Ear / Temporal Bone Anatomy

 

External Ear

Structure
Description / Clinical Relevance
Auricle (Pinna)
Cartilaginous outer ear that captures sound; landmarks include helix, antihelix, tragus, lobule.
External auditory canal (meatus)
2.5 cm canal leading to tympanic membrane; outer 1/3 cartilaginous, inner 2/3 bony. Contains ceruminous glands (earwax).
Tympanic membrane (eardrum)
Thin membrane separating external and middle ear; transmits sound vibrations to ossicles. Key surgical landmark for tympanotomy or tube placement.

Middle Ear

Function: Converts sound waves into mechanical vibrations and amplifies them.
Structure
Description / Clinical Relevance
Ossicles
3 tiny bones transmitting sound to inner ear: • Malleus (attached to tympanic membrane) • Incus (articulates with malleus & stapes) • Stapes (footplate sits in oval window of cochlea)
Eustachian (pharyngotympanic) tube
Connects middle ear to nasopharynx for pressure equalization; common site for infection in children.
Tensor tympani muscle
Dampens loud sounds by tensing the tympanic membrane (CN V₃ innervation).
Stapedius muscle
Stabilizes stapes to prevent excessive vibration (CN VII innervation).
Facial nerve (CN VII)
Passes through middle ear via facial canal; vulnerable in temporal bone fractures or surgery.
Chorda tympani (branch of CN VII)
Crosses middle ear; carries taste from anterior 2/3 tongue — injury causes loss of taste or altered salivation.

Inner Ear

Function: Converts mechanical vibrations into neural signals (hearing) and detects head motion (balance).
Component
Substructures & Function
Cochlea
Spiral-shaped organ for hearing; contains Organ of Corti (hair cells convert mechanical to electrical signals → CN VIII cochlear division).
Vestibule
Central cavity between cochlea and semicircular canals; contains utricle & saccule for linear acceleration (gravity).
Semicircular canals (3)
Detect angular acceleration (rotation) in 3 planes; communicate with vestibule.
Cochlear and vestibular nerves
Merge to form CN VIII (vestibulocochlear nerve); transmits sound and balance info to brainstem (pontomedullary junction).

Cochlea

notion image
 

Vestibule

  • lateral and posterior to cochlea
 

Malleus

  • lateral and anterior to cochlea
 

Superior semicircular canal

  • oriented in vertical plane perpindicular to long-axis of petrous temporal bone