auditory pathway

Question 1

where does the info in the auditory pathway travel from and to?

Answer 1

from receptors in organ of Corti of inner ear (cochlear hair cells) to CNS by vestibulocochlear nerve

Question 2

where does the pathway ultimately reach?

Answer 2

primary auditory cortex for conscious perception

Question 3

what are the 2 main components of the auditory pathway?

Answer 3

• primary (lemniscal) pathway

- non-lemniscal pathway

Question 4

what is the primary pathway?

Answer 4

main pathway through which auditory information reaches the primary auditory cortex (A1)

Question 5

what is the non-lemniscal pathway?

Answer 5

mediating unconscious perception such as attention, emotional response and auditory reflexes

Question 6

what is the spiral ganglion?

Answer 6

• houses cell bodies of 1st order neurones
• these receieve info from hair cells in Organ of Corti
• travel within osseous spiral lamina
• their central axons form main component of cochlear nerve

Question 7

when does the vestibular nerve join the cochlear nerve?

Answer 7

entering the internal acoustic meastus

from this point they are collectively knows as vestibulocochlear nerve

Question 8

describe the passage of the nerve as it enters the cranium

Answer 8

enters cranium through IAM and travels a short distance to enter brainstem at cerebellopontine angle

Question 9

what happens to the fibres from the cochlear nerve?

Answer 9

nerve bifurcates and info is sent to cochlear nuclei on each side of brainstem:

• ventral (ant) cochlear nucleus
• dorsal (post) cochlear nucleus

Question 10

where is the ventral cochlear nucleus?

Answer 10

located in area where the nerve enters the brainstem

Question 11

where is the dorsal cochlear nucleus?

Answer 11

located posterior to inferior cerebellar peduncle

forms a small bulge on surface of brainstem = auditory tubercle

Question 12

from the dorsal cochlear nucleus, where do the fibres go?

Answer 12

most fibres cross the midline and ascend in contralateral lateral lemniscus
other fibres ascend in ipsilateral lateral lemniscus

Question 13

from the ventral cochlear nucleus, where do the fibres go?

Answer 13

• some fibres also ascend in lateral lemniscus bilaterally

- but most fibres decussate to contralteral superior olivary nuclei

Question 14

what part of the anatomy means that information from both ears travels bilaterally in each lateral lemniscus?

Answer 14

• in both dorsal and ventral nuceli some fibres decussate while others don’t

Question 15

why is this important?

Answer 15

supranuclear lesions (above level of cochlear nucleus) will not lead to serious hearing impairment
hearing problems can be conductive or sensorineural but not central

Question 16

fibres ascend through lateral lemniscus from both cochlear nuclei. from the superior olivary nuceli, where do the fibres arrive?

Answer 16

arrive at the inferior colliculus, where all the fibres carrying auditory info converge

Question 17

where do these fibres then project to?

Answer 17

ipsilateral medial geniculate body (MGB) in thalamus

Question 18

what is the function of the MGB?

Answer 18

• relay centre
• has reciprocal connections with auditory cortex
• mediates refinement of incoming info
• projections from MGB proceed then to primary auditory cortex

Question 19

where is the primary auditory cortex located?

Answer 19

located in superior temproal gyrus

right under lateral fissure

Question 20

what are the non-lemniscal pathways?

Answer 20

pathways that do not lead to primary auditory cortex

involve multisensory integration, reflexes, attention and emotional responses