OTOLOGY 1: ANATOMY & PHYSIOLOGY OF THE EAR, EAR DISCHARGE

What are the 3 anatomical divisions of the ear?

External, middle, and inner ear

What are the 5 parts of the temporal bone?

Squamous, mastoid, tympanic, zygomatic, and petrous

What sensory organs are contained within the temporal bone?

The organs of hearing and balance

What major vascular structures are contained within or closely related to the temporal bone?

Carotid artery and jugular venous drainage system

What intracranial structures are intimately related to the temporal bone?

Dura of the middle and posterior cranial fossae

What does the temporal bone articulate with anteriorly?

The condyle of the mandible

How does the mastoid air cell system communicate with the middle ear?

Via the aditus ad antrum

What major nerve passes through the temporal bone?

The facial nerve (CN VII)

What is the external ear defined as?

The portion of the ear external to the tympanic membrane

What are the main functions of the external ear?

Protects the tympanic membrane and collects/directs sound

What is another name for the sound-collecting function of the external ear?

Acoustic antenna

What role does the external ear play besides collecting sound?

Sound localization

What structures of the external ear act together as a resonator?

The auricle and concha

What is the resonant peak of the auricle/concha?

Approximately 2.5 kHz

What is the effect of the auricle/concha resonance on sound?

It increases sound pressure level

In what direction does external ear canal skin migrate?

Laterally

What is the rate of external ear canal skin migration?

Approximately 2 mm/day

Where does external ear canal skin migration begin?

At the umbo of the malleus

Where does external ear canal skin migrate toward?

The external auditory meatus

Why is lateral migration of external ear canal skin important?

It helps maintain patency and self-clean the canal

What is the auricle primarily composed of?

Elastic cartilage

What covers the cartilage of the auricle?

Closely adherent skin

Pinna = what other term?

Auricle

How many auricular hillocks form the pinna?

Six hillocks of His

What embryologic structures form the auricular hillocks?

1st and 2nd pharyngeal arches

What can failure of auricular hillock fusion cause?

Preauricular sinus

What is a major acoustic function of the pinna?

Diffracts and focuses sound waves

What is the adult EAC divided into anatomically?

1/3 cartilaginous and 2/3 bony

What characterizes the cartilaginous EAC?

Thick skin with ceruminous and sebaceous glands

What characterizes the bony EAC?

Thin skin directly over bone; no skin appendages

Where is cerumen produced?

In the cartilaginous EAC

What is the direction of the EAC's curvature in adults?

Anteriorly and medially

What part of the tympanic membrane may the EAC curvature obscure?

Anterior tympanic membrane

How does the bony EAC differ in children?

It comprises less than two-thirds of the canal

What is the middle ear?

An air-filled space communicating with the nasopharynx

What connects the middle ear to the nasopharynx?

Eustachian tube

What structure seals the middle ear laterally?

Tympanic membrane

What is the main acoustic function of the middle ear?

Transmits and amplifies sound to the stapes

Why does the middle ear amplify sound?

To improve energy transfer from air to inner-ear fluid

To which inner-ear window does the stapes transmit sound?

Oval window

What window is protected from direct sound by the middle ear?

Round window

What is the approximate diameter of the tympanic membrane?

1 cm

What is the shape of the tympanic membrane?

Slightly ovoid and conical

What maintains the conical shape of the tympanic membrane?

Malleus attachment

What are the 3 layers of the tympanic membrane?

Epidermal, fibrous, and mucosal

What is the outer layer of the tympanic membrane?

Squamous epithelium

What is the middle layer of the tympanic membrane?

Fibrous layer

What is the inner layer of the tympanic membrane?

Respiratory mucosa

What is the outer TM layer continuous with?

Skin of the external auditory canal

What is the inner TM layer continuous with?

Mucosa of the middle ear

What is the pars tensa?

The major portion of the tympanic membrane

How many layers does the pars tensa contain?

Three layers

What is the pars flaccida?

The superior, smaller portion of the tympanic membrane

Where is the pars flaccida located?

Superior to the lateral process of the malleus

Which TM layer is deficient in the pars flaccida?

Fibrous middle layer

What is the annulus of the tympanic membrane?

A peripheral thickening of its fibrous layer

Where is the annulus deficient?

Superiorly at the pars flaccida

Where does the chorda tympani run in relation to the TM?

Between the fibrous and mucosal layers

Which cranial nerve gives rise to the chorda tympani?

Facial nerve (CN VII)

What is the primary function of the tympanic membrane?

Transmit sound vibrations to the middle ear

What is the approximate total area of the tympanic membrane?

75-80 mm²

What is the approximate effective vibrating area of the TM?

55 mm²

Can tympanic membrane perforations heal spontaneously?

Yes, especially small acute perforations

What determines whether a TM perforation heals?

Size, location, cause, and patient factors

Where does stapes movement transmit pressure first?

Scala vestibuli via the oval window

How does the pressure wave travel through the cochlea?

Scala vestibuli → helicotrema → scala tympani

Where does the pressure wave ultimately dissipate?

Round window

What is the role of scala media in sound transmission?

Contains the organ of Corti; it is not the main pressure-wave pathway

What is the external ear acoustically?

The final part of the external auditory sound-collecting system

What type of tube is the external auditory canal acoustically?

A tube open at one end

What are the 4 quadrants of the tympanic membrane?

Posterosuperior, posteroinferior, anterosuperior, anteroinferior

What nerve innervates the tensor tympani?

Mandibular division of CN V (V3)

What does contraction of the tensor tympani do?

Pulls malleus medially and decreases TM vibration

What is the protective function of tensor tympani contraction?

Reduces transmission of excessive sound energy

What nerve innervates the stapedius?

Facial nerve (CN VII)

What does contraction of stapedius do?

Pulls the stapes posteriorly and reduces its movement

How can the stapedius reflex be assessed clinically?

By detecting changes in middle-ear impedance/admittance

What is the roof of the middle ear called?

Tegmental wall

What is the floor of the middle ear called?

Jugular wall

What is the posterior wall of the middle ear called?

Mastoid wall

What is the anterior wall of the middle ear called?

Carotid wall

What is the lateral wall of the middle ear called?

Membranous wall

What is the medial wall of the middle ear called?

Labyrinthine wall

What are the 3 auditory ossicles from lateral to medial?

Malleus, incus, stapes

What are the common names of the ossicles?

Malleus = hammer; incus = anvil; stapes = stirrup

Which ossicle is attached to the tympanic membrane?

Malleus

Which parts of the malleus are visible through the TM?

Handle and lateral process

Which part of the incus may be visible through the TM?

Long process

Where is the long process of the incus seen through the TM?

Posterior-superior quadrant

Where does the stapes footplate sit?

Oval window

What does the stapes footplate contact?

Inner-ear fluid via the oval window

What is the main function of the ossicles?

Impedance matching and protection

How do ossicles facilitate impedance matching?

Increase efficient transfer of sound energy to inner-ear fluids

How do ossicles contribute to protection?

Reduce transmission of excessive sound energy

Are the auditory ossicles adult-sized at birth?

Yes

What are the 4 major spaces of the middle ear?

Epitympanum, mesotympanum, protympanum, hypotympanum

What is another name for the epitympanum?

Attic

What does the epitympanum contain?

Head of malleus and body of incus

How does the epitympanum communicate with the mastoid?

Through the aditus ad antrum

What is the mesotympanum?

The middle-ear space at the level of the tympanic membrane