The first-order axons entering the brainstem from the cochlea terminate ipsilaterally on the dorsal and ventral cochlear nuclei. From here, second-order axons have several synaptic targets. Second-order axons forming the ascending auditory pathway ascend to the pons and project bilaterally on the superior olivary nucleus (eFig. 9.82). These bilateral projections are important for auditory acuity and localizing the origin of a sound. From here, fibers continue to ascend as the lateral lemniscus and terminate in the inferior colliculus of the midbrain. Axons leaving the inferior colliculus then have a synaptic relay in the medial geniculate nucleus of the thalamus before reaching the final synaptic target: the primary auditory cortex (superior temporal gyrus) of the temporal lobe (eFig. 9.82). Throughout this pathway, from the basilar membrane to the primary auditory cortex, auditory stimuli are tonotopically represented. This is analogous to the somatotopic map previously discussed in the section on somatosensory systems pathways.