Structures in the Ear

Nerves

facial (C.N. VII)

geniculate ganglion – sensory ganglion of CN VII

greater petrosal – carries parasympathetic innervation from to the pterygopalatine ganglion

chorda tympani – branch of CN VII that runs through the middle ear on course to give sensory taste innervation of the anterior 2/3 of the tongue; runs with the lingual nerve

vestibulocochlear (C.N. VIII)

Muscles

stapedius – interior of pyramidal eminance of the tympanic cavity to neck of stapes

innervation: tympanic branch of facial

action: depresses the base of the stapes

tensor tympani – auditory tube, sphenoid bone, temporal bone

innervation: mandibular branches through otic ganglion

action: tightens tympanic membrane; prevents damage from loud sounds

Bones

ossicles – serve to decrease the amplitude and increase the force of vibrations transmitted to the cochlea

malleus (hammer) – handle is imbedded in tympanic membrane; head articulates with the incus

the tensor tympani muscle inserts in the handle, and the chorda tympani nerve crosses over the neck

incus (anvil) – body articulates with the malleus; long process of the incus articulates with the stapes

stapes (stirrup) – head articulates with incus, base inserts on the oval window of the tympanic cavity

temporal

mastoid process – attachment of the sternocleidomastiod muscle

internal acoustic meatus – transmits the facial nerve; vestibulocochlear nerve; labyrithine artery

external acoustic meatus – extends from the concha of the ear to the tympanic membrane; medial 2/3 is bony and lined by thin skin continuous with tympanic membrane, lateral 1/3 is cartilagenous and lined with skin of the ear; innervation from 3 CN’s Þ V₃ (auriculotemporal nerve); VII (branches of tympanic plexus); X (auricular branch)

mastoid air cells – air pockets in mastoid bones

carotid canal – carries the carotid artery; opens into the foramen lacerum

greater petrosal hiatus – in the posterior portion of the middle cranial fossa; contains greater petrosal nerve

stylomastoid foramen – facial nerve passes out of the skull here

Bony Regions

jugular fossa – depression in the petrosal portion of the temporal bone; lies inferior to the jugular foramen

middle ear cavity – cavity in the petrous part of the temporal bone

contains: three ossicles, air, stapedius and tensor tympani muscles, chorda tympani nerve

tegmen tympani – thin sheet of bone that forms the roof of the middle ear (tympanic cavity)

epitympanic recess – part of the middle ear that lies superior to the tympanic membrane; superior to chorda tympani nerve; contains the body of the incus and the head of the malleus

aditus ad antrum – superior border of the epitympanic recess; is the opening to the mastoid antrum

mastoid antrum – lies superior and posterior to the epitympanic recess

promontory of the cochlea – bulge in medial wall of the tympanic cavity formed by the first turn of the cochlea

fenestra vestibuli (oval window) – attachment of base of stapes transmits vibration to perilymph of the tympanic cavity

fenestra cochleae (round window) – inferior to the oval window; allows perilymph to move in response to movement at the oval window (because you can’t compress a fluid)

inner ear cavity – embedded in the petrous part of the temporal bone; contains the vestibulocochlear organ

semicircular canals – anterior, posterior, lateral; bony canals that are part of the vestibular system; the semicircular ducts and the membranous portion of the cochlea lie within

middle cranial fossa – anterior to the petrous part of the temporal

posterior cranial fossa – posterior to the petrous part of the temporal

Membrane

tympanic membrane – lies at medial end of external acoustic meatus; divides external and middle ear; is concave towards the meatus, and the handle of the malleus froms a central depression called the umbo

Miscellaneous

vestibule of the ear – bony chamber lies just on the other side of the round window; continuous with the semicircular canals; contains the utricle and saccule which are parts of the vestibular system

auditory (eustachian) tube – connects nasopharynx to the middle ear; ~4cm long; posterior 1/3 is bony, rest is cartilage; bony part lies in a groove between the petrous part of the temporal and the greater wing of the sphenoid