Chapter 11 – The Auditory Nerve and Central Auditory Pathways

Vocabulary flashcards covering anatomical structures, physiological concepts, disorders, diagnostic criteria and management related to the auditory nerve and central auditory pathways.

Central Auditory System

Network of brainstem, midbrain and cortical structures that receive and analyze acoustic information from both ears.

Auditory Nerve (Cranial Nerve VIII)

Bundle of ~30,000 cochlear and ~20,000 vestibular fibers that transmit hearing and balance signals from the inner ear to the brainstem.

Internal Auditory Canal (IAC)

Bony canal running from the cochlear modiolus to the base of the brain that carries the vestibulocochlear nerve, facial nerve and internal auditory artery.

Intrinsic Redundancy

Multiple parallel neural pathways within the auditory system that repeatedly analyze acoustic messages, increasing resiliency of signal transmission.

Extrinsic Redundancy

Redundant cues built into speech (e.g., syntax, context) that aid comprehension even when parts of the signal are degraded.

Tonotopic Organization

Ordered arrangement of auditory nerve fibers: high-frequency (basal) fibers on the outer portion and low-frequency (apical) fibers on the inner portion of the bundle.

Cerebellopontine Angle (CPA)

Junction of cerebellum, medulla and pons where auditory and vestibular nerves separate; common site for acoustic neuromas.

Decussation

Crossover point where neural fibers cross to the opposite side of the brain.

Commissure

Bundle of nerve fibers that directly connects identical structures on the two sides of the brain.

Ipsilateral

Located on or affecting the same side of the body or brain.

Contralateral

Located on or affecting the opposite side of the body or brain.

Cochlear Nucleus

First brainstem nucleus receiving input from auditory nerve; divided into dorsal and ventral nuclei.

Trapezoid Body

Pons region marking the first major decussation of auditory fibers, initiating bilateral representation of monaural signals.

Superior Olivary Complex (SOC)

Brainstem center that compares timing and intensity cues from both ears to localize sound and mediates acoustic reflexes.

Lateral Lemniscus

Major fiber tract carrying auditory impulses from SOC to inferior colliculus; receives input from both sides.

Inferior Colliculus

Midbrain nucleus integrating bilateral auditory input before relaying it to the thalamus.

Medial Geniculate Body (MGB)

Thalamic relay station (ventral division for audition) that sends auditory information to the cortex.

Heschl’s Gyrus (Superior Temporal Gyrus)

Primary auditory cortex within temporal lobes where conscious perception of sound occurs.

Sensorineural Hearing Loss (SNHL)

Permanent loss arising from inner ear or neural pathway damage; auditory-nerve lesions manifest as SNHL.

Tinnitus

Perception of sound (ringing, buzzing) without external source; common early symptom of auditory-nerve disorders.

Acoustic Neuroma (Vestibular Schwannoma)

Benign tumor of Schwann cells, usually in the IAC, that can produce unilateral SNHL, tinnitus, dizziness and facial symptoms.

Acoustic Neuritis

Inflammation of the auditory nerve, often viral, leading to sudden SNHL and dizziness.

Multiple Sclerosis (MS)

Demyelinating disease that can disrupt auditory neural conduction and mimic auditory-nerve disorders.

Auditory Neuropathy Spectrum Disorder (ANSD)

Condition with normal outer-hair-cell function but dys-synchronous VIII-nerve firing, causing mild–moderate SNHL and poor speech recognition.

Auditory Brainstem Response (ABR) Latency Delays

Diagnostic clues: Wave I delay = peripheral lesion; Wave III delay = auditory nerve/lower brainstem lesion; Wave V delay = higher brainstem lesion.

Central Deafness

Rare bilateral cortical or subcortical lesion causing profound loss of auditory perception despite intact ears.

(Central) Auditory Processing

Efficiency and effectiveness with which the CNS uses auditory information for skills like localization, discrimination and temporal processing.

Central Auditory Processing Disorder (CAPD)

Deficit in neural processing of auditory stimuli not due to higher-order cognitive or language problems.

Sound Localization

Ability to identify a sound’s origin in space, largely mediated by SOC comparisons of binaural cues.

Auditory Discrimination

Skill of distinguishing subtle differences between speech sounds or non-speech stimuli.

Auditory Pattern Recognition

Identification of pitch, duration and intensity patterns in auditory sequences.

Temporal Aspects of Audition

Processing of timing cues such as gap detection and speech rhythm essential for speech understanding.

Auditory Figure-Ground

Skill of understanding speech in competing background noise.

Auditory Closure

Ability to fill in missing or degraded parts of speech to derive meaning.

Binaural Integration

Dichotic listening ability to combine different inputs presented simultaneously to each ear and report both.

Binaural Separation

Dichotic skill to focus on and repeat material from one ear while ignoring the other.

Temporal Processing

Detection and use of rapid timing cues (e.g., phoneme differences, prosody) in speech perception.

Executive Functions

Higher-order cognitive skills (attention, planning, inhibition, memory) that can overlap with auditory processing abilities.

Binaural Interaction Tests

Assessments such as Masking-Level Difference and Rapidly Alternating Speech Perception that evaluate integration of signals between ears.

Temporal Patterning Tests

Measures like Gaps-in-Noise and Auditory Duration Patterns that test temporal ordering and resolution.

Monaural Speech Tests

Central tests (e.g., Filtered Speech, Time-Compressed Speech) presenting degraded signals to one ear to stress higher pathways.

SCAN

Screening battery for Auditory Processing Disorders incorporating figure-ground, filtered words and competing words.

Comorbidity

Co-existence of CAPD with other disorders (e.g., ADHD, language impairment) due to overlapping neural networks.

CAPD Test Candidate Criteria

Age ≥7, normal peripheral hearing, native English, average IQ, and absence of severe language, cognitive or attention deficits.

CAPD Diagnosis Criteria

Deficits ≥2 SDs below mean on two+ tests or ≥3 SDs on one test with functional difficulty, after ruling out other disorders.

Management for APD

Environmental modifications, auditory training software, language/reading therapy, FM systems and multidisciplinary collaboration.