26. Ear Structure + Function

Question 1

Eustachian Tubes: where do they connect, where do they run

Temporal & Ear Ossicle Ossification:
Which parts of temporal/bone arise from - somites, 1st arch mesenchyme, 1st arch cartilage, 2nd arch cartilage

Answer 1

Eustachian tubes: from nasopharynx through middle ear (to mastoid air cells), run parallel to anterior border of petrous part of temporal bone

somites: petrous, mastoid
1st arch mesenchyme: squamous, tympanic
1st arch cartilage: incus, malleus
2nd arch cartilage: stapes, styloid

Question 2

Ear Development

What arises from 1st pharyngeal groove, 1st pharyngeal pouch, otic placode, arch 1 cartilage, arch 2 cartilage

Answer 2

1st pharyngeal groove - external auditory meatus
1st pharyngeal pouch - middle ear (mastoid antrum, air cells, tympanic cavity, auditory tube, tegmen tympani)
Otic Placode = otocyst - cochlea + semicircular canals
Arch 1 Cart - incus, malleus
Arch 2 Cart - stapes

Question 3

Middle Ear Borders (Roof, Floor, Ant, Post)

Answer 3

Roof: Tegmen tympani
Floor: Jugular Bulb
Ant: Internal Carotid a.; Auditory Tube
Post: CN VII

Question 4

What are the 3 ear ossicles? What is their function?

What are 2 ways the 3 ear ossicles address impedance mismatching?

Answer 4

malleus, incus, stapes
fx: transmit sound vibrations from TM to middle ear

1. concentrate TM forces to oval window (TM is 20x larger SA than oval window)
2. malleus/incus act as lever to amplify sound wave forces

Question 5

Tympanic Membrane:
What disease is indicated by the following:
Color (normal, amber, red, white/yellow, discrete white patches, yellow mass on TM)
Position (retracted vs bulging)

What are two signs of middle ear effusion?

Answer 5

Normal - pearly grey, clear, colorless
Amber - serous effusion, not infected/AOM
Red - many causes, not good predictor of AOM, could be increased vascularity
White/Yellow - purulent, AOM
Discrete White Patches - Tympanosclerosis
Yellow Mass - Cholesteatoma

Retracted - eustacian tube blocked/dysfx
Bulging - AOM

1. Fluid/Air Level
2. Bubbles

Question 6

Why are kids more likely to get AOM than adults?

What muscles are in the middle ear? What nerves are in the middle ear? What bone lies over the middle ear?

Answer 6

Stapedius m. (contracts to protect ear from loud noises, CN7)
Tensor Tympani m. (helps open eustachian tube, V3)

Nerves: Chorda tympani (taste, CN7), CN7, Greater petrosal N. (CN 7), pretrematic CN IX Tympanic N.

Bone: promontory

Question 7

What is the fluid within the membranous labyrinth and body labyrinth?
What are the locations and functions of the saccule, utricle, ampullae, and cochlea?

Answer 7

Endolymph - membranous; via endolymphatic duct
Perilymph - bony; from CSF via perilymphatic duct

Saccule + Utricle (bigger) - register linear acceleration + gravity
Ampullae: at start of each semicircular canal, where nerve impulse is generated for head positioning
Cochlea: electrical impulse for sound; 2.5 turns

Question 8

How does sound travel through the cochlea, and how does this generate an electrical signal?

Answer 8

Sound vibrations from oval window = perilymph = move cochlea membrane = shear force on membrane bends cilia hair cells = open voltage channel = depolarize cell = release of NT = nerve impulse

sound vibrations pass from oval window, up and back down cochlea, out round window

Question 9

Ear innervation: external auditory meatus vs. middle ear vs. inner ear

What are the three parasympathetic paths that traverse the middle ear?

Answer 9

Ext Auditory Meatus: general sensory from CNX (cutaneous branch, why you can cough from ear probing)
Middle ear: visceral sensory from tympanic branch of CN IX (can still produce sharp pains)
Inner ear: special sensory from CN 8 (hearing, balance)

1. Tympanic Nerve (CN9) - Lesser petrosal n - V3 auriculotemporal n. - parotid gland
2. Chorda Tympani (CN7) - V2 lingual nerve - tongue (taste)
3. Greater Petrosal N. (CN7) - V2 - lacrimal, nasal, palatal mucosa