Vestibular cochlear nerve

The nerve leaves the anterior surface of the brain between the lower border of the pons & the MO
The nerve is concerned with transmitting afferent information from the internal ear to the CNS

Vestibular nerve nuclei and their central connection

Cochlear nerve and their central connections

Vestibular nerve

Cochlear nerve

The vestibular nuclear complex has 4 nuclei (Lateral, Superior, Medial & Inferior)
Afferents
1. Conduct impulses from the utricle & saccule that provide information about the position of the head
2. Conduct impulses from the semicircular canals that provide information about the movements of the head
Efferents from nuclei
1. To cerebellum via inferior cerebellar peduncle
2. To spinal cord via vestibular spinal tract (Uncrossed)
3. To 3, 4 & 6 nerves via medial longitudinal fasciculus
4. To the cerebral cortex through VP nuclei of the thalamus
Functions
1. Enable the movements of the head & the eyes to be coordinated – Maintain visual fixation
2. Maintain balance by influencing muscle tone of limbs & trunk

Conducts nerve impulses concerned with sound from the organ or Corti in the cochlea
There are 2 cochlear nuclei (Anterior & posterior)
The 2 nuclei are situated on the surface of the inferior cerebellar peduncle
Ascending auditory tract (Lateral lemniscus) sends information to 1stry & 2ndry auditory cortex on both sides of the brainstem (Mainly in the contra lateral side)
1stry auditory cortex : On the superior temporal gyrus
2ndry auditory cortex : responsible for recognition & interpretation of sounds on the basis of past experience
Descending auditory pathway ends on the hair cells of the organ of Corti (Feedback mechanism & inhibit the reception of sounds)

Examination of the vestibular cochlear nerve : Cochlear component

Whispering test

Test by whispering numbers into one ear while masking the hearing of the other ear
If the hearing is impaired, examine the external meatus & the tympanic membrane with auroscope to exclude wax & infection

Differentiate conductive (Middle ear) deafness & perceptive (Nerve) deafness

Weber’s test

Hold the base of a vibrating tuning fork (256 or 512 Hz) on the vertex
Ask the patient if the sound is heard more on one side
In conductive deafness : Sound is louder in the affected ear (External distraction is reduced)
In nerve deafness : Sound is louder in the normal ear

Rinne’s test

Hold the base of a vibrating tuning fork against the mastoid bone & ask the patient if note is heard
When note disappears – Keep the tuning fork in front of the external meatus
Patient should hear the sound again (If normal), because air conduction is better than bone conduction

Interpretation

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