auditory pathway Flashcards
where does the info in the auditory pathway travel from and to?
from receptors in organ of Corti of inner ear (cochlear hair cells) to CNS by vestibulocochlear nerve
where does the pathway ultimately reach?
primary auditory cortex for conscious perception
what are the 2 main components of the auditory pathway?
- primary (lemniscal) pathway
- non-lemniscal pathway
what is the primary pathway?
main pathway through which auditory information reaches the primary auditory cortex (A1)
what is the non-lemniscal pathway?
mediating unconscious perception such as attention, emotional response and auditory reflexes
what is the spiral ganglion?
- 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
when does the vestibular nerve join the cochlear nerve?
entering the internal acoustic meastus
from this point they are collectively knows as vestibulocochlear nerve
describe the passage of the nerve as it enters the cranium
enters cranium through IAM and travels a short distance to enter brainstem at cerebellopontine angle
what happens to the fibres from the cochlear nerve?
nerve bifurcates and info is sent to cochlear nuclei on each side of brainstem:
- ventral (ant) cochlear nucleus
- dorsal (post) cochlear nucleus
where is the ventral cochlear nucleus?
located in area where the nerve enters the brainstem
where is the dorsal cochlear nucleus?
located posterior to inferior cerebellar peduncle
forms a small bulge on surface of brainstem = auditory tubercle
from the dorsal cochlear nucleus, where do the fibres go?
most fibres cross the midline and ascend in contralateral lateral lemniscus
other fibres ascend in ipsilateral lateral lemniscus
from the ventral cochlear nucleus, where do the fibres go?
- some fibres also ascend in lateral lemniscus bilaterally
- but most fibres decussate to contralteral superior olivary nuclei
what part of the anatomy means that information from both ears travels bilaterally in each lateral lemniscus?
- in both dorsal and ventral nuceli some fibres decussate while others don’t
why is this important?
supranuclear lesions (above level of cochlear nucleus) will not lead to serious hearing impairment hearing problems can be conductive or sensorineural but not central
fibres ascend through lateral lemniscus from both cochlear nuclei. from the superior olivary nuceli, where do the fibres arrive?
arrive at the inferior colliculus, where all the fibres carrying auditory info converge
where do these fibres then project to?
ipsilateral medial geniculate body (MGB) in thalamus
what is the function of the MGB?
- relay centre
- has reciprocal connections with auditory cortex
- mediates refinement of incoming info
- projections from MGB proceed then to primary auditory cortex
where is the primary auditory cortex located?
located in superior temproal gyrus
right under lateral fissure
what are the non-lemniscal pathways?
pathways that do not lead to primary auditory cortex
involve multisensory integration, reflexes, attention and emotional responses
