Exam 3 final
1. Gross anatomy structures of the VIII CN & Auditory Pathway (CANS)
What forms the auditory portion of the VIII nerve?
The spiral ganglion forms the auditory portion of the 8th cranial nerve.
Describe the main pathway from the ear to the brain.
Spiral ganglion →
VIII cranial nerve →
Cochlear nucleus →
Superior olivary complex (localization: timing & intensity cues) →
Lateral lemniscus (tract) →
Inferior colliculus (binaural processing & localization) →
Medial geniculate body →
Primary & secondary auditory cortex
Does information travel up one side or both?
Both sides, but the strongest pathways cross to the opposite side.
What is decussation?
It means crossing to the opposite side of the brain.
Explain the Right Ear Advantage (REA).
The right ear sends its strongest signals to the left hemisphere, where speech is processed
Left ear input must cross the corpus callosum to reach the left hemisphere → weaker.
2. Types of Hearing Loss (Inner Ear vs CANS)
Sensorineural vs Retrocochlear: How do they look on the audiogram?
Exactly the same.
Can you tell the difference between them on an audiogram?
No.
What does “sensori” refer to?
The cochlea / inner ear (hair cells).
What does “neural” refer to?
The VIII nerve or beyond (neural firing & timing).
Red flags for retrocochlear pathology:
Asymmetric hearing
Unilateral tinnitus
Vertigo
Poor word recognition (especially one ear)
3. Key Terms
Decussate
To cross from one side of the brain to the other.
Ablation
Removal or destruction of tissue.
Commissurotomy
A surgical cut of a commissure (the connection between hemispheres).
Ipsilateral vs Contralateral
Ipsilateral: same side
Contralateral: opposite side
Retrocochlear nystagmus
Abnormal, rhythmic eye movement associated with lesions beyond the cochlea.
VII Cranial Nerve (Facial Nerve)
Controls facial muscles. Damage can cause Bell’s Palsy.
How can facial nerve damage occur?
Middle ear damage or skull fractures.
4. Auditory Neuropathy Spectrum Disorder (ANSD)
What is it?
Inner ear detects sound normally, but the VIII nerve fires out of sync.
Causes?
Defective inner hair cells
Desynchronized neural firing along VIII nerve
Hearing thresholds?
Can be:
normal
mildly impaired
severely impaired
→ Highly variable
Speech perception?
Always poor.
Speech & language delays are common.
5. Central Auditory Processing Disorder (CAPD)
Peripheral system?
Normal — the problem is beyond the VIII nerve.
What do these people look like?
“I can hear but I can’t understand.”
Difficulty following directions
Trouble hearing in noise
Mishearing words
Slow processing of auditory information
Three categories of CAPD causes:
Neurological factors
Tumors
Lesions
Ablations
Seizure disorders
Maturational factors
Developmental lag in CANS
Abnormal hemispheric representation/transfer
Neuromorphological factors
Polymicrogyria (underdeveloped gyri)
Heterotopia/ectopic brain areas
Three categories of treatment:
Environmental modifications (FM system, seating)
Remediation/therapy
Compensatory strategies (note-taking supports, chunking)
6. Vestibular System – Gross Anatomy
Semicircular Canals (SCCs)
Lateral
Anterior
Posterior
Detect angular head movement.
Bony labyrinth
Filled with perilymph.
Membranous labyrinth
Filled with endolymph.
Hair cells (cilia)
Convert movement into neural signals.
Utricle
Horizontal orientation
Detects horizontal linear acceleration & horizontal head tilts
Saccule
Vertical orientation
Detects vertical linear acceleration (up/down movements)
Ampullary cupula
Bulging base of semicircular canals.
Crista / Otoconia
"ear rocks" — when displaced, cause BPPV.
Vestibular nerve
Part of the VIII CN.
7. Vestibular Terms & Disorders
Vertigo vs Dizziness vs Unsteadiness
Vertigo: spinning sensation
Dizziness: vague lightheadedness
Unsteadiness: imbalance while walking/standing
Vestibulotoxins (know examples):
Meclizine
Diazepam
Promethazine
Chlorthalidone
Furosemide
Hydrochlorothiazide
Gentamicin (big one!)
Dexamethasone
BPPV
Otoconia in SCCs
Brief vertigo with head movement
Acoustic Neuroma / Vestibular Schwannoma
Compresses hearing & balance portions of VIII nerve
Causes unilateral symptoms
AIED (Autoimmune Inner Ear Disease)
Immune system attacks inner ear, causing fluctuating or sudden HL.
PPPD
Persistent, chronic dizziness without true vertigo.
Meniere’s Disease
Progressive
Too much endolymph
Fluctuating SNHL
Episodic vertigo
Aural fullness & tinnitus
Treated depending on stage
Mal de Débarquement
Rocking sensation after cruise/long flight.
Age-related vestibular problems
Due to degeneration of vestibular hair cells, pathways, or CNS.
8. Syndromes Associated With Hearing Loss
Apert Syndrome
CHARGE Syndrome
Towns-Brocks Syndrome
Treacher Collins Syndrome
Connexin 26 mutation (nonsyndromic HL)
⭐ 1. FULL PATHWAY – From Cochlea → Cortex
Know the order in your sleep:
VIII CN (auditory portion / spiral ganglion fibers)
Cochlear nucleus
Superior olivary complex
localization (timing + intensity cues)
Lateral lemniscus
Inferior colliculus
Medial geniculate body
Primary auditory cortex (Heschl’s gyrus)
Secondary auditory cortex
Also know:
What decussation means
Why the right ear advantage (REA) exists
Why ipsilateral pathways are weaker but still important
⭐ 2. All Retrocochlear Red Flags
You MUST know all of these:
Asymmetry on audiogram
Unilateral tinnitus
Vertigo/dizziness
Poor word recognition especially one ear
Abnormal reflexes
Facial weakness (if VII involved)
Nystagmus
⭐ 3. Major Disorders
You need features, symptoms, and how they behave.
Vestibular Schwannoma
Grows on VIII CN
Often affects balance first, then hearing
Progressive unilateral SNHL
Poor WRS
Unilateral tinnitus
Auditory Neuropathy Spectrum Disorder
OHC function normal
IHC + nerve firing desynchronized
Absent/abnormal ABR
Speech perception VERY poor
CAPD
Know:
Characteristics
Normal peripheral hearing
Trouble with processing
Causes (neurological, maturational, neuromorphological)
Management (environmental, remediation, compensatory)
⭐ 4. Vestibular System – ALL TERMS
You must know:
Structure & Function
SCCs — rotational movement
Utricle — horizontal linear movement
Saccule — vertical linear movement
Ampulla & cupula
Otoconia (ear rocks)
Endolymph vs perilymph
Vestibular nerve pathways
Vertigo vs Dizziness vs Unsteadiness
Be able to define these EXACTLY.
Common Disorders
BPPV
otoconia in SCC
brief vertigo w/ head movements
Meniere’s
too much endolymph
fluctuating HL
roaring tinnitus
episodic vertigo
aural fullness
PPPD
Age-related vestibular decline
Motion-triggered disorders (like mal de barquement)
Vestibulotoxins
Know: Meclizine, Diazepam, Gentamicin, Dexamethasone, diuretics.
⭐ 5. Syndromes Affecting Hearing
You DON’T need genetics, just the basics:
Apert’s Syndrome
CHARGE
Towns-Brocks
Treacher Collins
Connexin 26 (non-syndromic, genetic SNHL)
⭐ 6. Vocabulary You Must Know
These ALWAYS show up as test questions:
Decussation
Ipsilateral vs contralateral
Commissurotomy
Ablation
Retrocochlear
Sensorineural vs neural vs “sensory”
Otoconia
Endolymph vs perilymph
Cupula
Nystagmus
⭐ 7. What You CANNOT Tell From an Audiogram
You CANNOT tell SNHL vs retrocochlear based only on thresholds.
You need speech scores + symptoms.
This is 100% testable.
⭐ 8. Right Ear Advantage (REA)
You need to know:
Why right ear → left hemisphere faster
Left ear must cross corpus callosum
REA strongest in speech / dichotic listening tests
⭐ 9. Bonus — Things Teachers Often Test
Even if not highlighted:
Why bilateral pathways are important
Why damage ABOVE the cochlea → processing disorder
Differences between peripheral and central issues
Which vestibular disorders are episodic vs constant