NS 8: Special sense of hearing and ANS

Question 1

Lobe of cerebral cortex associated with hearing?

Answer 1

temporal

Question 2

common causes of conductive deafness?

Answer 2

otitis externa
otitis media
otosclerosis
excess cerumen in external ear
glue ear- chronic otitis media with effusion
ruptured tympanic membrane

Question 3

What component of the ear may be damaged with ageing, causing sensorineural deafness?

Answer 3

hair cells= vibration sensitive cells found in the Organ of Corti

Question 4

when are tuning fork tests reliable?

Answer 4

when a single type of hearing loss in 1 ear only

Question 5

what are the 2 sound parameters detected by the cochlea?

Answer 5

frequency and volume

Question 6

different functions of inner and outer hair cells in organ of corti?

Answer 6

inner= 1 row which detect sound
outer= 3 rows which amplify sound

Question 7

causes of sensorineural hearing loss?

Answer 7

sensory: hair cell destruction e.g. noise related
hair cell death e.g. with aminoglycoside drugs
neural: -Spiral ganglion damage (e.g. acoustic neuroma)
– Age-related hearing loss (ARHL, possible links with dementia?)
– Tinnitus - ‘phantom’ sound (associated with hearing loss)
– Auditory Neuropathy (ass. with hyperbilirubinaemia, neonatal Jaundice)
– Monaural deafness - destroys ability to localise a sound.

Question 8

examples of 4 treatments for hearing loss?

Answer 8

hearing aid
cochlear implant
hair cell regeneration
cochlea nucleus implants

Question 9

what structure does the organ of corti lie on?

Answer 9

the basilar membrane= width of which increases with distance from stapedial end, (from base to apex) and coupled to decrease in stiffness, this means high frequency sounds maximally displace membrane at stapedial end and low-frequency sounds maximally activate apical end.
=tonotopic localisation.

Question 10

which cells provide most of the signal in the vestibulocochlear nerve?

Answer 10

inner hair cells- receive little input from brainstem in contrast to outer hair cells- receive input from superior olivary complex which modifies the shape and response properties of these cells. Some also make direct contact with tectorial membrane which inner hair cells don’t, which may be important in modifying inner hair cells response to sound.
inner and outer hair cells change shape along scala media, modifying their tuning characteristics.

Question 11

test used to measure mobility of tympanic membrane?

Answer 11

tympanometry

Question 12

anatomical layers and neural innervation of tympanic membrane?

Answer 12

outer layer= skin= stratified squamous keratinized epithelium
middle layer= fibrous CT
inner layer= low columnar respiratory epithelium

neural innervation: outer part= auriculotemporal nerve from mandibular division of trigeminal, and small branch of vagus (auricular branch)
inner part= glossopharyngeal nerve * so infections of oropharynx may produce earache as same neural supply- referred pain.

Question 13

MAIN function of auditory ossicles?

Answer 13

impedence matching: without them, most of sound energy would be reflected as it hits the high impedence cochlear fluid, so sound would be lost.
also amplify force of tympanic membrane, and so sound is amplified and concentrated to oval window.

Question 14

joints between ossicles?

Answer 14

synovial joints

Question 15

functions of tensor tympani and stapedius?

Answer 15

prevent excessive vibrations of ossicles so offer protection to ear from large noises.

Question 16

surfaces of middle ear?

Answer 16

anterior wall= carotid wall-ICA
posterior wall= mastoid wall- mastoid air cells
medial wall= outer plate of oval window
lateral wall= inner plate of tympanic membrane= low resp. columnar epithelium
roof= tegmen tympanum
floor= jugular wall- IJV runs underneath

Question 17

4 functions of eustachian tube?

Answer 17

ventilation of middle ear
equilibration of air pressure between middle ear and atmosphere
drainage of mucous secretions from middle ear into nasopharynx
prevent infections of middle ear from upper respiratory tract by lymphoid tissue (adenoids) close to opening of Eustachian tube into nasopharynx.

Question 18

consequences of compromising Eustachian tube function?

Answer 18

PAIN as pressure build up as can’t equlibrate pressures between middle ear and atmosphere
Infection risk and may compromise hearing ability as can’t drain secretions from middle ear

Question 19

embryological origin of eustachian tube?

Answer 19

1st pharyngeal pouch (endoderm)

Question 20

innervation of nasopharynx?

Answer 20

maxillary division of trigeminal nerve

Question 21

how do central auditory paths differ from other sensory systems?

Answer 21

have bilateral representation of sounds i.e. input from both ears reaches the auditory cortex in the temporal lobe in both cerebral hemispheres.

Question 22

other than conduction by the auditory ossicles, how else can sound be conducted to the inner ear?

Answer 22

through the temporal bone- but this is much less efficient than going via the auditory ossicles. However, if conductive hearing loss, sound will travel better by BC, giving a rinne -ve test.

Question 23

how does stapedius reduce sound intensity, protecting the inner ear from large noises?

Answer 23

pulls stapes away from opening into internal ear

Question 24

3 fluid filled spaces in cochlea?

Answer 24

scala vestibuli
scala tympani= these 2 are part of bony labyrinth, contain perilymph.
cochlear duct= part of membranous labyrinth, contains endolymph.

vestibular membrane separates scala vestibuli and cochlear duct
basilar membrane separates scala tympani and cochlear duct

Question 25

what does the oval window open into?

Answer 25

the scala vestibuli

the round window opens into the scale tympani

Question 26

how are the auditory receptors along the basilar membrane stimulated?

Answer 26

inward and outward movements of stapes produces perilymphatic pressure waves between scala vestibuli and scala tympani, setting the cochlear duct into motion, which as it rests on the basilar membrane, also sets this into motion. Movement of basilar membrane stimulates auditory receptors, and mechanically amplifies sound. The oscillations are in a sequential manner, with higher frequencies (higher tone sounds) detected more proximally.

Question 27

how do membrane potentials of hair cells change with movement of the basilar membrane?

Answer 27

stereocilia project from hair cells, and tips of the longest stereocilia are in contact or embedded in overlying tectorial membrane, so when basilar membrane moved with fluid movmement in scale tympani, stereocilia bend, and this changes Ems of hair cells.

Question 28

which cells play the major role in discriminating sounds of different frequencies?

Answer 28

inner hair cells as each has a 1:1 synaptic relationship with as many as 20 spiral ganglion cells which innervate the inner hair cells.

Question 29

how does hair cell depolarisation take place?

Answer 29

stereocilia on hair cells bent following movement of the basilar membrane.
bending stereocilia open ionic channels in the apical membrane of the cilia, causing K+ influx from endolymph in the scale media. The depolarisation opens VOCCs in base of hair cells, and Ca2+ influx triggers neurotransmitter release. This activates afferent nerve endings of of spiral ganglion neurones, allowing AP propagation into CNS.

Question 30

where does neural coding of frequency and loudness of sound occur primarily?

Answer 30

in inner hair cells which have multiple synaptic connections with spiral ganglion afferents.

Question 31

how can an acoustic neuroma be responsible for facial drooping?

Answer 31

this is a tumour which almost always arises from part of vestibular nerve in the IAM.
Tumour spreads after initial growth, causing progressive sensori-neural deafness with cochlear nerve involvement, disequilibrium with vestibular nerve and facial wkness due to involvement of facial nerve which travels through IAM to enter the facial canal in the middle ear.

Question 32

what is presbycusis?

Answer 32

age related hearing loss

Question 33

define the auditory pathway

Answer 33

1st order neurones in spiral ganglion, and their dendrites synapse on hair cells of spiral organ of Corti.
central processes of these form cochlear nerve which enters IAM to travel to brainstem.
cochlear nerve terminates on 2nd order neurones in cochlear nuclei in brainstem.
all decussate after forming 3 acoustic striae and travel to midbrain, where synapse.
fibres then termiante in medial geniculate nucleus in thalamus. Auditory radiation then travels to primary auditory complex.

accessory nuclei in path= superior olivary nucleus, nuclei of trapezoid body and nuclei of lateral lemniscus.

Question 34

what do unilateral lesions in spiral organ, cochlear nerve or cochlear nuclei cause?

Answer 34

ipsilateral deafness

distal to cochlear nuclei results in virtually no loss of hearing as bilateralism of auditory impulses as they ascend in the brainstem.

Question 35

how does a cochlea implant help with sensory-neural hearing loss?

Answer 35

can stimulate spiral ganglion cells even if hair cells lost