Fig. 1.
Sketch of the anatomy surrounding the auditory nerve. External electrical conductance along the auditory nerve changes (i) when it exits the internal auditory meatus (IAM, a canal in the temporal bone for the auditory nerve, the vestibular nerve and the facial nerve) into the subarachnoid space and (ii) when it subsequently enters the brainstem. The respective discrete conductance interfaces are between (temporal bone + dura mater)/CSF and CSF/brainstem (marked by dashed lines). The dura mater marked by arrowheads covers also the IAM (Lescanne et al., 2002) and due to its similar conductance to bone, together they electrically form a single macroscopic compartment. Redrawn after Martin et al. (1995) who compared the passage of the human auditory nerve from IAM to brain with and without CSF (air) and found evidence that the left border (left arrow) is the generator of the first negative ABR peak, In, whereas the CSF/brain border causes ABR peak II.