Ear and Auditory Tube

Question 1

function of auricle in the outer ear?

Answer 1

localization of sound

Question 2

which cranial nerve innervates the outer ear?

Answer 2

vagus nerve (3rd branch: auriculotemporal nerve) innervates the anterosuperior and external surface of tympanic membrane

Question 3

in cases of normal middle ear pressure, shining a light into the external auditory meatus would produce a cone of light in which quadrant of tympanic membrane?

Answer 3

Anteroinferior-quadrant. Deviation from here suggests increase or decrease in middle ear pressure.

Question 4

describe concavity of the tympanic membrane?

Answer 4

concave outwards/laterally. and convex inwards/medially

Question 5

which component of the middle ear permits communication with the nasopharynx? whats the purpose?

Answer 5

auditory/eustachian tube. allows for equalization of middle ear pressure with atm pressure.

Question 6

where are ear infections more common in infants than adults?

Answer 6

in adults, the downward gradient of the eustachian tube into the nasopharynx makes it difficult for bacteria to get into middle ear.
In children, the eustachian tube takes a much straighter path.

Question 7

whats the arrangement of the ossicles from the tympanic membrane

Answer 7

tympanic membrane–>malleus–>incus–>stapes–>oval window

Question 8

how are environmental sounds interpreted by the ear?

Answer 8

incoming sounds will vibrate the occicles (malleus is attached to tympanic membrane and so on) at a rate proportional to the pitch of the incoming sound.

Question 9

why is increased sensitivity to loud sounds a symptom of Bell’s palsy?

Answer 9

because facial nerve innervates stapedius muscle (attaches to stapes ossicle and functions along with tensor tympani to dampening incoming sound.)

Question 10

which two muscles in the middle ear are involved in dampening incoming loud sounds? what are their associated Cranial nerves?

Answer 10

• tensor tympani (inserts on malleolus, attached to anterior wall of middle ear, innervated by CN V)
• stapedius muscles (inserts on stapes, attached to posterior wall of middle ear, innervated by CN VII)

-both these muscles constrict to pull on the ossicles to dampen the vibrations

Question 11

promontary?

Answer 11

large swelling on medial wall of middle ear, formed by basal turn of the cochlea

Question 12

some patients with middle ear infection may hear and feel throbbing , why might this be?

Answer 12

internal carotid artery runs in carotid canal through the middle ear. fluid/infection/swelling would put pressure on this canal.

Question 13

through which foramen does the facial nerve exit from the facial canal?

Answer 13

stylomastoid foramen

Question 14

location and structures of the inner ear?

Answer 14

imbedded in petrous part of temporal bone behind the oval window.
structures are found within the bony labyrinth (filled with perilymph).
membranous labyrinth is a continuous sac suspended in the bony labyrinth. sac is filled with endolymph.

Question 15

which part of bony labyrinth contains membranous labyrinth with sensory receptors for hearing

Answer 15

cochlea

Question 16

which part of bony labyrinth contains membranous labyrinth with sensory receptors for static equilibrium

Answer 16

vestibule

Question 17

utricle location and function (inner ear)?

Answer 17

inside bony vestibule, contains sensory receptors for static equilibrium (some dynamic equilibrium)

Question 18

3 orientations of semicircular ducts?

Answer 18

horizontal, anterior and posterior

Question 19

Ampulla location and function?

Answer 19

within bony vestibule, contains sensory receptors for Dynamic equilibrium

Question 20

where does the vestibulocochlear nerve (CN VIII) exit the inner ear?

Answer 20

internal acoustic meatus

Question 21

in which duct are sensory receptors for hearing located?

Answer 21

cochlear duct

Question 22

how are high pitched and low pitched sounds relayed from environment to the cochlear duct receptors?

Answer 22

sounds are collected as vibrations in the auricle, transmitted through the tympanic membrane to the ossicles, high pitched sounds cause high frequency vibrations of the ossicles (opposite for low pitch sounds)
–> through to oval window where high frequency sound receptors are at the base (proximal) of the cochlear duct and low pitch receptors are at the apex of the cochlear duct (distal).

Question 23

how does the vestibular system pick up on head movements?

Answer 23

as head moves in particular direction, relative movement of endolymph past sensory receptors in Ampulla causes activation of receptors in particular part of semicircular ducts (horizontal, anterior, posterior—depending on the direction)