Lecture: The Auditory Pathway

Question 1

In which part of the temporal bone is the internal acoustic meatus located? give some characteristics

Answer 1

Petrous part
very, very hard
IAM - facial nerve, vestibulocochlear nerve

Question 2

What is the pharyngotympanic (Eustachian) tube?

Answer 2

Connects the middle ear to the nasopharynx

maintains equilibrium in pressure

Question 3

Why is the middle ear a high risk space for infection?

Answer 3

connected to:
the nasopharynx which is prone to infection
mastoid air cells - infection may spread to middle cranial fossa&raquo_space; encephalitis
Internal jugular vein lies inferior - thrombosis risk
Internal carotid artery - pulsatile tinnitus
Nerves - chorda tympani etc - infection risk

Question 4

What are the fluid filled cavities of the inner ear?

Answer 4

Vestibule
Semi-circular canals (posterior, anterior and lateral)
Cochlea

Question 5

What kind of fluid fills these cavities in the inner ear?

Answer 5

Perilymph

- high in sodium, low in postassium

Question 6

What kind of fluid is contained in the cochlear duct?

Answer 6

Endolymph

• more like intracellular fluid
• high potassium, low sodium

Question 7

What are the names of the chambers created by the cochlear duct?

Answer 7

Scala Vestibuli - above duct

Scala Tympani - below duct

Question 8

What is the name of the apex of the duct where these two chambers are continuous?

Answer 8

Helicotrema

Question 9

What is the entrance and exit to the cochlear called?

Answer 9

Entrance - Oval Window

Exit - Round Window

Question 10

Between which two membranes are the cochlear hair cells located?

Answer 10

Tectorial Membrane - superior

Basement Membrane - inferior

Question 11

Where does the vestibulocochlear nerve enter the brainstem?

Answer 11

Cerebellopontine angle

Question 12

At which level and via which structure does auditory information cross over the midline?

Answer 12

At the level of entry - cerebellopontine angle

Crosses over via Trapezoid Body

Question 13

Along what route does auditory information ascend to the primary auditory cortex?

Answer 13

Spiral Ganglion
Cochlear Nuclei
Superior Olivary Nucleus on other side (via trapezoid body)
Inferior Colliculus
Medial Geniculate Nucleus
Heschl's Gyrus

Question 14

Where is Heschl’s Gyrus located?

Answer 14

Superior temporal gyrus

extends deep into the cerebral hemispheres

Question 15

Give some specialisations of the auditory pathway

Answer 15

Polysynaptic

Bilateral - allows us to differentiate timing, loudness and therefore location

Question 16

Which regions of the basilar membrane respond to which types of sound?

Answer 16

Apex responds to Low pitch

sound information of low pitch projects to the anterolateral part of Heschl’s Gyrus

Question 17

What are the secondary auditory areas and what are their functions?

Answer 17

Broca’s area:
anterior
motor/production of words

Wernicke’s area:
posterior
sensory/understanding

Question 18

Describe the descending auditory pathways

Answer 18

typically motor pathways
travels back down the way they came up
send of branches to Tensor Tympani and Muscle of Stapedius

These dampen down loud noise, to prevent damage,
do so by tightening eardrum, holding stapes in place