area ratio ('thumb tack') mechanism?

• TM area: 65 mm2 • Stapes footplate area: 3.2 mm2 • About 13.5:1 ratio (TM to OW) • Increases pressure at the oval window

Which ME mechanism uses the position of the rigid ossicular chain to increase pressure at the oval window?

Lever action

Which ME mechanism relies on the conical TM buckling so the malleus moves less than the TM?

Catenary action

What ossicular chain reconstruction prosthesis was shown in class?

Kraus K-Helix prosthesis

Which laser procedures place a prosthetic stapes?

• Stapedectomy • Stapedotomy

Which portion of the temporal bone houses the hearing apparatus?

Petrous portion

Congenital middle ear malformations usually come from maldevelopment of which embryological structures?

First and second branchial arches

Why are congenital middle ear malformations considered 'red flags'?

They may or may not come with other abnormalities

What are the four specific problems that occur with congenital ME malformations?

• Problems with the ossicles • Failure of the TM to develop • Persistent or partial bony plate • Fixation of the ossicles

What is the most significant and common congenital ME abnormality?

Fixation of the ossicles

What may be found with fixation of the malleus OR incus alone?

• Normal hearing • Abnormal (stiff) impedance • Possible ossification of the ligaments

What may be found with fixation of BOTH the malleus and incus?

• Fixation in the epitympanum (possible maximum conductive loss) • Ossification of ligaments

With congenital stapes fixation, what two forms can the stapes take?

• Deformed • Just fixated

What is triple fixation?

Fixation involving all 3 ossicles

What are the causes of triple fixation?

• Congenital malformation (most common) • New bony growth • Soft tissue changes • Consequences of skull fractures or surgical trauma

What are the findings with absence of the stapedial tendon?

• Unilateral absence of the acoustic reflex threshold • Usually normal hearing

What type of loss does the audiologic evaluation show with congenital ME malformations?

Conductive loss

Which parts can be affected in congenital ME malformations?

• Tympanic membrane • Ossicles • Ligaments • Middle ear cavity • Mastoid air cells • Eustachian tube

Differential diagnosis of congenital ME malformations considers which areas?

• Tympanic membrane • Middle ear • Related structures