8TH CRANIAL NERVE ANATOMY & CLINICAL TESTING

1. VESTIBULOCOCHLEAR NERVE
- NITHIN
NAIR

2. INTRODUCTION
Stato-acoustic or Auditory nerve
8th cranial nerve
2 components: a) cochlear (hearing) b) vestibular (equilibrium)
OBJECTIVES
1) Anatomy and functions.
2) Purpose of test
3) How to test
4) Interpretations

3. ANATOMY AND FUNCTIONS
Cochlear Nerve:
Dorsal and ventral cochlear nuclei -- situated---
inferior cerebellar peduncle.
The auditory receptors -- hair cells of the organ of
corti
Innervated – peripheral processes of bipolar neurons
of spiral ganglion
Their central processes form cochlear nerve which
ends in dorsal and ventral cochlear nuclei

6. AUDITORY PATHWAY
The 1st sensory neuron lies in the spiral ganglion of
bipolar cell. The peripheral processes are distributed
to the organ of corti.The central processes form
cochlear nerve –ends in dorsal and ventral cochlear
nuclei.
The 2nd neuron fibres start from the dorsal and
ventral cochlear nuclei; their axons form trapezoid
body and ends in dorsal nucleus of trapezoid body of
the same and opp. side

7. AUDITORY PATHWAY
The 3rd neuron fibres from dorsal nuclei of trapezoid
body ascend as lat. Lemniscus on both sides. Some of
the fibres of lat. Lemniscus end in inf. Colliculus. Rest
of the lat. Lemniscus relays in med. Geniculate body.
The 4th neuron fibres from med. Geniculate body –
auditory radiations – pass thru sublentiform part of
internal capsule – projected to auditory cortex of
temporal lobe.

9. Vestibular Nerve:
The 4 vestibular nuclei are situated partly in medulla
and partly in pons in relation to the floor of 4th
ventrical.
Receptors – maculae of saccule and utricle (static
balance) and cristae of the ampullae of semicircular
ducts (kinetic balance)
Innervated – peripheral processes of bipolar neuron
of vestibular ganglion (acoustic meatus)
Their central processes –form vestibular nerve –
ends in vestibular nuclei.

11. Vestibular pathway:
Innervates the maculae of the urticle and succule
(sensitive to static changes in equilibrium)
The ampullae of semicircular canals(sensitive to
dynamic changes in equilibrium)
Impulses pass: vestibular nerve vestibular nuclei
(pontomedullary junction)
Fibres from vestibular nuclei pass via inferior
cerebellar peduncle cerebellum

12. Clinical symptoms:
Damage to cochlear nerve produces tinnitus and
sensorineural deafness.
Damage to vestibular nerve results in vertigo or
dizziness and nystagmus.
 Types of nystagmus:
1) Peripheral vestibular nystagmus
2) Central nervous system nystagmus
3) Optokinetic (railroad or freeway) nystagmus

13. Purpose of test:
To detect whether any deafness is bilateral or
unilateral, and whether sensorineural or
conduction.
To determine whether disturbance of
vestibular function originates in the labyrinth,
the vestibular nerve, or the brain stem.

14. HOWTO TEST

15. Method of testing:
A) For cochlear component
• 1) Rinne’stest
• 2) Weber’s test
• 3) Absolute bone conduction (ABC) test
• 4) Schwabach test
• 5) Audiometric test
• 6) Evoked response

16. B) For vestibular component
• 1) Rotationaltest.
• 2) Caloric test.
• 3) Dix Hallpikemaneuver for nystagmus.
• 4) Electronystagmography

17. Rinne’s test

18. Weber’s test

19. Audiometric test

20. Evoked response

21. Rotational test

22. Caloric test

23. Dix hallpike maneuver

24. Electronystagmography (ENG)

25. INTERPRETATIONS

26. Interpretations
Whether hearing loss is senorineural or conductive
TEST NORMAL CONDUCTIVE
DEAFNESS
SENSORINEURAL
DEAFNESS
Rinne AC > BC BC > AC AC > BC
Weber Not lateralized Lateralized to
diseased ear
Lateralized to
better ear
ABC Equal Lengthened Shortened
Schwabach Equal Lengthened Shortened

27. Interpretations
Whether nystagmus is peripheral or central
FINDING PERIPHERAL CENTRAL
LATENCY Yes 3 – 10 sec No
FATIGABILITY Yes No
NYSTAGMUS DIRECTION Fixed, typically mixed
rotational
Changing, variable and
pure vertical or pure
horizontal
SUPPRESSION BY VISUAL
FIXATION
Yes No
SEVERITY Markedly severe Mild to moderate
CONSISTENCY Less consistent More consistent
PAST POINTING In direction of slow
phase
In direction of fast
phase

28. References...
 BD CHAURASIA’S HUMAN ANATOMY
 NEUROLOGICAL EXAMINATION BY
NAVNEET KUMAR
 BICKERSTAFF’S NEUROLOGICAL
EXAMINATION
 NEUROLOGICAL EXAMINATION MADE
EASY – GERAINT FULLER
 PJ MEHTA’S PRACTICAL MEDICINE
 PRACTICAL PHYSIOLOGY – VD JOSHI
 WWW.GOOGLE.COM