c. Fenestra cochlea or round window
Anterior wall
Separates tympanic cavity from carotid canal
Superiorly has opening of auditory tube and canal for tensor tympani
Posterior wall
Superiorly, aditus (opening) to mastoid antrum, connecting to mastoid air cells
Between posterior wall and aditus, prominence of canal of facial nerve
Pyramidal eminence
a. Tiny cone-shaped prominence
b. Contains proximal attachment of stapedius muscle
Lateral wall
Tympanic membrane
Lateral wall of epitympanic recess
Handle of malleus
Ossicles
Chain of bones across tympanic cavity
Extend from tympanic membrane to oval window on medial wall
Handle of malleus attaches to tympanic membrane and head articulates with incus
Incus articulates with head of malleus and end of long limb with stapes
Head of stapes articulates with long limb of incus and base (foot-plate) fits into oval window on medial wall
Increase the force but decrease amplitude of vibrations from tympanic membrane
Auditory (pharyngotympanic) tube
Formerly called Eustachian tube
= Communication between middle ear and nasopharynx
Allow equalisation of atmospheric pressure in middle ear
Actively opened by coordinated contractions of levator and tensor veli palatine muscles
Muscles
Function to dampen movement of auditory ossicle
Tensor tympani
Stapedius
Nerves
Chorda tympani
Branch of facial nerve (cranial nerve [CN]) VII
Emerges from facial canal through canaliculus in posterior wall of middle cavity
Carries taste fibers to anterior two thirds of tongue
Crosses medial surface of neck of malleus
Exits anteriorly via canaliculus to petrotympanic fissure
Tympanic plexus
On the promontory of the medial wall
Contributions from tympanic branch of glossopharyngeal (CN IX)
Twigs from internal carotid plexus
Twig from facial nerve
Supplies
a. Mucous membrane of tympanic cavity
b. Mastoid antrum
c. Mastoid air cells
d. Auditory tubeInner Ear
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Concerned with the reception of sound and maintenance of balance
Buried within petrous portion of temporal bone
Membranous labyrinth suspended within bony labyrinth
Bony labyrinth
Occupies lateral region of petrous ridge of temporal bone
= Space filled with perilymph
Surrounded by bony capsule harder than petrous bone
Cochlea
Concerned with hearing
Contains the membranous cochlear duct
Consists of
a. Spiral canal
b. Bony core, the modiolus
Canal spirals around modiolus
Basal turn forms promontory of medial wall of tympanic cavity
At basal turn, bony labyrinth communicates with subarachnoid space above jugular foramen via cochlear aqueduct
Vestibule
Small oval chamber
Contains membranous utricle and saccule
Oval window is on lateral wall
Continuous with
a. Cochlea anteriorly
b. Semicircular canals posteriorly
Communicates with posterior cranial fossa via aqueduct of vestibule
a. Extends to posterior surface of petrous ridge of temporal bone