Tuesday, April 2, 2013

Cochlear nerve, pathway and mnemonic

It's time to finish off the cochlear part of the vestibulocochlear nerve! :)

It starts off from the organ of corti, central processes of the spiral ganglion forms the cocchlear nerve and they terminate into the cochlear nuclei

From the cochlear nucleus, most of the axons cross to the opposite side in the trapezoid body and terminate in the superior olivary nucleus

The axons arising from the superior olivary nucleus form the lateral leminiscus
and reach the inferior colliculus

The fourth neurons pass through the inferior brachium to reach the medial geniculate body

The axons of the fifth neurons form the auditory radiation which passes through the sublentiform part of the internal capsule to reach the auditory area in the temporal lobe

How am I ever gonna remember all this? @_@
Mnemonic! =D
S = Superior olivary nucleus
L = Lateral leminiscus
I = Inferior colliculus
M = Medial geniculate body

I sorted out the whole pathway for you :P

Now, all you need to remember is that lesion in the cochlear part of the 8th nerve of the cochlear nucleus will cause a unilateral sensorineural hearing loss
Because fibres haven't crossed yet

If it is a bilateral senorineural hearing loss, the lesion is at higher levels such as the brainstem, thalamus or cortex
These patients will also have a decreased ability to localize a sound source

I'll add the mnemonic for the auditory tests here too

W, for Webers test, is a symmetrical alphabet ie made up of two V's
So it tests both ears simultaneously
Also, tuning fork is placed on the Vertex

R, for Rinnes test, is asymetrical
Tests only one ear
It's kinda stupid but works for me :)

That's all!

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