Ear

Question 1

External Acoustic Meatus

Answer 1

Tube that extends from the deep part of the concha to the tympanic membrane.

Question 2

Tympanic Membrane

Answer 2

It is a connective tissue structure, at the end of the external acoustic meatus, covered with skin on the outside and a mucous membrane on the inside.

Question 3

Walls of the external acoustic meatus

Answer 3

External 1/3 are formed by cartilage, whereas the inner 2/3 are formed by the temporal bone.

Question 4

What attaches to the tympanic membrane?

Answer 4

Handle of malleus attaches to the tympanic membrane, at a point called the umbo of tympanic membrane.

Question 5

What innervates the skin of the auricle?

Answer 5

Greater auricular nerve (branch of the cervical plexus) Lesser occipital nerve (branch of the cervical plexus)

Question 6

What innervates the skin of the auricle and external auditory meatus?

Answer 6

Auriculotemporal nerve (branch of the mandibular V3 nerve)

Question 7

What innervates the deeper aspect of the auricle and external auditory meatus?

Answer 7

Branches of the facial and vagus nerves

Question 8

Auditory ossicles

Answer 8

Malleus, incus and stapes

Question 9

What does each ossicle join to?

Answer 9

Malleus (tympanic membrane to incus)
Incus (malleus to stapes)
Stapes (incus to oval window)

Question 10

What are the two muscles which serve a protective function in the middle ear?

Answer 10

Tensor tympani and stapedius.

Question 11

What is the function of the middle ear muscles?

Answer 11

They contract in response to loud noise (own voice), inhibiting the vibrations of the malleus, incus and stapes, and reducing the transmission of sound to the inner ear. This action is known as the acoustic reflex.

Question 12

Where do the middle ear muscles attach?

Answer 12

Tensor tympani originates from the auditory tube and attaches to the handle of malleus, pulling it medially when contracting.

Stapedius is attached to the stapes

Question 13

What innervates the middle ear muscles?

Answer 13

Tensor tympani is innervated by the tensor tympani nerve, a branch of the mandibular nerve V3.

Stapedius is innervated by the facial nerve.

Question 14

What is hyperacusis associated with and why?

Answer 14

Associated with facial nerve palsies which cause loss of the ear’s protective stapedial reflex.

Question 15

What is the eustachian tube?

Answer 15

Cartilaginous and bony tube that connects the middle ear to the nasopharynx. It acts to equalise the pressure of the middle ear to that of the external auditory meatus.

Question 16

Bony labyrinth

Answer 16

Consists of a series of bony cavities within the petrous part of the temporal bone. It is composed of the cochlea, vestibule and three semi-circular canals.

Question 17

Vestibule

Answer 17

Central part of the bony labyrinth.

It is separated from the middle ear by the oval window, and communicates anteriorly with the cochlea and posteriorly with the semi-circular canals.

Question 18

Cochlea

Answer 18

Auditory part of the inner ear.

It spirals forming a central modiolus, branches from the cochlear portion of the vestibulocochlear (VIII) nerve are found at the base of the modiolus.

Extending outwards from the modiolus is a ledge of bone known as spiral lamina.

Question 19

Semi-circular Canals

Answer 19

There are three semi-circular canals: anterior, lateral and posterior. They contain the semi-circular ducts, which are responsible for balance (along with the utricle and saccule).

Question 20

What parts of the membranous labyrinth are located in the vestibule?

Answer 20

Two parts of the membranous labyrinth; the saccule and utricle, are located within the vestibule

Question 21

Membranous labyrinth

Answer 21

Lies within the bony labyrinth. It consists of the cochlear duct, semi-circular ducts, utricle and the saccule. The membranous labyrinth is filled with fluid called endolymph.

Question 22

Cochlea duct

Answer 22

The presence of the cochlear duct (scala media) creates two perilymph-filled chambers above and below

Scala vestibuli: Located superiorly to the cochlear duct. As its name suggests, it is continuous with the vestibule.

Scala tympani: Located inferiorly to the cochlear duct. It terminates at the round window.

Question 23

Semi-circular Ducts

Answer 23

The semi-circular ducts are located within the semi-circular canals, and share their orientation.

Upon movement of the head, endolymph flows within ducts and changes speed and direction, sensory receptors in the ampullae detect this and signal to brain

Question 24

Saccule and Utricle

Answer 24

The saccule and utricle are two membranous sacs located in the vestibule.

They are organs of balance which detect movement or acceleration of the head in the vertical and horizontal planes, respectively.

Endolymph drains from the saccule and utricle into the endolymphatic duct.

Question 25

Vestibular nerve passage

Answer 25

Enlarges to form the vestibular ganglion, which then splits into superior and inferior parts to supply the utricle, saccule and three semi-circular ducts.

Question 26

Cochlear nerve passage

Answer 26

Enters at the base of the modiolus and its branches pass through the lamina to supply the receptors of the Organ of Corti.