Hearing

Question 1

what are the three division of the ear

Answer 1

external - auricle, funnels sound waves into the canal - l lateral 1/3 cartilage, medial 2/3 is bony

middle ear - sound waves - mechanical waves via ossicles

inner ear mechanical waves to electrical impulses

Question 2

how long is the ear canal before reaching the tympanic membrane

Answer 2

2-3cm

Question 3

what is the role of the tympanic membrane

Answer 3

external auditory canal transmits sound waves towards the tympanic membrane
which aids transduction of sound to mechanical energy

Question 4

what are the three ossicles of the middle ear

Answer 4

malleus
incus
stapes

Question 5

what is the role of the ossicles and what happens with age

Answer 5

vibrate and amplify / transmit sound waves into the cochlea ear
calcify with time so can’t vibrate as much = hearing gloss

Question 6

why is the middle ear a high risk space

Answer 6

connected to nasopharyngx and mastoid air cells which are prone to infection
thrombosis risk from internal jugular vein lying inferior
pulsatile tintitis from anterior carotid artery

Question 7

what is the structure and role of the eustachian tube

Answer 7

drinks, ventilates and equalises pressure in the ear
tubes need to be open to equalise
they are narrower in children to more likely to have infection

Question 8

what two systems make up the inner ear

Answer 8

vestibular (balance and equalibrium) and cochlear system (hearing)
combine to form cranial nerve 8

Question 9

where is the inner ear located

Answer 9

in petrous part of the temporal bone

Question 10

what is the difference in role o the tip vs base of the cochlea

Answer 10

tip = low frequency sound s
base = higher frequency sounds

Question 11

what is the difference between the bony outer labyrinth of the ear and the membranous inner labyrinth

Answer 11

in the inner ear
outer = perilymph (extra cellular fluid)
inner - endolymph (intracellular fluid)

Question 12

what is the role of the cochlear duct

Answer 12

(bony labyrinth) separates cochlea into scala vestibuli (upper part) and scala tympani (lower part)

Question 13

what structure allows the scala vestibuli/tympani to be continuous

Answer 13

at the apex via narrow slit called heliocotrema

Question 14

describe the route of the vibrations in the inner ear

Answer 14

enter from the stapes into the scala vestibuli and pass through the cochlear to the scala tympani and reabsorbed at the round window

Question 15

describe the structure of the cochlear duct and the organ of corti

Answer 15

superior to the basilar membrane

has hair cells with tips embedded in the tectorial membrane - hair cell axons travel to spiral ganglia

Question 16

describe in general the mechanism of sound along the cochlear, SV and ST

Answer 16

sound travels through these structures displacing perilymph which displaces endolymph in the cochlear duct which causes hair cells to press against the tectorial membrane opening the ion channels in the cells causing depolarisation

Question 17

how is the auditory pathway neuronally structured

Answer 17

polysynaptic, tonotopically organised, bilateral, compares timing and loudness

Question 18

describe the route of the 1 auditory fibres

Answer 18

axons of bipolar neon in spiral ganglion from the cochlear division of the CN8 enters the brainstem at the cerebellopontine angle (rostral medulla)
synapse with 2 neurones in dorsal and ventral cochlear nuclei

Question 19

where to you find cochlear nuclei and where do they project

Answer 19

open medulla - receive afferent from the cochlear nerve

project bilaterally to superior olivary and into the lateral leminsucs

Question 20

what is the role of the superior olivary nucleus (SON) and lateral leminscus in the auditory pathway

Answer 20

Son receives bilateral auditory info
sends ascending fibres to inferior colliculus via lateral leminsucs

info is then sent to the medial geniculate nucleus (MGN) of the thalamus via the acoustic radiation

Question 21

describe the tonotopic structure of the primary auditory cortex

Answer 21

heschels gyrus (temporal lobe)
low frequency sounds at the anterolateral part
high frequency at the posteriomedial part

Question 22

where do you find the 2ndary auditory areas

Answer 22

left hemisphere

(posterior) wernickes - sensory, understanding of words
(anterior) broca - motor production fo words

Question 23

what is damage to the 2ndary auditory areas commonly caused by

Answer 23

damage to the middle cerebral artery

Question 24

what are two examples of descending auditory pathways

Answer 24

from inferior colliculus to CN3,4,6 for head and eye movements

from superior olivary nucleus to stapedius via CN7 and tensor tympani via CNV3 - prevents damage during loud noise