Ear

Question 1

How is the internal ear developed?

Answer 1

Via otic placodes (thickening of surface endoderm that invaginate creating otic vesicles)

Question 2

How are Vesicles developed?

Answer 2

Cells differentiate to form ganglion cells for CN VIII

Forms membranous labyrinth where the ventral part forms saccule and cochlear duct and the dorsal part forms the utricle, semicircular ducts, and endolymphatic duct

Question 3

How does the middle ear develop?

Answer 3

Endoderm from the 1st pharyngeal pouch

Tubotympanic recess (distal part of 1st pouch) expands to form the tympanic cavity

Proximal 1st pouch forms the auditory tube

Question 4

How are ossicles developed?

Answer 4

1st Arch: Malleus and Incus
2nd Arch: Stapes

Stays in mesenchyme until 8th month

Question 5

How does the external ear develop?

Answer 5

1st Pharyngeal cleft: External Acoustic Meatus

Auricle: develop from 6 auricular hillocks derived from 1/2 pharyngeal arches and 1st cleft

Question 6

What does the Auricle do?

Answer 6

Collect sound and funnels it to the external acoustic meatus

Question 7

What is the auricle made of?

Answer 7

elastic cartilage

Question 8

What is defected in auricular abnormalities?

Answer 8

Neural crest defects

Question 9

What is the sensory innervation of the auricle?

Answer 9

Auriculotemporal nerve (V3): Anterior ear
Cervical Plexus (C2-C3): Posterior Ear
Facial and Vagus Nerves: Inside the Auricle

Question 10

What is Otitis Externa?

Answer 10

Swimmer’s Ear where the external acoustic meatus is inflamed due to bacterial infection

Question 11

What does the tympanic membrane do?

Answer 11

1. Separates external acoustic meatus from middle ear
2. Vibrates in response to sound and transmits this to the ossicles

Question 12

What innervates the tympanic membrane?

Answer 12

Outer surface: Auriculotemporal nerve and Auricular branch of the vagus nerve.
Inner surface: Glossopharyngeal nerve

Question 13

What can cause a ruptured eardrum?

Answer 13

Otitis media, foreign bodies, trauma, and pressure

Question 14

What are the ossicles?

Answer 14

Malleus, Incus, and Stapes

Question 15

What muscles and their innervations are in the middle ear?

Answer 15

Tensor Tympani: V3
Stapedius: Facial Nerve

Question 16

What is a stepedius reflex?

Answer 16

Contractions of the stapedius muscles in response to a loud noise. helps protect the inner ear from damage

Question 17

What does the pharyngotympanic tube connect?

Answer 17

Tympanic cavity to the nasopharynx

Question 18

What does the pharyngotympanic tube do?

Answer 18

Equalizes pressure in the middle ear with atmospheric pressure

Question 19

What muscles help open the pharyngotympanic tube up and equalize pressure?

Answer 19

Tensor veli palatini and levator veli palatini

Question 20

What is Otitis Media?

Answer 20

Middle Ear Infection

Question 21

What is the pathway of the facial nerve?

Answer 21

1. Enters skull via internal acoustic meatus
2. Geniculate ganglion (sensory cell bodies for taste of anterior 2/3 tongue)
3. Greater petrosal nerve branch: comes off of geniculate ganglion
4. Nerve to stapedius branch: branches off in facial canal
5. Chorda tympani branch: passes through middle ear between malleus and incus
6. Exits skull via stylomastoid foramen