Anatomy and Embryo: Ear

Question 1

auricle

Answer 1

collects airwaves and funnels them into external acoustic meatus
- made of elastic cartilages, lobules and depressions

Question 2

blood supply to auricle?

Answer 2

post auricular a/v

superficial temporal a/v

Question 3

innervation to auricle?

Answer 3

• Great auricular and lesser occipital nn (C2,3)
• auriculotemporal n (V3), facial n, vagus n.
• lymph drains to mastoid, parotid lymph nodes and to deep cervical lymph nodes

Question 4

external acoustic meatus

Answer 4

canal traveling through tympanic portion of temporal bone to tympanic membrane

• lined by stratified squamous
• lateral 1/3 cartilaginous, medial 2/3 bony

Question 5

blood supply to external acoustic meatus

Answer 5

post. auricular a/v

superficial temporal a/v

Question 6

innervation to external acoustic meatus

Answer 6

auriculotemporal n (V3)
Vagus n.
all lymph drains to deep cervical nodes

Question 7

otitis externa

Answer 7

inflammation of external ear

Question 8

tympanic membrane

Answer 8

• converts sound waves into vibrations of middle ear ossicles.
• fibroelastic membrane, connected to malleus.
• covered externally by epidermis and internally by mucus membrane
• membrane is anterior and inferior

Question 9

blood supply to tymp. membrane?

Answer 9

external surface: deep auricular branch of maxillary a.

internal surface: anterior tymp. branch of maxillary a.

Question 10

innervation to tymp membrane?

Answer 10

external surface: auriculotemporal n (V3), vagus n.

internal surface: glossopharyngeal n. (endodermally derived)

Question 11

how does auricle develop?

Answer 11

derived from cartilage of 1st/2nd pharyngeal arches

* defects often associated with most chromosomal syndromes *

Question 12

how does external aud. meatus develop?

Answer 12

first pharyngeal cleft

- meatul plug forms, if does not degenerate by 7th month, will cause deafness and congenital hearing loss

Question 13

tympanic membrane development?

Answer 13

external ectoderm= ectoderm of first pharyngeal cleft

middle CT= mesoderm of first pharyngeal arch

internal epithelium = endoderm of first pharyngeal arch

Question 14

fn of middle ear

Answer 14

• contains tympanic cavity, a mucous lined space w/in petrous portion of temporal bone and auditory ossicles.
• fn = transfer of sound waves from gas to liquid medium (from external to internal ear).
• amplifies sound waves in the process via bony ossicles
• protective response to loud sounds (tensor tympani, stapedius mm.)

Question 15

what forms boundaries of tympanic cavity?

Answer 15

roof: tegmen tympani (seperates epitympanic recess from middle cranial fossa)
floor: temporal bone (seperates from IJV)

lateral wall: tymp membrane

medial wall: promontory, oval window, round window

post wall: temporal bone

ant wall: temporal bone

Question 16

what are portions of medial wall?

Answer 16

1. promontory: mound of bone created by cochlea
2. oval window(fenestrae vestibule): opens to vestibule of inner ear: contacted by stapes; transmits motion of stapes to fluid of internal ear.
3. round window (fenestra cochlea): opens to scala tympani; covered with thin membrane: acts as a pressure release valve for fluids of internal ear

Question 17

what does posterior wall contain?

Answer 17

• seperates middle ear from mastoid air cells
• aditus ad antrum = entrance to mastoid antrum
• facial canal = passage of facial n.

Question 18

mastoiditis

Answer 18

• infections of nasopharynx can spread to auditory tube, then into middle ear.
• middle ear infections, can sometimes spread to mastoid air cells
• from mastoid air cells the infections can spread superior into the middle cranial fossa

Question 19

what is contained in anterior wall

Answer 19

• receives opening from pharyngotympanic tube and semi-canal

- tensor tympani passes through here (works to dampen vibrations)

Question 20

pharyngotympanic tube

Answer 20

“auditory tube”

• located in anterior wall
• mucous membrane connects middle ear and nasopharynx
• fn: balances pressure on external and internal sides of tympanic membrane

** tensor veli palatine: mm. attaches to membranous portion of auditory tube and can open the membranous tube via CN V3 (allowing for equalization of inner ear)

Question 21

what are the auditory ossicles?

Answer 21

1. malleus (contacts TM)
2. incus (middle)
3. stapes (contacts oval window)- vibration moves fluid within cochlear duct

• work on an amplification system, all are united by synovial joints

*** osteosclerosis = synovial joints become thick = conductive hearing loss

Question 22

stapedius

Answer 22

= mm. of the inner ear 
O: post wall of tymp. cavity
I: stapes
fn: dampens mvmts of ossicles (contracts reflexively in response to loud noises)
n: facial n - SVE

Question 23

tensor tympani

Answer 23

O: cartilagenous part of pharyngotymp. tube
I: malleus
fn: dampens mvmt of ossicles (contracts when chewing and speaking)
n: trigeminal n (V3) SVE

Question 24

paralysis of middle ear mm?

Answer 24

can cause hyperacusis = excessive hearing acuteness = due to loss of dampening mm.

Question 25

blood supply to Tm?

Answer 25

- inferior tymp (ascending pharyngeal) - ant tymp (maxillary) - post tymp (stylomastoid) - superior tymp (middle meningeal a.)

Question 26

how does CN IX provide the ear?

Answer 26

glossopharyngeal n. -supplies GVA and GVE-P to middle ear - tympanic branch (GVA, GVE-P) enters middle ear via tympanic canaliculus; forms tympanic plexus. - tympanic plexus provides GVA sensory and GVE-P innervation for middle ear. - lesser petrosal n. reforms from tymp. plexus and exits midle ear via hiatus for lesser petrosal n (GVE-P)--> PS to parotid gland

Question 27

how does CN VII supply ear?

Answer 27

supplies motor innervation to stapedius (SVE) - enters internal acoustic meatus, courses along roof of inner ear toward middle ear - within middle ear CN VII travels within facial canal on posterior wall - chorda tympani is given off right before CN VII exitsmiddle ear at stylomastoid m=foramen, corda tympani passes b/w incus and malleus and exits the middle ear via petrotympanic fissure ** corda tympani: provides SVA to ant 2/3 of tongue and GVE-P to submandibular and sublingual glands

Question 28

otitis media?

Answer 28

inflamation of middle ear; often due to spread of infection from pharynx via pharyngotympanic tube

Question 29

what are three branches of facial n. in middle ear?

Answer 29

1. greater petrosal n (GVE-P to pterygopalatine ganglion) 2. n. to stapedius 3. corda tympani (SVA and GVE-P to glands)

Question 30

how is middle ear derived? **TQ**

Answer 30

tympanic cavity and auditory tube = first pharyngeal pouch malleus, incus, tensor tympani: first pharyngeal arch stapes, stapedius = second pharyngeal arch *** congenital fixation of stapes can cause deafness due to problem with 2nd arch ***

Question 31

membranous labyrinth

Answer 31

this is where sound is processed - membranous ducts contained within bony labyrinth that are filled with endolymph (bony labyrinth filled w/ perilymph) - cochlear duct: processes sounds : hair cells are housed in spiral organ

Question 32

Vestibulocochlear n

Answer 32

CN VIII - exits brainstem at pontomedullary jn. - passes through internal acoustic meatus to enter inner ear - vestibular portion innervates semicircular ducts, utricle, saccule, carrying proprioceptive info - cochlear portion innervates coochlear duct and carries info about sound

Question 33

how is inner ear derived?

Answer 33

membranous labyrinth: develops from otic placode (ectoderm) bony labyrinth (vestibule, semicircular canals, cochlea), from surrounding mesenchyme of otic placode