Note: A good way to remember what information passes through each geniculate body is that music goes to medial and light goes to lateral. Projections from the medial geniculate body proceed then to the primary auditory cortex. The MGB does not act as a simple relay centre: it has reciprocal connections with the auditory cortex and mediates refinement of the incoming information. These fibres project to the ipsilateral medial geniculate body (MGB) in the thalamus (recall that vision is relayed on the lateral geniculate body). Inferior Colliculus and Medial Geniculate Bodyįibres ascending through the lateral lemniscus from both cochlear nuclei and from the superior olivary nuclei arrive at the inferior colliculus, where all these fibres carrying auditory information converge. Therefore, hearing problems can be conductive or sensorineural but are rarely central.Īdobe Stock, Licensed to TeachMeSeries Ltdįig 3 – Information from each cochlear nucleus is transmitted bilaterally. above the level of the cochlear nucleus) will not lead to serious hearing impairment. This is important because supranuclear lesions (i.e. For that reason, information from both ears travels bilaterally in each lateral lemniscus. In summary, in both the dorsal and ventral nuclei, some fibres decussate while others do not.
It also projects upwards through the lateral lemniscus. The superior olivary nucleus is located just next to the trapezoid body. Although the ventral cochlear nuclei neurons decussate at the trapezoid body, some fibres synapse at the ipsilateral superior olivary nucleus. However, most fibres from the ventral cochlear nucleus decussate to the contralateral superior olivary nuclei in a region known as the trapezoid body. Other fibres ascend in the ipsilateral lateral lemniscus.įrom the ventral cochlear nucleus, some fibres also ascend in the lateral lemniscus bilaterally. It forms a small bulge on the surface of the brainstem – known as the auditory tubercle.įrom the dorsal cochlear nucleus, most fibres cross the midline and ascend in the contralateral lateral lemniscus.Dorsal (posterior) cochlear nucleus – located posterior to the inferior cerebellar peduncle.Ventral (anterior) cochlear nucleus – located in the area where the nerve enters the brainstem.Cochlear Nucleiįibres from the cochlear nerve bifurcate and information is sent to the cochlear nuclei on each side of the brainstem: The first order neurons synapse at the ipsilateral cochlear nuclei.īy OpenStax College, via Wikimedia Commonsįig 2 – The spiral ganglion houses the cell bodies of the first order neurones in the auditory pathway.
For more information on the vestibulocochlear nerve, its anatomical course and function please read this article. The nerve enters the cranium through the internal acoustic meatus and travels a short distance (around 1 cm) to enter the brainstem at the cerebellopontine angle. This proximity is clinically relevant since lesions to this nerve will usually produce symptoms in both the auditory and vestibular components. The vestibular nerve joins the cochlear nerve entering the internal acoustic meatus, and from this point onward they are collectively called vestibulocochlear nerve. Their central axons form the main component of the cochlear nerve. These neurones receive information from hair cells in the Organ of Corti and travel within the osseous spiral lamina. The spiral ganglion houses the cell bodies of the first order neurons (ganglion refers to a collection of cell bodies outside the central nervous system).
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