Hearing Flashcards
what are the three division of the ear
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
how long is the ear canal before reaching the tympanic membrane
2-3cm
what is the role of the tympanic membrane
external auditory canal transmits sound waves towards the tympanic membrane
which aids transduction of sound to mechanical energy
what are the three ossicles of the middle ear
malleus
incus
stapes
what is the role of the ossicles and what happens with age
vibrate and amplify / transmit sound waves into the cochlea ear
calcify with time so can’t vibrate as much = hearing gloss
why is the middle ear a high risk space
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
what is the structure and role of the eustachian tube
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
what two systems make up the inner ear
vestibular (balance and equalibrium) and cochlear system (hearing)
combine to form cranial nerve 8
where is the inner ear located
in petrous part of the temporal bone
what is the difference in role o the tip vs base of the cochlea
tip = low frequency sound s base = higher frequency sounds
what is the difference between the bony outer labyrinth of the ear and the membranous inner labyrinth
in the inner ear
outer = perilymph (extra cellular fluid)
inner - endolymph (intracellular fluid)
what is the role of the cochlear duct
(bony labyrinth) separates cochlea into scala vestibuli (upper part) and scala tympani (lower part)
what structure allows the scala vestibuli/tympani to be continuous
at the apex via narrow slit called heliocotrema
describe the route of the vibrations in the inner ear
enter from the stapes into the scala vestibuli and pass through the cochlear to the scala tympani and reabsorbed at the round window
describe the structure of the cochlear duct and the organ of corti
superior to the basilar membrane
has hair cells with tips embedded in the tectorial membrane - hair cell axons travel to spiral ganglia
describe in general the mechanism of sound along the cochlear, SV and ST
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
how is the auditory pathway neuronally structured
polysynaptic, tonotopically organised, bilateral, compares timing and loudness
describe the route of the 1 auditory fibres
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
where to you find cochlear nuclei and where do they project
open medulla - receive afferent from the cochlear nerve
project bilaterally to superior olivary and into the lateral leminsucs
what is the role of the superior olivary nucleus (SON) and lateral leminscus in the auditory pathway
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
describe the tonotopic structure of the primary auditory cortex
heschels gyrus (temporal lobe)
low frequency sounds at the anterolateral part
high frequency at the posteriomedial part
where do you find the 2ndary auditory areas
left hemisphere
(posterior) wernickes - sensory, understanding of words
(anterior) broca - motor production fo words
what is damage to the 2ndary auditory areas commonly caused by
damage to the middle cerebral artery
what are two examples of descending auditory pathways
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
