The Auditory Nerve and Central Auditory Pathway

Internal Auditory Canal

afferent neurons exit the cochlea through the modiolus forming the cochlea portion of the vestibulocochlear nerve

begins at the cochlear modiolus and ends at the base of the brain

passing through the IAC are the

vestibulocochlear nerve (CN8)

facial nerve (CN7)

internal auditory artery

auditory nerve fiber organization

fibers spiral together to form a bundle that is tonotopically organized

basal, high freq are on the outer portion

apical, low freq on the inner portion

cerebellopontine angle (CPA)

place on the brain-stem where the cerebellum, medulla oblongata, and pons join together

point within the brain-stem where the auditory and vestibular nerves separate

decussations

crossover points within the brain that unite symmetrical portions

commissures

nerve-fiber bundles that unite similar structures on both sides of the brain

ipsilateral

on the same side

constralateral

on the opposite side

cochlear nucleus

receives info from auditory nerve fibers as they enter the cerebelloponstine angles

two nuclei: dorsal cochlear nuclei, ventral cochlear nuclei

trapezoid body

located within pons

represents the start of bilateral representation of a signal presented to one ear

routes signal to the superior olivary complex, contralateral superior olivary complex, and lateral lemniscus

first decussation point of the auditory system

Superior Olivary Complex

receives input from the ipsilateral and contralateral cochlear nuclei

allows for sound localization by analyzing the temporal and intensity differences of a sound reaching both ears

Controls the reflex activity of the stapedisus and tensor tympani muscles

Routes signal to the inferior colliculus via the lateral lemniscus

Lateral Lemniscus

pathway for the transmission of impulses from the ipsilateral lower brainstem connecting the SOCs to the inferior colliculus

routes signal from the SOCs to the inferior colliculus

receives afferent stimulation from both SOCs

inferior colliculus

receives afferent stimulation from both SOCs

medial geniculate body (MGB)

located within the thalamus

last subcortical relay station for auditory impulses

ventral division of MGB is primarily responsible for auditory information

routes signal to auditory cortex

Heschl’s Gyrus

aka superior temporal gyrus

area of auditory reception located within the temporal lobes on both sides of the cerebral cortex

auditory system is considered a sensory system (gives brain info from the cochlea)