Anatomy and Histology of the Ear

Question 1

What gives blood supply to the external ear?

Answer 1

Posterior auricular and branches from superficial temporal

Question 2

What innervates the posterior external ear?

Answer 2

Lesser occipital n and greater auricular n

Question 3

What innervates the middle part of the external ear?

Answer 3

Vagus n and glossopharyngeal n

Question 4

What innervates over the mastoid process?

Answer 4

Facial n

Question 5

What supplies the superior, anterior, inferior, and posterior parts of the tympanic membrane?

Answer 5

Facial n, auriculotemporal (from CN V), vagus n, great auricular n

Question 6

What are the walls of the middle ear?

Answer 6

Roof - tegmental wall
Floor - jugular wall
Lateral - membranous wall
Medial - labyrinthine wall
Posterior - mastoid wall

Question 7

What is the makeup of the external acoustic meatus? What is the makeup of the pharyngotympanic tube?

Answer 7

EAM: distal 2/3 cartilage, proximal 1/3 bony
PT: distal 2/3 bony, proximal 1/3 cartilage

Question 8

What type of epithelium is the pharyngotympanic tube vs external acoustic meatus?

Answer 8

Pseudostratified columnar vs stratified squamous (with ceruminous glands and hair follicles)

Question 9

What innervates the tensor tympani m and stapedius m?

Answer 9

Trigeminal n and facial n

Question 10

What is the stria vascularis?

Answer 10

Lateral wall of scala media, source of endolymph

Question 11

What is the scala vestibuli continuous with?

Answer 11

The scala tympani

Question 12

What does the stapes move at the oval window?

Answer 12

The perilymph in the scala vestibuli

Question 13

What is connected to the round window?

Answer 13

The scala tympani

Question 14

Where is the organ of corti located?

Answer 14

On the floor of the scala media resting on the basilar membrane

Question 15

When hair cells in the organ of corti are activated what happens?

Answer 15

They send a signal to the spiral ganglion

Question 16

What is the path of sound waves in the inner ear?

Answer 16

Stapes moves oval window (connected to scala vestibuli). Perilymph in scala vestibuli vibrates which acts on vestibular membrane which vibrates endolymph in scala media. Endolymph vibrates basilar membrane which distorts sterocilia of hair cells. Pressure in perilymph is transferred to scala tympani and exits via round window

Question 17

What do the semicircular canals do?

Answer 17

Sense rotational velocity. The anterior canal is in the saggital plane, posterior is in coronal plane, the transverse canal is in the horizontal plane

Question 18

How do the semicircular canals work?

Answer 18

They have an ampulla at the base that contains a cupula with hair cells inside of it. When the cupula is moved due to head rotation/acceleration the endolymph pushes the cupula (in the opposite direction) which distorts the hair cells

Question 19

How do the utricle and saccule work?

Answer 19

They are within the vestibule and both contain a macula - hair cells with stereocilia with overlying gelatinous material called otolithic membrane. Otolithic membrane covered with rocks that sense gravity and linear acceleration

Question 20

What does the utricle detect?

Answer 20

Linear acceleration

Question 21

What does the saccule detect?

Answer 21

Gravity/which way is up

Question 22

What happens when stereocilia bend toward kinocilium?

Answer 22

K+ channels open causing depolarization

Question 23

What happens when stereocilia bend away from kinocilium?

Answer 23

K+ channels close causing hyperpolarization

Question 24

What drugs target/damage hair cells?

Answer 24

Aminoglycosides and loop diuretics

Question 25

What produces perilymph?

Answer 25

Periosteum

Question 26

What produces endolymph

Answer 26

Stria vascularis

Question 27

What is cauliflower ear?

Answer 27

Can occur in wrestling when perichondrium separates from elastic cartilage layer. Can cause hematoma or necrotic cartilage

Question 28

What is mastoiditis?

Answer 28

Infection of mastoid cells, can spread into cranial fossa via petrosquamous cranial suture

Question 29

What is otitis media?

Answer 29

Infection of middle ear, very common. Fluid or puss in middle ear due to infection or inflammation

Question 30

What is Meniere’s syndrome?

Answer 30

Increased endolymph increases pressure of membranous labyrinth, limits movement and sensitivity of hair cells

Question 31

What is viral labyrinthitis?

Answer 31

Same as Meniere’s syndrome but resolves within a week