Question

Put the following items in order from the flow of sound waves to the production of action potential to the destination in the brain.

auditory association area
auricle

basilar membrane

cochlea

cochlear branch of CN VIII

external acoustic meatus

incus

inner hair cell  

malleus     

oval window

primary auditory cortex

scala vestibuli

stapes

synapse in inferior colliculus

synapse in medulla oblongata

synapse in thalamus

tympanic membrane

Answer 1

Auricle ----> External acoustic meatus -----> tympanic membrane ------>malleus -----> stapes ----> Oval window

---->Cochlea -----> scala vestibuli -----> Bailar membrane ------> inner hair cells ----> cochlear branch of CN VIII

---> synapse in medulla oblongata ----> synapse in inferior colliculus ----> synapse in thalamus -----> primary

auditory association area

Auditory Pathway -

The external ear/pinna funnels sound waves direct it into the auditory canal. This sound then reaches the tympanic membrane, and causes it to vibrate.

The handle of the malleus articulates with the tympanic membrane, and the malleus also has an articulating facet for the Incus. The incus articulates with the stapess.

The stapes is shaped like a stirrup, and impacts with oval window. The stapes moves like a piston, and causes the oval window to move in and out with sounds.

The sound waves are sent up the scala vestibuli to the apex of the cochlear duct (the helicotrema). Here it continues back down the spiral shaped cochlear organ in the scala tympani. Scala media and scala tympani below are separated by the basilar membrane.

When these waves move up and down the perilymph in the scala vestibuli and scala tympani, the vibrations move the basilar membrane.

The organ of Corti lies on the basilar membrane, convert these vibrations into electrochemical signals, then it is transmitted to inner hair cells. The influx of potassium causes the generation of a local current and then an action potential that is sent up the cochlear division of the vestibulocochlear nerve . This nerve then sends the signal to nuclei in the brainstem.

The superior olivary complex - This is a cluster of nuclei found in the brainstem.

The inferior colliculus - This is the ultimate end point of many of the brainstem nuclei outputs.

The medial geniculate nucleus - This is the nucleus of the thalamus that acts as the relay point between the inferior colliculus and the auditory cortex.

The primary auditory cortex - This is located in the temporal lobe and has a role in the processing of auditory information. It lies in the superior temporal gyrus of the lobe,