Exam 4 Ear

Question 1

Features of the External Ear

Innervation of External Ear

Answer 1

• Pinna (auricle)
  
  • Helix (Orange)
  • Anithelix (Red)
  • Antitragus (Blue)
  • Tragus (Pink)
  • Scaphoid fossa
  • Concha (Yellow)
  • Lobule (Green)
• External auditory meatus
• Innervation:
  
  • Great auricular nerve (Off cervical plexus)
  • Lesser occipital nerves (Off cervical plexus)
  • Branches of facial nerve
  • Auriculotemporal branch of trigeminal nerve
  • Auricular branch of vagus

Question 2

Tympanic Membrane

• What are its parts?
• What bone can be seen through tympanic membrane?
• What does it separate?

Answer 2

• Parts:
  
  • Pars tensa: Taut portion of membrane
  • Pars flaccida: Looser portion that allows membrane to vibrate against ossicles
• Can see malleus through tympanic membrane
• Separates external ear from middle ear.

Question 3

What is otitis externa?

Answer 3

• AKA Swimmer’s ear
• Infection in ear canal of external ear
• Symptoms include pain and clear discharge.

Question 4

• What is a myringotomy?
• What is it used to treat?
• What can accompany this procedure?

Answer 4

• Surgery to make hole in ear drum
• Used to suction fluid from middle ear behind tympanic membrane
• Tympanostomy tube often accompanies it to allow continual fluid drainage

Question 5

Middle Ear

• Boundaries (Roof, floor, lateral wall, medial wall, anterior wall, posterior wall)
• Bones of the inner ear
  
  • What are they attached to?
• What passes between malleus and incus?

Answer 5

• Boundaries:
  
  • Roof: Tegmen tympani
  • Floor: Jugular wall (separates middle ear from internal jugular vein)
  • Lateral wall: Tympanic membrane
  • Medial wall: Promontory (bulge of temporal bone formed by cochlea)
  • Anterior wall: Carotd wall (eustachian tube opens here)
  • Posterior wall: Mastoid wall (contains aditus going into mastoid antrum and mastoid air cells)
• Bones:
  
  • Malleus: Attached to tympanic membrane
    
    • Anchored by several ligaments and tensor tympani muscle
  • Incus: Between malleus laterally and stapes medially
    
    • Chorda tympani passes between malleus and incus just posterior to tympanic membrane
  • Stapes: Anchored to medial wall
    
    • Attaches to oval window
    • Translates movements of ossicles into pressure waves of cochlea

Question 6

• What is the function of tensor tympani muscle?
• What is the function of stapedius muscle?
• What are their innervations?

Answer 6

• Tensor tympani: Dampens loud sounds by restricting vibratory movements of ossicle in response to movement
  
  • Innervated by CN V3
• Stapedius: Dampens loud sounds
  
  • Innervated by CN VII

Question 7

What is mastoiditis?

Answer 7

• Infection from middle ear can spread into mastoid process via aditus to mastoid antrum.
• Mastoid process hollow and covered with damp mucosa to allow bacteria to grow

Question 8

• What nerves are found in middle ear?
• What are their branches?
• What do they supply?
• How do they enter middle ear?
• How do they exit middle ear?

Answer 8

• Facial nerve
  
  • Enters via internal acoustic meatus
  • Bends at geniculate ganglion to give off great petrosal nerve
  • Gives off nerve to stapedius
  • Gives off chorda tympani that passes through middle ear without innervating anything
  • Exits via stylomastoid foramen
• Glossopharyngeal nerve
  
  • Enters via jugular foramen
  • Tympanic branch of IX supplies sensory to middle ear mucosa and inner surface of tympanic membrane
  • Tympanic branch gives off preganglionic parasympathetics that do not supply anything.
  • Preganglionic parasympathetics join postganglionic sympathetics from internal carotid plexus to form tympanic plexus over promontory
  • Tympanic plexus gives off lesser petrosal nerve to synapse in otic ganglion and go on to supply parotid gland
  • Exits via hiatus of lesser petrosal nerve

Question 9

Bony and membranous labyrinth

• What are they?
• What do they contain?

Answer 9

• Bony labyrinth: Hollowed out areas of temporal bone
  
  • Contains perilymph (White)
• Membranous labyrinth: Lines bony labyrinth (Blue)
  
  • Contains endolymph
  • Organs of hearing and balance float in endolymph

Question 10

Vestibule

• What does it contain?
• What is its function?

Answer 10

• Saccule: Detects vertical acceleration
• Utricle: Detects horizontal acceleration

Question 11

Semicircular canals

• What is their orientation?
• What do they contain?
• What do they sense?

Answer 11

• Three semicircular canals oriented at right angles
• Contain crista in their ampulla
• Sense angular acceleration

Question 12

Cochlea

• Where is it located in relation to vestibule?
• What does it contain?

Answer 12

• Medial from vestibule
• Contains:
  
  • Cochlear duct: Membranous labyrinth of cochlea
  • Scala vestibuli: Upper perilymph filled space separated by cochlear duct
  • Scala tympani: Lower perilymph filled space separated by cochlear duct
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