The Ear

Question 1

External ear - diagram (right)

Answer 1

Question 2

Describe the external ear

Answer 2

• Auricle: elastic cartilage covered with skin
• External auditory meatus ~3cm long tube
  
  • Concha of auricle → tympanic membrane
    
    • Runs slightly anteriorly
  • Lat 1/3 cartilage, fibrous tissue posterosuperiorly
  • Medial 2/3 bony: grooved for attachment of tympanic membrane
  • Covered in hairy skin, ceruminous glands secrete wax

Question 3

Describe the middle ear

Answer 3

Hollowed out cave in the petrous part of the temporal bone, containing many structures

Transmits vibrations from tympanic membrane to inner ear

Question 4

Middle ear diagram (right)

Answer 4

Question 5

Roof of the middle ear

Answer 5

Plate of bone separating it from: middle cranial fossa, meninges & temporal lobe

Question 6

Floor of the middle ear

Answer 6

Thin plate of bone separating it from the jugular fossa and carotid canal

Question 7

Medial wall of the middle ear

Answer 7

Oval window to the inner ear, promontory due to first turn of cochlear

Question 8

Lateral wall of the middle ear

Answer 8

Tympanic membrane: bulges into middle ear i.e. lateral wall is concave

Question 9

Tympanic membrane - diagram, external view

Answer 9

Question 10

Describe the ossicles

Answer 10

3, transmit vibrations of membrane to inner ear

• Malleus lateral process & handle attached to TM, head articulates with body of incus
• Incus articulates via long process to stapes
• Food plate of stapes sits in oval window

Question 11

Muscles of middle ear

Answer 11

• Tensor tympani (V_c) → malleus
• Stapedius (VII) → stapes

Both act to modify the transmission of sound waves

Question 12

Blood and nerve supply to the middle ear

Answer 12

Branches of IC & maxillary arteries

CN IX via tympanic plexus

Question 13

Connections of the middle ear

Answer 13

• Anteriorly: auditory tube → nasopharynx
  
  • Medial part cartilaginous, lateral part bony
• Posteriorly: aditus → mastoid antrum
  
  • Only thin bone separating from posterior cranial fossa: cerebellum, temporal lobe & sigmoid sinus

Question 14

Describe the internal ear

Answer 14

Contains the sense organs for hearing of balance, consisting of osseos labyrinth

Question 15

Parts of the osseous labyrinth

Answer 15

Contains the membranous labyrinth

• Vestibule: static equilibrium
  
  • Utricle & saccule
• Semicircular ducts (within canals): dynamic eq.
• Cochlear duct: organ of hearing

All supplied by CN VIII

Question 16

Discuss otitis media

Answer 16

Middle ear infection

• Before antibiotics, could form mastoid abscesses
  
  • Due to thin bone of mastoid air cells, could invade into brain: affect sigmoid sinus, cerebellum & temporal lobe
    
    • Meningitis or cerebral abscesses
• Common in childhood: short/fat auditory tube
  
  • Infection spread from nasopharynx
• Tympanic membrane can rupture in severe cases

Question 17

Discuss hearing loss

Answer 17

• Conduction or sensory organs/neuronal defects
  e. g. acoustic neuroma:
• Benign schwannoma of CN VIII
  
  • Sensorineural deafness & balance/gait problems
• Most common tumour at cerebellopontine angle
• Surgery - translabyrinthine approach - safe but destroys hearing on affected side & risk VIII