L5: Ear

Question 1

External acoustic meatus

Answer 1

Has outer cartilaginous portion and inner bony portion

Innervated by [V3], [X], [VII]

2-3cm long and does not follow straight course and so you have to pull ear superiorly, posteriorly and laterally to straighten and see with otoscope

Question 2

Clinical: Swimmers ear

Answer 2

Otitis externa

Infection in mucosa inside external meatus

Question 3

Clinical: Surfers ear

Answer 3

Cold water causing bony part to grow, constricting meatus = reduces hearing

Question 4

Innervation of auricle

Answer 4

Superficial = cervical plexus, [V3]
Deeper = [VII] and [X]

Question 5

Middle ear consists of…

Answer 5

Tympanic cavity and epitympanic recess

Question 6

Roof of middle ear

Answer 6

= Tegmental wall

Separates middle ear from middle cranial fossa

Question 7

Floor of middle ear

Answer 7

= Jugular wall

• Separates middle ear from internal jugular v (just below)
• Tympanic branch [XI] (forms tympanic plexus, parasympathetic)

Question 8

Lateral wall of middle ear

KNOW

Answer 8

= Membranous wall (tympanic membrane + epitympanic recess)

Separates middle ear from ext auditory meatus

Tympanic membrane innervation:

• Outer surface = [V3], (X, VII, IX)
• Inner surface = IX

Question 9

Medial wall

Answer 9

= Labyrinthine wall
Separates middle ear from inner ear (vestibulocochlear apparatus)
- Promontory covered by mucous membrane containing tympanic plexus (IX and caroticotympanic nerve)
- Oval and round windows
- Tympanic plexus
- Lesser petrosal n (parasympathetic from
tympanic plexus)

Question 10

Anterior wall

Answer 10

= Carotid wall
Separates middle ear from int carotid a inferiorly
- Pharyngotympanic tube (eustachian tube,
has bony part and cartilaginous part - otitis
media in children)
- Tensor tympani muscle
- Chorda tympani nerve (runs right behind tympanic membrane so can be damaged leading to loss of taste from ant 2/3 of tongue)
- Carotidotympanic nerves

Question 11

Posterior wall

Answer 11

= Mastoid wall

• Stapedius tendon
• Chorda tympani nerve
• Aditus to mastoid antrum (and mastoid air cells)

Question 12

Clinical: spread of infection from ear into skull

Answer 12

Mucous membrane lining mastoid air cells is continuous with mucous membrane throughout middle ear - infection in middle ear can easily spread into mastoid area
Infection in mastoid antrum/air cells usually secondary to infection in middle ear = mastoiditis
Osteomyelitis can develop spreading into middle cranial fossa –> meninigits
Drainage of pus in mastoid air cells - take care not to damage mastoid wall (damage facial n)

Question 13

Contents of middle ear

Answer 13

Muscles, ossicles (malleus, incus, stapes), chorda tympani n (branch of facial n), tympanic nerve plexus

Question 14

Tympanic nerve plexus

Answer 14

Contributions from tympanic n (from glossopharyngeal n) - sympathetic
and carotidotympanic n (branch from int carotid plexus) - parasympathetic

Lesser petrosal n goes out from plexus carrying parasympathetic fibres

Question 15

Tympanic membrane parts

Answer 15

Umbo (end of handle of malleus)
Handle of malleus
Posterior malleolar fold
Pars flaccida
Lateral process (of malleus)
Anterior malleolar fold
Cone of light (if can't see could be infection behind tympanic membrane)

Question 16

Middle ear blood supply

Answer 16

Arterial:
Tympanic branch of maxillary a
Mastoid branch of occipital or post auricular arteries

Venous drainage:
Via pterygoid plexus of veins and superior petrosal sinus