Ear

Question 1

describe the innervation of the auricle

Answer 1

Question 2

describe the innervation of the tympanic membrane

Answer 2

• external surface = auriculotemporal nerve (V3) except for a small area via VII and X
• internal surface is by the tympanic plexus (IX)

Question 3

describe the middle ear

Answer 3

• air filled cavity in the petrous part of the temporal bone

Question 4

name the middle ear boundaries

Answer 4

• roof (tegmen tympani): separates cavity from middle cranial fossa
• floor: base of skull near jugular foramen
• anterior wall: separates cavity from carotid canal
• posterior wall: separates cavity from mastoid air cells
• medial wall: separates cavity from inner ear
• lateral wall: mainly tympanic membrane

Question 5

descirbe the lateral wall of the middle ear

Answer 5

• primarily tympanic membrane with handle of meatus
• chorda tympani n. between malleus handle and incus
• tensor tympani tendon attached to handle of meatus

Question 6

describe the medial wall of the middle ear

Answer 6

• oval window and round window
• promontory (with tympanic plexus)
• boney prominences for facial n. and lateral semicircular canal
• tympanic plexus formed by:
  
  • tympanic n. (from CN IX): carries sensory afferents from entire middle ear region and preganglionic PS destined for parotid gland (lesser petrosal n. to synapse at otic ganglion)
  • internal carotid plexus branches: sympathetic fibers to middle ear region

Question 7

describe Bell’s palsy

Answer 7

• lower motor neuron lesion of the facial nerve

Question 8

describe the development of the internal ear

Answer 8

• the otic vesicle derived from the ectoderm will give rise to the membranous labryinth
• the otic vesicle induces the surrounding mesenchyme to condense and differentiate into a cartilaginous otic capsule
  
  • the cartinlaginous otic capsule undergoes ossification to form the bony labyrinth (cochlea, vestibule, semicircular canals)

Question 9

describe the development of the middle ear

Answer 9

• develops from the distal expanded part of the tubotympanic recess arising from the 1st pharyngeal pouch

Question 10

describe the formation of the tympanic membrane

Answer 10

• tympanic membrane develops from the 1st pharyngeal (branchial) membrane
• derived from 3 germ layers:
  
  • ectoderm of the 1st groove
  • endorderm of the 1st pouch
  • mesoderm invades in between

Question 11

describe the development of the auricle

Answer 11

• ear develops from 6 auricular hillocks
  
  • 3 from 1st arch
  • 3 from 2nd arch mesenchyme tissue
• malformation can lead to auricular sinuses and cysts

Question 12

auricular sinuses/pits are present anterior the auricle and are remnants of the ___ ___ ___

Answer 12

auricular sinuses/pits are present anterior the auricle and are remnants of the 1st pharyngeal groove