Ear

Question 0

Describe features of the middle ear

Answer 0

Air filled chamber in petrous part of temporal bone

• Tympanic cavity proper is connected to nasopharynx by Eustachian tube and mastoid air cells by mastoid antrum
• Epitympanic recess is the space above the tympanic membrane

Eustachian tube is usually closed but is opened when swallowing to allow equalisation of pressure

• Auditory ossicles (malleus, incus and stapes) articulate via synovial joints.
• Malleus is controlled by tensor tympanii CN IV, attached to tympanic membrane whilst Stapes is controlled by stapedius CN VII and articulates with boney labyrinth at oval window. Both act to dampen sound with loud noises.

Facial nerve passes through facial canal, separated by thin bone from tympanic cavity, thus middle ear infection may case CN VII lesion

Question 1

Describe the features of the external ear

Answer 1

Auricle (pinna)
- irregular shape (elastic cartilage)
- outer rim (helix), tragus and anti tragus
- non cartilaginous lobule
- external carotid artery supplies posterior auricular artery and superficial temporal artery
Sensation: anterior- auriculotemporal nerve CN V3
Posterior- great auriculotemporal nerve

External acoustic meatus (canal)

• 1/3 cartilage, 2/3 boney tube
• lies in temporal bone (secretes cerumen)
• sigmoid shaped (adults: pull up/back, kids: pull down)

Tympanic membrane
- thin oval, transparent grey membrane
- separates external/middle ear
Sensation: external- auriculotemporal and vagus nerve
Internal- glossopharyngeal nerve

Question 2

Describe features of inner ear

Answer 2

Inner ear (transducer) is within petrous temporal bone, surrounded by membranous labyrinth

• vestibule is a sac containing endolymph, involved in balance: sensitive to rotational acceleration and pull of gravity
• semicircular ducts and canals contains receptors that respond rotational acceleration
• cochlear end organ is a sac containing perilymph involved in hearing. Shell shaped boney labyrinth containing cochlear duct, (houses organ of corti- auditory receptors)

Question 3

Discuss problems associated with the ear

Answer 3

1. Pinna deformities: cauliflower ear and pinna haematoma
2. Bulging, perforated and retracted tympanic membrane with infections
3. Middle ear infections (otitis media) can lead to mastoiditis and effusion (glue ear: grommets allow fluid to drain)
4. Blocked Eustachian tube can lead to cholestoma and conductive hearing loss
5. Benign positional paroxysmal vertigo: stones in vestibule causing overstimulation and prolonged sensation of movement
6. Menieres syndrome: XS fluid in vestibule
7. Sensoneurial hearing loss: defect in pathway from cochlear to brain