Ear Anatomy and Embrology- LM

Question 1

What is the blood supply of the outer ear?

Answer 1

a. Posterior auricular a. and v.
b. Superficial temporal a. and v.

Question 2

What is the innervation to the outer ear?

Answer 2

a. Great auricular (C2,C3) and lesser occipital (C2,C3) nn
b. Auriculotemporal nerve (V3), facial n., vagus n.

Question 3

What part of the EAM is bony?

What is the blood supply to the EAM?

Answer 3

1. Lateral 1/3 is cartilaginous; medial 2/3 is bony
2. Blood supply
   a. Posterior auricular a. and v.
   b. Superficial temporal a. and v.
   c. Deep auricular a

Question 4

What is the innervation to the EAM?

What is an important point to remember about the EAM in peds?

Answer 4

auriculotemporal and vagus

The cartilage part of EAM isnt fully formed so you must be careful or use a different otoscope tip

Question 5

What is the function of the TM?

Answer 5

convert sound waves into vibrations of middle ear ossicles

Question 6

The TM is concave from its external view, what causes this?

Answer 6

Malleus

Question 7

The TM has a Pars flaccida and pars tensa, which one vibrates for hearing?

Answer 7

Pars tensa- inferior thick walled portion that vibrates.

Question 8

What is the blood supply to the TM external and internal surfaces?

Answer 8

Deep auricular branch of maxillary for external

Anterior tympanic branch of maxillary for internal

Question 9

What innervates the external surface of TM?

Internal surface?

Answer 9

Auriculotemporal nerve V3 and Vagus

Glossopharyngeal

Question 10

Mesenchyme of the 1st and 2nd pharyngeal arches forms what?

Answer 10

auricle

auricular hillocks will later fuse to form the definitive auricle.

Question 11

What are pits and appendiges on the ears associated with?

Answer 11

Chromosomal defects/syndromes

Question 12

Now some embryology, the first pharyngeal cleft forms something what is it?

Answer 12

EAM

Question 13

Persistence of the meatal plug can cause deafness, when does it degenerate?

Answer 13

by 7th month

Question 14

The TM has three layers and external epithelium, middle connective tissue and internal epithelium, what are they derived from?

Answer 14

External- ectoderm of 1st pharyngeal cleft.

Middle- mesoderm of 1st arch

Internal endoderm of 1st pouch

Question 15

What is the function of the middle ear?

Answer 15

1. Transfer of sound waves from gas to liquid medium(from external to internal ear).
2. Amplification of sound waves via vibration of bony ossicles.
3. Pretective response to loud sounds (via tnesor typani and stapedius mm)

Question 16

What part of the tympanic cavity does the tegmen tympani form?

Answer 16

Roof

Question 17

What is the floor of the tympanic cavity?

Answer 17

Temporal bone separating middle ear from internal jugular.

Question 18

The TM is the lateral wall of the cavity, what is the medial wall?

This medial wall has a promontory, what forms this?

Answer 18

Bony wall separating middle from inner ear.

the cochlea

Question 19

What is the function of the oval window that sits in the medial wall?

Round window?

Answer 19

1. Opens to vestibule of internal ear.
2. Contacted by the stapes; transmits motion of stapes to fluid of internal ear.
3. Opens to scala tympani; covered with a thin membrane (round window membrane)
4. Acts as a pressure release valve for the fluids of the internal ear.

Question 20

We already learned that the temporal bone formed the floor of the tympanic cavity, what other wall does it form?

Answer 20

Posterior

Question 21

Within the posterior wall there is an an opening called aditus ad antrum, what is its significance?

Answer 21

It is the entrance to the mastoid antrum,

a.Mastoiditis. Middle ear infections can sometimes spread to the mastoid air cells. Infections can then spread superiorly into the middle cranial fossa.

These infections are very hard to treat and CAN SPREAD TO MENINGES

Question 22

Floor and posterior wall are temporal bone but wait there is another wall that is too, what is it? What does it seperate the middle ear from?

Answer 22

Anterior wall- separating middle ear from carotid canal. Receives opening for pharyngotympanic tube (auditory tube) and semi-canal (passage of tensor tympani).

Question 23

What does the auditory tube connect?

What is its makeup (1/3 and 2/3 hint)

Function?

Answer 23

1. Cartilaginous and membranous tube connecting middle ear and nasopharynx.
2. Function – balances pressure on external and internal sides of tympanic membrane.
3. Posterolateral third is bony; anteromedial 2/3 is cartilaginous.

Question 24

What muscle can open the auditory tube?

Bonus points what is its innervation?

Answer 24

1.Tensor veli palatini muscle can open the membranous tube (CN V3 innervation)

Question 25

I have confidence that you know the 3 auditory ossicles so tell me what the malleus contacts and its function?

Answer 25

a. Contacts tympanic membrane; creates umbo. b. Vibrates in response to movement of the tympanic membrane.

Question 26

The base of the stapes contacts what structure? What is its function?

Answer 26

a. contacts oval window. b. Vibration of stapes induces motion of the fluid within the cochlear duct.

Question 27

If someone can name the muscles of the inner ear and their innervation I will give them a cookie, (first try only though, be honest)

Answer 27

Stapedius, Facial nerve SVE Tensor Tympani V2 SVE

Question 28

While you eat the cookie you won your chewing sounds like a freight train in your head, what happened?

Answer 28

1.Paralysis of middle ear muscles can cause hyperacusis (excessive hearing acuteness) due to loss of dampening.

Question 29

There are 5 arteries that supply the middle ear but only one venous drainage, take a stab? Hint put tympanic in the name.

Answer 29

1. Inferior tympanic a (from ascending pharyngeal a) 2. Anterior tympanic a (from maxillary a) 3. Posterior tympanic a (from stylomastoid a.) 4. Superior tympanic (from middle meningeal a.) 5. Artery of pterygoid canal (tubal branches to pharyngotympanic tube). 6. Venous drainage to ptergyoid plexus

Question 30

CN IX provides GVA and GVE-P to the middle ear and beyond, what is that pathway? Spend some time on this making sure you have it, Dr Funk loves the nerve pathways.

Answer 30

a. Tympanic branch (GVA; GVE-P) – enters middle ear via tympanic canaliculus; forms tympanic plexus on promontory of tympanic cavity. b. The tympanic plexus provides sensory (GVA) and GVE-P innervation for the middle ear and pharyngotympanic tube. c. Lesser petrosal nerve reforms from tympanic plexus and exits middle ear via the hiatus for the lesser petrosal nerve (GVE-P).

Question 31

Damage to the middle ear could have an effect on what gland

Answer 31

RECALL – Lesser petrosal is the source of parasympathetic innervation to the parotid gland.

Question 32

CN VII supplies SVE to what muscle in the ear and gives off chorda tympani in the process. What is its course? This is a thinker, remember your foramen and what portions of the nerve exit where.

Answer 32

a. Supplies motor innervation to stapedius (SVE) b. Enters internal acoustic meatus, courses along roof of inner ear toward middle ear. c. Within middle ear, CN VII travels within the facial canal on posterior wall. d. Chorda tympani is given off right before CN VII exits the middle ear at the stylomastoid foramen; chorda tympani passes between the incus and malleus and then exits the middle ear via the petrotympanic fissure. RECALL – this is the source of SVA to the anterior 2/3rds of the tongue and the source of GVE-P to the submandibular and sublingual glands.

Question 33

How can the middle ear often become inflammed? (Ottis Media)

Answer 33

often due to spread of infection from pharynx via pharyngotympanic tube.

Question 34

Ear infections can cause dry mouth, why?

Answer 34

pathways to salivary glands go through middle ear

Question 35

More embryology, the tympanic cavity and auditory tube are kind pouches right, so they come from a pouch DUH, which one?

Answer 35

1st

Question 36

TEST ALERT, TEST ALERT What structure do the stapes and stapedius m come from?

Answer 36

2nd arch

Question 37

Where do the malleus, incus and tensor tympani come from? Ok brainstorm, what is tensor tympani innervation and you have the answer.

Answer 37

1st arch

Question 38

Congential fixation of the stapes can cause what?

Answer 38

What, I can't hear you, what, deafness.

Question 39

What bone is the internal ear within?

Answer 39

A.Housed within the petrous portion of the temporal bone, the internal ear contains the vestibulocochlear organ involved in balance and hearing.

Question 40

What is the inner ear bony passages filled with? Osseous spiral lamina anchors what to modiolus?

Answer 40

perilymph cochlear duct

Question 41

What are the membranous ducts filled with/ Innervation

Answer 41

Endolymph CN VIII

Question 42

What does the vestibgular portion of CN VIII innervate?

Answer 42

semicircular ducts, utricle, and saccule to carry proprioceptive information (movements of the head) to the brain.

Question 43

Cochlear portion?

Answer 43

cochlear duct to carry information about sound to the brainstem.

Question 44

How is sound produced? Start from external ear.

Answer 44

1. Airways travel down external acoustic meatus causing vibration of tympanic membrane. 2. Motion of the tympanic membrane causes vibration of the three middle ear ossicles. 3. Footplate of stapes contacts oval window and causes movement of the fluid in the inner ear. 4. Movement of fluid in the cochlear duct causes bending of the hair cells imbedded within the spiral organ. 5. Bending of these hair cells initiates signaling events which ultimately lead to propagation of a nerve impulse along the cochlear portion of CN VIII.

Question 45

The inner ear actually forms in the neck, thats right more embryo What does the Membranous labyrinth develop from? Bony labyrinth?

Answer 45

1. Membranous labyrinth develops from otic placode (ectoderm)→ otic pit → otic vesicle 2. Bony labyrinth (vestibule, semicircular canals, cochlea) from surrounding mesenchyme.