L7. The ear

Question 1

What are the two parts that make the external ear

Answer 1

Auricle and External acoustic meatus

Question 2

Describe the structure and innervation of the auricle

Answer 2

Cartilage covered with skin used for capturing sound.

Innervated

a) superficially: cervical plexus and CNV3
b) deeper (more central) parts by: CN10 + 7

Question 3

Describe the structure and innervation of the External acoustic meatus

Answer 3

Extends from the concha to the tympanic membrane for 2.5 cm.
It doesn’t follow a straight course, going up then back and front down. The lateral 1/3 is cartilaginous and the medial 2/3 is bony tunnel.

Innervated by CN V3, 10 and 7

Question 4

What is the innervation of the tympanic membrane

Answer 4

Outer surface: CNV3, 10, 7 and 9 (small contribution)

Inner surface: CN9 (tympanic branch)

Question 5

How should you examine the ear using otoscope for adults/babies

Answer 5

Adult: pull the auricle superiorly, look through otoscope to determine it is straight before you place head in.
Put it in gradually so can see the mucous membrane as go along

Baby pull ear down

Question 6

What are the names of the boundaries of the middle ear and describe this space

Answer 6

Middle ear is an air filled space with a tympanic cavity and epitympanic recess (sup), within the temporal bone and lined with mucous membrane.

Walls 
Roof: Tegmental
Floor: Jugular
Lateral: Membranous 
Medial: Labyrinthine
Posterior: Mastoid 
Anterior: Carotid

Question 7

Describe which space does the Roof separate the middle ear from and if there are any structures entering/exiting this wall.

Answer 7

• the Tegmen Tympani (thin plate of petrous bone) separates dura mater on the floor of the middle cranial fossa from the tympanic cavity
• Prominence of Lateral semicircular canal does down through the roof, passing to the posterior wall

Question 8

Describe which space does the Floor separate the middle ear from and if there are any structures entering/exiting this wall.

Answer 8

• separates from internal jugular vein.

- On medial border the tympanic branch of the CN9 nerve enters the ear to join the tympanic plexus

Question 9

Describe which space does the Lateral wall separate the middle ear from and if there are any structures entering/exiting this wall and what is it made of

Answer 9

-separates the middle ear from external ear

Made of tympanic membrane except for the upper part (bony lateral wall of epitympanic recess)

Question 10

Describe which space does the Medial wall separate the middle ear from and if there are any 7 structures entering/exiting this wall.

Answer 10

• separates middle from inner ear.
• Associated with promontory produced by the basal coil of the cochlear. covered with mucous membrane containing the
• Tympanic plexus
• Oval window (1st-sup)
• Round window (2nd-inf)
• Prominence of the facial canal
• Prominence of the lateral semicircular canal
• Lesser petrosal nerve exiting the tympanic plexus to go to the anterior wall

Question 11

What nerves make up the tympanic plexus and what is the course of the lesser petrosal nerve

Answer 11

9th cranial and caroticotympanic nerves(sympathetic fibres from internal carotid plexus).
Lesser petrosal nerve is a branch of the tympanic plexus.
Exits the middle ear to run along the middle cranial fossa. Exits that to reach the otic ganglion carrying pre-ganglionic parasympathetic fibres

Question 12

Where can infections from the middle ear travel through and what are the 5 possible complications of middle ear infection

Answer 12

• Persistent Otitis media can enter Mastoid cells causing Mastoiditis: Mastoid process isn’t prominent in babies but with infection is red and warm.
• Middle ear infections can travel upwards through the tegmen which sits on bone that is very thin - meningitis or brain abscess
• Through eustachian tube: to nasopharynx - otitis media in children
• Facial nerve canal: swelling from the infection can compress the canal causing facial nerve palsy
• Internal ear: Labyrinthitis

Question 13

Describe which space does the Posterior wall separate the middle ear from and if there are any structures entering/exiting this wall.

Answer 13

• separates middle ear from Mastoid air cells inferiorly and continues to the mastoid antrum via aditus superiorly.
• The tendon of the stapedius muscle and
• branch of the 7th cranial nerve (chorda tympani) enters the middle ear here

Question 14

Describe which space does the Anterior wall separate the middle ear from and if there are any 4 structures entering/exiting this wall.

Answer 14

• separates it from the internal carotid artery inferiorly
• Superiorly: the pharyngotympanic tube + tensor tympani muscle enter
• Nerve branches from the internal carotid plexus (carticotympanic nerves) enter here
• Chorda tympani nerve exits through the inferior part of this wall

Question 15

What happens if you damage the chorda tympani nerve and what is its course

Answer 15

-Enters middle ear through Posterior wall
-Runs behind tympanic membrane: at variable heights
- Exits through Anterior wall
-Runs with lingual nerve to go to the tongue
If damaged then loss of taste from ant 2/3 of tongue (branch of CN7) and loss of presynaptic preganglion fibres to submandibular and sublingual salivary glands: dry mouth

Question 16

What is the innervation, arterial and venous supply to the middle ear

Answer 16

• N: Tympanic plexus:

Arterial

• tympanic branch of the maxillary artery
• mastoid branch of the occipital/posterior auricular arteries

Venous
-via pterygoid plexus of veins and the superior petrosal sinus

Question 17

What are the 4 major contents of the middle ear

Answer 17

1. Auditory ossicles: malleus, incus, stapes
2. Muscles: tensor tympani + stapedius
3. Chorda tympani nerve: branch of CN7
4. Tympanic nerve plexus: tympanic branch of CN9 + caroticotympanic nerves of internal carotid plexus

Question 18

What is the clinical importance of innervation of the external ear.

Answer 18

Need to examine the external ear if feeling headaches.

Damage to the external surface of tympanic membrane could radiate to other parts as innervated by vagus and facial nerve
(Internal surface by 9)