Term | Definition |
Afferent | Ascending (towards the brain, inward) |
Efferent | Descending (away from the brain, outward) |
Auditory nerve enters cranium through the | Internal Auditory Meatus, synapses with cells of the Cochlear Nucleus in the brainstem |
Cochlear Nucleus | First auditory relay station found in the brainstem, tonotopically organized. It decodes basic signal features: timing, onset, intensity level, and sound localization on the vertical axis |
The Cochlear Nucleus projects to (4) | Superior Olivary Complex(mostly contralaterally), which then connects to the Inferior Colliculus; the Inferior Colliculus; the Reticular Formation, and the Facial Nucleus and the Facial Nerve |
Reticular Formation | Associated with alertness and response to stress (e.g. if there is an explosion nearby, you will wake up before perceiving the sound. Therefore if someone cannot perceive sound in the auditory cortex, they will still wake up) |
Facial Nucleus | If the sound is loud enough it will alert the facial nerve, causing musculus stapedius to contract and protect from loud sounds |
Superior Olivary Complex | made of several nuclei including the medial and lateral superior olive (the MSO and LSO respectively). It is important for sound localization on the horizontal access (Interaural Level Difference and Time Difference) |
Interaural Level Difference | LSO measures the ILD to get sound localization on the horizontal plane |
Interaural Time Difference | MSO measures ITD to get sound localization on the horizontal plane |
Inferior Colliculus | Major integrative station, collects info from several sensory systems. Sends from cochlear nucleus-->MGB-->PAC |
Medial Geniculate Body | Last of a series of processing centers along the auditory pathway from the cochlea to the temporal lobe of the cerebral cortex |
Primary Auditory Cortex | Lies on the temporal lobe at the Heschl's gyrus, where auditory sensations reach perception. Tonotopically organized, PAC involved in identifying and segregating auditory objects/scenes |
Oliviocochlear System | Efferent, MSO-->the myelinated Medial Oliviocochlear Fiber (MOC); LSO-->the unmyelinated Lateral Oliviocochlear Fiber (LOC) |
Medial Oliviocochlear Fiber | myelinated, projects to OHCs. Can release a chemical on OHCs that prevent electromotility, thus preventing amplification of a sound that is already loud. (cochlear suppression) |
Lateral Oliviocochlear Fiber | unmyelinated, projects to IHCs. Very thin, don't know much about them. (Afferent Excitation/Suppression) |