Ear Physiology and Anatomy

Question 1

what is in the outer ear?

Answer 1

the pinna

the external auditory canal

Question 2

what is in the middle ear?

Answer 2

tympanic membrane 
semicircular canal 
malleus 
incus 
long process of incus 
stapes footplate 
stapes crus

Question 3

what is in the inner ear?

Answer 3

cochlea
cochlea nerve
vestibular nerve
eustachian tube

Question 4

describe the external auditory canal?

Answer 4

skin-lined tube
2.5cm long leading down to the tympanic membrane
outer 3rd is cartilaginous and contains hair and sebaceous and ceruminous glands
inner 2/3rds walls are bony

Question 5

how should the outer ear be cleaned?

Answer 5

self-cleaning
skin is migratory so there are no indications to use cotton wool buds
wax should only be seen in the outer 3rd

Question 6

describe the middle ear?

Answer 6

an air-containing derived from the branchial clefts
communicates with the mastoid air cells superiorly
Eustachian tube connects it to the nasopharynx medially

Question 7

what is the role of the Eustachian tube?

Answer 7

ventilates the middle ear
maintains equal air pressure across the tympanic membrane
it is normally closed but opens via the action of palatal muscles to allow air entry when swallowing or yawning

Question 8

what happens when there is a defect in the eustachian tube mechanism e.g. in cleft palate?

Answer 8

prevents air entering the middle ear cleft which may fill with fluis

Question 9

what are the 3 ossicles?

Answer 9

malleus, incus, stapes

they lie in the middle ear cavity and transmit sound from the tympanic membrane to the inner ear

Question 10

what nerve is in the middle ear cavity?

Answer 10

the horizontal segment of the facial nerve is on the medial wall of the cavity
potential to be damaged during surgery or by direct extension of infection in the middle ear

Question 11

what are the structure of the inner ear for hearing?

Answer 11

vestibule

Question 12

what is the structure of the inner ear for balance?

Answer 12

semicircular canals

there is a semicircular canal arranged in each body plane and these are stimulated by rotatory movement

Question 13

what is the nerve passage through the inner ear?

Answer 13

facial, cochlear and vestibular nerves emerge from the inner ear and run through the internal acoustic meatus to the brainstem

Question 14

how do we hear?

Answer 14

1. ossicles in the middle ear transmit sound waves from the TM to the cochlea
2. this amplifies the waves by roughly 18-fold to compensate for the loss of sound waves moving from the air-filled middle ear to the fluid-filled cochlea
3. Hair cells in the basilar membrane of the cochlea detect the vibrations and transduce there into nerve impulses
4. they then pass to the cochlear nucleus and eventually to the superior olivary nuclei of both sides

Question 15

affects of lesions central to the cochlear nucleus

Answer 15

don’t cause unilateral hearing loss

Question 16

how can sound reach the cochlea if the ossicles are diseased?

Answer 16

by vibration of the temporal bone (bone conduction)