12 Auditory pathway

Question 1

What is the structure of the cochlea?

Answer 1

Cochlea duct contains endolymph. Cochlea contains perilymph. Duct separates cochlea into scala vestibuli and scala tympani; which are continuous at the helicotrema.

Question 2

What is the route of 1o axons in the auditory pathway?

Answer 2

Bipolar neurones form cochlear nerve which joins vestibulocochlear nerve.
Enters brainstem at cerebellopontine angle. Synapses with 2o neurones in dorsal and ventral cochlear nuclei.

Question 3

What is the route of 2o axons in the auditory pathway?

Answer 3

From cochlear nuclei via the trapezoid body (bilaterally) to the superior olivary nucleus. Via lateral lemniscus to inferior colliculus (more crossing over). Via inferior brachium to medial geniculate nucleus. To Heschl’s gyrus.

Question 4

What is the tonotopic representation of Heschl’s gyrus?

Answer 4

Anterolateral : low pitch.

Question 5

What are the descending pathways involved in the auditory pathway?

Answer 5

Inferior colliculus: head and eye mvmt via CN III, IV, VI.
Superior olivary nucleus: stapaedius via CN VIII and tensor tympani via CN V3.
Cochlear nuclei: to cochlear.

Question 6

Differentiate between conductive and sensorineural hearing loss.

Answer 6

Conductive: defect until spiral ganglion.
Sensorineural: defect in spiral ganglion or cochlear nerve.

Question 7

Which ear will perceive Weber’s test as louder in conductive hearing loss and why?

Answer 7

Damaged ear.

Hearing in the normal ear is inhibited by ambient sound.

Question 8

Which ear will perceive Weber’s test as louder in sensorineural hearing loss and why?

Answer 8

Normal ear.

Sound needs to be amplified.