Ear

Auricle (pinna) - lateral 1/3 of the external ear canal

Cartilage covered with skin

Medial 2/3 of the external ear canal

Temporal bone; passes through the external acoustic meatus of the skull

Glands in the lateral external ear canal

Sebaceous and ceruminous glands

Function of ceruminous glands

Produce cerumen (ear wax)

What separates the external ear canal from the middle ear?

The tympanic membrane

Shape and function of the tympanic membrane

Cone-shaped membrane that vibrates in response to sound waves

Which ossicle leaves an impression on the tympanic membrane?

The malleus

Sensory innervation of the EXTERNAL surface of the tympanic membrane

(CN V3) and (CN X)

Sensory innervation of the INTERNAL (middle ear side) surface of the tympanic membrane

Glossopharyngeal nerve (CN IX)

Three layers of the tympanic membrane and their embryologic origins

Outer epidermal layer (ectoderm), middle mesenchymal layer with collagen and elastic fibers, inner layer (endoderm)

Lateral border of the middle ear

Tympanic membrane

Medial border of the middle ear

Promontory, oval window, and round window

Posterior border of the middle ear

Mastoid antrum/air cells and stapedius

Three spaces contained in the middle ear

Epitympanic cavity, tympanic cavity, auditory (Eustachian) tube

Path of the chorda tympani?

through the middle ear

Stapes what does it do and its innervation?

dampen vibration, facial nerve (CN VII)

Tensor tympani innervation and function?

(V3) connects to the malleus, also dampens sound (chewing).

Function of the round window

Pressure release into the scala tympani (tympanic duct)

Function of the Eustachian (auditory) tube

Connects the middle ear to the nasal cavity and equalizes pressure behind the tympanic membrane

Why are children at higher risk for otitis media?

Their Eustachian tube is shorter and more horizontal

Path of the facial nerve (CN VII) through the temporal bone

Internal acoustic meatus, then facial canal, then exits at the stylomastoid foramen

Three branches of CN VII in the ear region

Greater petrosal nerve, nerve to stapedius, chorda tympani

Greater petrosal nerve - function

Parasympathetic to nasal mucosa glands, lacrimal glands, and palatine glands

Nerve of the pterygoid canal

Formed when the greater petrosal nerve joins the deep petrosal nerve

Nerve to stapedius - function

Motor to the stapedius muscle

Chorda tympani - functions

Taste to the anterior 2/3 of the tongue and parasympathetic to the submandibular and sublingual glands

Where does the glossopharyngeal nerve (CN IX) exit the skull? and main branches?

Jugular foramen (with the vagus nerve)

tympanic and lesser petrosal

Tympanic nerve (CN IX) - what plexus does it form and where?

The tympanic plexus, on the promontory (medial wall of the middle ear)

Tympanic nerve (CN IX) - sensory territory

Somatic sensory to the internal tympanic membrane and the mucosa of the middle ear

Lesser petrosal nerve - pathway and target

Travels through the foramen ovale, synapses at the otic ganglion, then supplies the parotid gland

Auditory apparatus - function, location, and main structure

Hearing; anteromedial; contains the cochlea

Vestibular apparatus - function, location, and main structures

Balance; posterolateral; fluid-filled semicircular canals and the vestibule

Vestibule

Central cavity of the inner ear containing the oval window

Oval window

Membrane-covered opening from the middle ear to the inner ear

Nerve of the inner ear and the opening it travels through

Vestibulocochlear nerve (CN VIII), through the internal acoustic meatus

Two divisions of CN VIII

Cochlear nerve (hearing) and vestibular nerve (balance)

Which other cranial nerve travels through the internal acoustic meatus with CN VIII?

Facial nerve (CN VII)

Tensor tympani - innervation and function

CN V3; attaches to the malleus and dampens loud sounds (chewing, shouting, thunder)

Stapedius - innervation and function

CN VII; smallest skeletal muscle; stabilizes the stapes to dampen vibration and protect the inner ear

Sequence of sound transmission

vibration is detected then the stapes moves the oval window, and perilymph moves

Base of the cochlea (near the oval window)

detects high frequencies

Apex of the cochlea (near the helicotrema)

low frequencies

Otitis media

Middle ear infection causing inflammation behind the tympanic membrane

Mastoiditis

Symptoms

Otitis media that spreads to the mastoid air cells posterior to the middle ear

Swelling, redness, and tenderness behind the ear with loss of the postauricular crease

Hearing test

Normal Rinne test

Weber test

Stapedius palsy (CN VII palsy) causes what hearing symptom?

Hyperacusis (sounds seem abnormally loud)

Paralysis of which muscle, supplied by which cranial nerve, causes hyperacusis?

Stapedius muscle, supplied by CN VII (facial nerve)

Why are children at increased risk of acute otitis media?

Their Eustachian tube is shorter and more horizontal