Control L18 auditory pathways

Question 1

What parts of the skull are related to the ear’s location?

Answer 1

externally:
squamous part of temporal bone
external auditory meatus (canal)
mastoid process

internally:
squamous part of temporal bone
petrous part of temporal bone
internal auditory meatus (canal)

Question 2

What cranial nerves travel through the internal auditory meatus?

Answer 2

CN VII and VIII

Question 3

What is the function of the external ear?

Answer 3

auricle receives sound waves and funnels them to the external acoustic canal

Question 4

what is the function of the middle ear?

Answer 4

Transformation of sound waves into mechanical waves/vibrations

Question 5

what is the function of the inner ear?

Answer 5

conversion of mechanical waves into electrical waves/signals

Question 6

what is the anatomical name for the eardrum?

Answer 6

the tympanic membrane

Question 7

what is the middle ear?

Answer 7

an air filled space in the petrous part of the temporal bone. seperated from external ear by tympanic membrane

Question 8

what bones are found in the middle ear?

Answer 8

the ossicles - malleous, incus and stapes (closer to outer –> closer to inner ear)

Question 9

how does the middle ear communicate with the nasopharynx?

Answer 9

the pharyngotympanic tube aka eustachian tube

Question 10

why are middle ear infections more common in infants?

Answer 10

as the pharyngotympanic tube is positioned quite flat so infection spreads easier than in an adult who has a more angled pharyngotympanic tube where gravity prevents infection moving up into the ear easily

Question 11

what is the role of the pharyngotympanic tube?

Answer 11

equalise pressure between internal environment and atmospheric pressure

Question 12

why is the middle ear a high risk space for infections/spread of infection?

Answer 12

has close relationships with other surrounding structures:
- with nasopharnyx via pharnygotympanic tube
- with cranial cavity (specifically middle cranial fossa) via mastoid air cells
- with IJV which lies inferiorly so risk of thrombosis
- internal carotid artery which lies anteriorly and can lead to pulsatile tinitis
- facial muscles and tongue via facial nerve as middle ear is transversed by chorda tympani and facial canal.
- parotid gland via lesser petrosal nerve
- inner ear via the oval window

Question 13

what are the two special sense organs in the inner ear?

Answer 13

the vestibular system
cochlear system and cochlear ducts

Question 14

what is the role of the vestibular system?

Answer 14

maintain balance and equilibrium

Question 15

what is the vestibular system formed of?

Answer 15

vestibule
semicircular canal
semicicrular ducts

Question 16

what nerve supplies the vestibular system?

Answer 16

vestibular nerve

Question 17

how is the cochlear organised?

Answer 17

tonotopically - highest frequency sounds/pitch received at base and gets lower towards apex

Question 18

what nerve supplies the cochlear system?

Answer 18

cochlear nerve

Question 19

what nerve does the cochlear and vestibular nerve develop from?

Answer 19

CN VIII - vestibulocochlear

Question 20

what is the function of the cochlear system?

Answer 20

hearing

Question 21

what are the fluid filled cavities in the inner ear called?

Answer 21

membranous (inner) labyrinth filled with endolymph
bony (outer) labyrinth filled with perilymph

Question 22

where are the fluid filled cavities of the inner ear found?

Answer 22

within the petrouts part of the temporal bone

Question 23

How do sound waves –> mechanical waves –> electrical signal?

Answer 23

sound waves hit tympanic membrane causing ossicles to vibrate. The vibration of the stapes bone hits the oval window which causes fluid waves in the perilymph of the bony cochlear deforming the endolymph inside the cochlear duct of the inner ear. The cochlear duct contains the spiral organ which converts the waves into electrical signals.

Question 24

what separates the bony cochlear into two chambers?

Answer 24

cochlear ducts

Question 25

what are the two chambers of the bony cochlear?

Answer 25

scala vestibuli (superior) scala tympani (inferior)

Question 26

what is found inside the cochlear duct?

Answer 26

endolymph spiral organ (of corti)

Question 27

where do the two bony chambers become continuous?

Answer 27

at the apex of the cochlear via the helicotrema (a narrow slit)

Question 28

what is the spiral organ of corti? How does it convert fluid waves/pressure into an electrical signal?

Answer 28

a structure within the cochlear duct that sits above the basilar membrane and contains hair cells with tips embedded into the tectorial membrane. It moves with the fluid waves so can detect deformation of the endolymph in cochlear duct by the perilymph in the surrounding bony chambers. It converts fluid pressure into electrical signals via the cochlear nerve.

Question 29

in what cochlear cavity is the cochlear duct found?

Answer 29

in the membranous labyrinth

Question 30

what are properties of the auditory pathway?

Answer 30

polysynaptic tonotopically organised bilateral (so sound can be localised) compares input of timing and loudness of sound

Question 31

What is the pathway of signals from the inner ear to the auditory cortex?

Answer 31

1. primary neruons via the cochlear nerve (formed of axons of bipolar neurons in spiral ganglion) project to the dorsal and ventral cochlear nuclei in the rostral medulla. 2. Fibres synapse here and then travel via secondary neurons bilaterally to the superior olivary nuclei at the level of the mid pons. 3. superior olivary nucleus sends bilateral ascending fibres to the inferior colliculus as the lateral lemniscus 4. inferior colliculi receive fibres in the lateral lemniscus and exchanges info between right and left via the inferior colliculus commissure 5. auditory information sent to medial geniculate nucleus via the brachium of the inferior colliculus 6. information sent from MGN to primary auditory cortex via auditory/acoustic radiations

Question 32

where does CN VIII enter the brainstem?

Answer 32

at the cerebellopontine angle

Question 33

what is the trapezoid body?

Answer 33

the fibres of the secondary neurons of the auditory pathway which travel to the contralateral side

Question 34

what part of the brainstem are the inferior colliculi found?

Answer 34

dorsal surface in the tectum of midbrain

Question 35

what part of the brainstem is the medial geniculate nuclei found?

Answer 35

dorsal surface and are projections of the thalamus

Question 36

what connects the inferior colliculus to the medial geniculate nucleus>

Answer 36

brachium of inferior colliculus

Question 37

where is the primary auditory cortex found?

Answer 37

superior temporal gyrus aka Heschl's gyrus

Question 38

what pitch sounds are heard at which part of the cochlear?

Answer 38

apex = low pitch base = high pitch pitch increases from apex --> base

Question 39

how is pitch of sound distributed in the auditory cortex?

Answer 39

low frequency = antereolateral part high frequency = posteromedial part

Question 40

which hemisphere house the secondary auditory areas specialised for linguistic functions?

Answer 40

left

Question 41

what are the two secondary auditory areas specialised for linguistic functions

Answer 41

expressive speech area aka Broca's area receptive speech area aka Wernicke's area

Question 42

what is the role of Broca's area?

Answer 42

production and fluency of words

Question 43

what is the role of Wernicke's area?

Answer 43

understanding of words

Question 44

How is speech affected by Broca's aphasia?

Answer 44

It becomes non-fluent but understands the words

Question 45

How is speech affected by Wernicke's aphasia?

Answer 45

Speech is still fluent but lack of understanding of what they're saying/what they're saying doesn't make sense

Question 46

what artery supplies the associated auditory areas (Broca's and Wernicke's)?

Answer 46

MCA

Question 47

what are the two auditory reflexes?

Answer 47

protection from loud noises - via CN V3 and VIII contracting the tensor tympani muscle and stapedius muscle respectively preventing damage movement in response to sound - via CN III, IV and VI moving head and eyes

Question 48

what is the smallest bone in the body?

Answer 48

stapes

Question 49

where are the cell bodies of the hair cell axons?

Answer 49

in the spiral ganglion

Question 50

What is the difference between the inferior colliculi and the inferior colliculus commissure?

Answer 50

inferior colliculus = collection of cell bodies inferior colliculus commissure = bundle of axons which signal between the two inferior colliculi