Anatomy of outer and middle ear

Question 1

Why are there 3 different parts to the ear?

Answer 1

Because they come from 3 different embryonic origins

Question 2

What does the outer ear do?

Answer 2

Funnels sound towards tympanic membrane and middle ear.

Question 3

What does the middle ear do?

Answer 3

Transducers sound energy into movements of joins of the ossicle chain. Synovial joints and displacements of bones are translated as pressure on the oval window, triggering movement of perilymph in the cochlear, displacing hair cells.

Question 4

What does the inner ear do?

Answer 4

Transducers movements of the ossicle chain into electrical impulses of hearing

Question 5

What is the embryological origin of the outer ear?

Answer 5

1st pharyngeal cleft - ectodermal origin

Question 6

What is the sensory supply to the outer ear?

Answer 6

Sensory supply shared between first and second arch nerves - trigeminal and facial nerves

Question 7

What arch does the middle ear derive from?

Answer 7

1st pharyngeal pouch - endodermal origin

Question 8

What is the motor supply to the middle ear?

Answer 8

Motor supply to tensor tympani - 1st arch - motor division of trigeminal, CNV3
Motor supply to stapedius - 2nd arch - motor division of CNVII (facial)

Question 9

What is the embryological derivation of the inner ear/pharynx?

Answer 9

Inner ear not covered so replaced by pharynx due to similar embryology.
Pharynx (mucosa lining pharynx and auditory tube). 1st and 2nd pharyngeal pouch, endoderm all origin. Crypts of palatine tonsil.

Question 10

What is the outer ear divided into?

Answer 10

Pinna and external auditory canal

Question 11

What is the pinna made from?

Answer 11

Skeleton is made from elastic cartilage, covered by skin.

Question 12

What is cauliflower ear?

Answer 12

Cauliflower ear results from necrosis of pinna cartilage if subcutaneous bleeds are not drained in good time.

Question 13

What is the detailed sensory innervation of the skin of the outer ear supplied by?

Answer 13

Less occipital nerve (C2) (posterior)
Trigeminal nerve - auriculotemporal nerve (superior part)
Facial nerve - auricular branch (EAM)
Vagus nerve - auricular branch
Greater auricular nerve

Question 14

What is the vagus nerve part of?

Answer 14

Part of the ear-cough reflex

Question 15

What is the outer 1/3 of th external auditory canal made of and lined by?

Answer 15

Elastic cartilage.
Skin is hairy (with cilia), has ceruminous glands that secrete bactericidal wax, to trap dust, has sebaceous gland.

Question 16

What is inner 1/3 of EAC made of?

Answer 16

Comprises of the tympanic plate of the temporal bone
All lined with skin even the outer plate of tympanic membrane
No hair

Question 17

What are the 3 layers of the tympanic membrane made up/lined with?

Answer 17

Lateral - keratinised stratified squamous cells
Middle - fibrous layer
Medial - respiratory epithelium (columnar)

Question 18

What supplies sensation to the inner surface of the tympanic membrane?

Answer 18

Glossopharyngeal nerve CNIX

Question 19

What supplies sensation to the external surface of the tympanic membrane?

Answer 19

Auriculotemporal nerve, branch of CNV3
Small branch of the vagus nerve

Question 20

What does middle ear function rely on?

Answer 20

Depends on continuous adequate ventilation of this chamber

Question 21

What happens if there poor oxygenation of the middle ear?

Answer 21

Leads to changes in metabolism of the epithelium lining the chamber, ultimately resulting in middle ear dysfunction, mastoiditis, meningism, septicaemia and death.

Question 22

What is the function of the ossicles?

Answer 22

3 bones that connect the TM to the inner ear. They act as an impedance matching device for the sound travelling from air to the endolymph. They trigger perilymph movement in the cochlear.

Question 23

What muscles attaches to the stapes and what does it do?

Answer 23

Stapedius - dampens the movements of the stapes (supplied by CNVII)

Question 24

What muscle attached to the malleus and what does it do?

Answer 24

Tensor tympani dampens the vibrations of the malleus by tensing the tympanic membrane. (Supplied by CNV3)

Question 25

What does the stapes connect to?

Answer 25

Oval window

Question 26

What are the 6 walls of the middle ear cavity?

Answer 26

Lateral wall is inner plate of tympanic membrane
Medial wall is outer plate of oval window
Roof is tegmen tympanum
Floor is jugular wall
Posterior wall is mastoid wall
Anterior wall is carotid wall

Question 27

What are the 2 compartments created if a line is drawn from the top of the tympanic membrane to the medial wall of the cavity?

Answer 27

Above line is epitympanic recess. Beneath line is tympanic cavity, continuous with the pharyngotympanic/auditory/Eustachian tube

Question 28

What does the air filled middle ear cavity communicate with?

Answer 28

Nasopharynx via the auditory tube
Mastoid air cells via the epitympanic recess and mastoid atrum (opening is the aditus of mastoid antrum)

Question 29

What is the function of the auditory tube?

Answer 29

Functions to equalise pressure across the membrane

Question 30

What does the angle of the Eustachian tube allow for?

Answer 30

Angle allows for secretions to be drained into the pharynx

Question 31

Which parts of the pharyngotympanic tube are bony and cartilage?

Answer 31

Posterior 1/3 is bony, rest is cartilaginous

Question 32

What muscles control the walls of the cartilaginous part of the Eustachian tube?

Answer 32

Opened by the action of the levator palatini and tensor veli palatini

Question 33

What is Eustachian tube dysfunction?

Answer 33

ETD leads to failure to drain mucous secretions of the middle ear, leading to congestion. This is otitis media.