Lecture 15: Anatomy of the Ear

Question 1

What is the major blood supply to the pinna of ear both anteriorly and posteriorly?

Answer 1

• Blood supply from ECA
• Anteriorly supplied by the Superficial Temporal A.
• Posteriorly supplied by the Posterior Auricular A.

Question 2

How does the cartilage of the ear receive its blood supply and why is this clinically significant?

Answer 2

• From the perichondrium
• If this blood supply is compromised you can get necrosis and inflammation of the cartilage
• Eventualy leading to deformity of the ear, i.e., Cauliflower ear

Question 3

What innervates the different areas of the external ear (anterior, concha, and posterior margin)?

Answer 3

Anterior: auriculotemporal n. (trigeminal CN V)

Concha: Vagus n. and glossopharyngeal n.

Posterior margin: Lesser occipital and greater auricular (cervical plexus)

Question 4

What is the lymph drainage from the ear like both anteriorly and posteriorly?

Answer 4

Anteriorly: drains into the inter-parotid nodes

Posteriorly: drains into the jugulodigastric nodes

Question 5

What provides sensory innervation to the mucosal layer of the tympanic membrane?

Answer 5

Glossopharyngeal CN IX

Question 6

What can cause someone to cough when wax is irritating their ear?

Answer 6

• The Vagus nerve innervates part of the external auditory canal
• Specifically the posterior/floor region where wax gets trapped

Question 7

Which portion of the Tympanic membrane is most susceptible to retraction from differences in middle ear pressure?

Answer 7

• The Pars Flaccida
• Fairly fragile because it does not contain the rigid and radial circular fibers like teh Pars Tensa does

Question 8

What are the 2 things that you will see on the anterior wall of the middle ear cavity?

Answer 8

• Eustachian tube
• Tensor Tympani muscle

Question 9

What is seen on the lateral wall of the middle ear cavity?

Answer 9

• Large bump known as the promontory
• Promontory is the basal turn of the cochlea, the LARGEST turn in the organ
• Facial n.
• Lateral semi-circular canal
• Stapes

Question 10

What is seen coming out of the floor of the middle ear and where is it going?

Answer 10

• The tympanic nerve, branch of CN IX, which goes to the tympanic plexus
• After merging with tympanic plexus becomes the lesser superficial petrosal nerve where it controbutes efferents to the otic ganglion

Question 11

What is seen posteriorly in the middle ear cavity?

Answer 11

A pyramidal process which contains the tendon of the Stapedius muscle, which attaches to the posterior crus of the Stapes

Question 12

Embryologically what are the 2 parts of the middle ear cavity, which arch is each from?

Answer 12

1) Mesotympanum (middle/lower) from the 2nd pharynheal arch
2) Epitypanum (attic) from the 1st pharyngeal arch

Question 13

What is the only bone found in the mesotympanum of middle ear; what other parts?

Answer 13

• Stapes
• Long process of Incus
• Handle of Malleus

Question 14

What is found in the epitympanum of middle ear?

Answer 14

• Head of Malleus
• Body of the Incus

Question 15

How does the eustachian tube change from childhood to adulthood and why is this significant?

Answer 15

• In children is almost horizontal so gravity is not able to act on it to drain middle ear; more prone to infections
• In adults the tube will be at a much more favorable angle for drainage

Question 16

Describe the course of the facial nerve (each segment) as it moves through the Temporal bone/ear?

Answer 16

1) First portion is internal auditory segment and after first turn it will give off the superficial petrosal nerve
2) Next course through tympanic segment, running behind the ossicles
3) Makes another turn and dives straight into mastoid bone, becoming the mastoid segment
4) Last, it comes out the stylomastoid foramen and becomes facial nerve proper before entering the parotid gland

Question 17

What does the superior vestibular nerve versus inferior vestibular nerve innervate inside the ear?

Answer 17

Superior vestibular: superior canal, horizontal canal, and superior portion of vestibule (the utricle)

Inferior vestibular: innervates the saccule and posterior semi-circular canal

Question 18

The utricle and saccule allow us to detect which motion?

Answer 18

Horizontal and vertical motions

Question 19

Distortion of the cupula and macula give us what type of sensation?

Answer 19

Rotary sensation

Question 20

The fluid within the Scala Vestibuli is directly stimulated by what; what does the Scala Tympani move?

Answer 20

• Scala Vestibuli is directly stimulated by the movement of the Stapes
• The Scala Tympani is what moves the round window

Question 21

When fluid inside the compartments of the Scala Vestibuli and Scala Tympani move what does this lead to?

Answer 21

• Changes the movement of the Tectorial Membrane and its relation to the Outer and Inner Hair cells
• This shift causes depolarization of these cell types

Question 22

Where are high frequency versus low frequency sounds heard within the cochlea?

Answer 22

• High frequency sounds are detected near the base of the cochlea
• Low frequency sounds are detected further into the cochlea near the apex

Question 23

What happens to hair cells as you move into the cochlea, what does this do to the angle?

Answer 23

• The lower you go in the cochlea the number of hair cells begins to decrease
• This makes the angle become steeper
• Allows for lower frequency sounds to be heard better near the apex of the Cochlea

Question 24

What nerves provide the sensory innervation to external portion of external tympanic membrane?

Answer 24

• CN V
• CN VII
• CN X

Question 25

What innervates the Stapedius m. and the Tensor Tympani m.?

Answer 25

- Stapedius by CN Seven; Facial n.

• Tensor Tympani by Trigeminal; CN IX