Ear Anatomy

Question 1

What is the pterion?

Answer 1

This is the thinnest part of the skull formed by an H-shaped suture between the frontal, parietal, temporal and sphenoid bone. FUN FACT: it has been referred to as ‘gods joke’ as the middle meningeal artery runs right behind this and damage will result in epidural haematoma.

Question 2

What are the 2 parts to the temporal bone?

Answer 2

squamous (smooth) part

Petrous (rocky) part.

Question 3

This is a diagram of the base of the skull, what are the 3 regions called and which bones are contained within each?

Answer 3

Anterior cranial fossa - frontal bone, ethmoidal and sphenoid

Middle cranial fossa - sphenoid and temporal (squamous and petrous)

Posterior cranial fossa - temporal (petrous) and occipital

Question 4

Where does each cranial nerve exit the skull?

Answer 4

CN 1 = cribiform plate of ethmoid bone

CN 2 = optic canal

CN 3 = superior orbital fissure (SOF)

CN 4 = SOF

CN 5 (opthalmic) = SOF

CN 5 (maxillary) = foramen rotundum

CN 5 (mandibular) = foramen ovale

CN 6 = SOF

CN 7 and 8 = internal acoustic meatus

CN 9, 10 and 11 = jugular foramen (along with internal juglar vein)

CN 12 = hypoglassal canal

Question 5

These are the areas of the ear, describe their boundaries.

Answer 5

External = auricle to tympanic membrane via the external acoustic meatus

Middle = Tympanic membrane to oval window (also contains the eustachian tube)

Internal = oval window to internal acoustic meatus.

Question 6

What are the functions of the 3 areas of the ear?

Answer 6

External - collects and conveys sound waves to the tympanic membrane

Middle - amplifies and conducts the sound waves to the inner ear

Internal - converts the sensory information into fluid waves, then APs then sent to brain.

Question 7

Where do cranial nerve 2 and 3 supply?

Answer 7

the external ear (auricle)

Question 8

What does CN V3 supply on the external ear?

Answer 8

supplies the superior aspect of the external auditory meatus and superior 2/3 of the tympanic membrane

Question 9

What does CN X supply on the external ear?

Answer 9

Inferior parts of the external auditory meatus and inferior part of the tympanic membrane.

Question 10

What is the lyphatic drainage of the auricle?

Answer 10

Lateral part of superior = partotid nodes

Cranial surface of superior = mastoid

Rest of auricle = superficial cervical nodes

these all eventually drain to deep cervical and to the venous angle.

Question 11

What produces earwax and where do these reside?

Answer 11

ceruminous glands in the ear canal

Question 12

What is the skelton of the ear?

Answer 12

Elastic cartilage (avascular) and petrous part of the temporal bone

Question 13

What does the glossopharyngeal nerve innervate?

Answer 13

Middle ear, eustachian tube, nasopharynx, oropharynx and tonsils.

Question 14

What are the three auditory ossicles are where are they?

Answer 14

These are the 3 bones in the middle ear:

Malleus

Incus

Stapes

All three articulate via synovial joints and help to conduct sound waves to the internal ear.

Question 15

What is the umbo and how is it formed?

Answer 15

This is the most inward pulled part of the tympanic membrane and is formed by the horn of the malleus pulling it inward.

Question 16

How is sound amplified and conducted to the internal ear?

Answer 16

Sound waves cause vibration of the tympanic membrane which will cause vibration of the malleus. As all three bones articulate, the vibration is passed along. At the vibration reaches the stapes bone it causes tapping against the bony surface of the ‘oval window’

Question 17

What is the eustachian tube and what is its function?

Answer 17

This is a tube that connects the middle ear to the nasopharynx.

It is thought to be there to help equalise air pressures.

Question 18

What is important clinically about the eustachian tube?

Answer 18

It is not uncommon for bacteria and viruses to spread via this tube to result in pain and hearing loss.

Question 19

What are the functions of the facial nerve?

Answer 19

Special sensory - taste (supplies first 2/3rds of tongue)

Sensory - Face

Motor - muscles of facial expression

Parasympathetic - supplies the submandibular and sublingual salivary glands (as well as lacrimal)

Question 20

Which nerve runs through the internal auditory canal?

Answer 20

CN 7

Question 21

What is the function of the stapedius muscle?

Answer 21

this is the smallest skeltal muscle that controls the stapes in times of loud noise so as not to cause damage to the inner ear.

Question 22

How would you test for a facial nerve palsy?

Answer 22

ask the patient to frown, smile, close eyes tightly and puff out cheeks.

Question 23

Where is the internal ear located and what is its function?

Answer 23

in the petrous part of the temporal bone and its function is to convert vibrations to special sensory information

Question 24

How is the vestibulocochlear nerve split (CN 8)?

Answer 24

Vestibular branch - balance

Cochlear branch - hearing

Question 25

What is the otic capsule?

Answer 25

This is a capsule of bone that is denser than the surrounding petrous temporal bone. It contains the bony labyrinths (spaces in the bone that are fluid filled - with perilymph)

Question 26

What is suspended within the perilymph of a labyrinth?

Answer 26

sacs and ducts which make up the membranous labyrinth and is filled with endolymph.

Question 27

What is the function of the fluid?

Answer 27

The movement of the fluid helps with hearing (cochlea) and balance (in the semi-circular canals)

Question 28

How are these fluid movements transported to the brain?

Answer 28

Via the cochlear and vestibular branches of CN 8 (which joins to become one in the internal acoustic meatus).

Question 29

What would some symptoms associated with internal acoustic meatus pathology be?

Answer 29

CN 7 = facial nerve palsy, dry mouth and eyes, loss of taste, loss of sensation to facial muscles

CN 8 = loss of hearing and balance