Chapter 11: The Auditory Nerve & Central Auditory Pathways Flashcards
Internal Auditory Canal (IAC)
-Begins at the cochlear modiolus and ends at the base of the brain
What passes through the IAC?
-Vestibulocochlear nerve
-Facial nerve
-Internal auditroy artery
Auditory Nerve Fiber Organization
-Basal, high frequencies are on the outer portion
-Apical, low frequencies are on the inner portion
Cerebellopontine Angle (CPA)
-Place on brain stem where the cerebellum, medulla, and pons join together
-Point 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
-Same side
Contralateral
-Opposite side
Cochlear Nucleus
-Receives information from the auditory nerve fibers as they enter the CPA
Trapezoid Body
-Located in the pons
-Represents the start of the bilateral representation of a signal presented to one ear
-Routes signal to superior olivary complex, contralateral superior olivary complex, and lateral lemniscus
First decussation point of the auditory system
trapezoid body
Superior Olivary Complex (SOC)
-Receives input from cochlear nuclei
-Allows for sound localization
-Controls reflex activity of stapedius and tensor tympani
-Routes signal to inferior colliculus through the lateral lemniscus
Lateral Lemniscus
-Routes signal from the SOCs to the inferior colliculus
-Receives afferent stimulation from both SOCs
Medial Geniculate Body (MGB)
-Located in thalamus
-Last subcortical relay station for auditory impulses
-Ventral part is responsible for auditory information
-Routes signal to auditory cortex
Heschl’s Gyrus (Superior Temporal Gyrus)
-Area of auditory reception located within the temporal lobes on both sides of the cerebral cortex
Disorders of the Auditory Nerve Symtomology
-Tinnitus
-High freq SNHL
-Asymmetrical SNHL
-Speech recognition scores that are worse than expected given threshold levels
Acoustic Neuromas
-Benign tumors that originate in the internal auditory canal
-The larger the tumor grows, the more likely it is to cause damage as it presses against other nerves and the brain
Vestibular Schwannoma
-Another name for an acoustic neuroma as most acoustic neuromas begin in the Schwann cells on the sheath of the vestibular nerve
Audiologic Manifestations of Acoustic Neuromas
-unilateral growths
-tinnitus, dizziness, speech recognition difficulties
-progressive unilateral hearing loss
Auditory Neuropathy Spectrum Disorder (ANSD)
-Normal outer hair cell function with dyssynchronous firing of the auditory nerve
ANSD Audiologic Manifestations
-mild to moderate SNHL
-speech recognition scores disproportionately worse than the degree of measured loss
-doesn’t benefit much from amplification
Auditory Processing Disorder (APD)
-Individuals with APD present with difficulty interpreting auditory information without an accompanying hearing loss
-May complain of decreased hearing sensitivity but testing reveals hearing within normal limits
-Acquired (stroke, tumor, ms, head trauma) or congenital
Management of APD
-Collaboration of SLP and AUD
-AUD diagnoses and SLP implements therapy and conducts testing to reflect language ability and functional deficits of communication
