BPK 105 Study Guide - Midterm Guide: Ear Canal, Bony Labyrinth, Membranous Labyrinth
27 Apr 2018
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Module 5 - Review Questions - Part 4
8. Describe all the changes a sound wave goes through before it becomes a fluid wave
within the perilymph of the cochlea. Include the relevant anatomy in your description. [4
marks]
Perilymph: Fluid between the bony labyrinth and the membranous labyrinth of the inner ear.
The membranous labyrinth is filled with a clear fluid called endolymph, and the space between
the membranous and bony labyrinths is filled with a fluid called perilymph.
- Before sound waves become a fluid in the perilymph, sound waves in the air are picked
up by the external auricle and then directed into the external auditory canal.
- They travel through the external auditory canal before coming into contact with the thin
tympanic membrane (or eardrum).
- the vibrations felt in the membrane are transmitted further inwards, causing the three
auditory ossicles (malleus, incus, and stapes) to start vibrating, furthering the vibrations
deeper into the ear.
- Once the vibrations are transmitted to the last bone, the stapes, they then travel through
the base of the stapes to the oval window as the two are connected.
- As this transition occurs there is a 20 fold amplification of the vibrations due to the
dramatic decrease in area, however two small muscle serve to help mute the strong
vibrations and protect the delicate structure of the inner ear.
- Finally the vibrations in the foot plate cause the perilymph in scala vestibuli to begin
vibrating, carrying the fluid vibrations deeper towards the inner ear.
Hearing occurs in response to sound waves, and balance occurs in response to gravity or
motion.
-external ear: designed to capture sound waves and send them towards the tympanic
membrane (eardrum).
-The sound waves stimulate motion of the tympanic membrane, converting the
sound wave into motion.
- This motion is then transmitted through the middle ear via the auditory ossicles.
- These small bones, malleus, incus, and stapes, amplify their movement and push and
pull on the oval window of the inner ear.
- The motion of the oval window causes fluid waves to form in the inner ear.
- Through this mechanism, we can see that sound waves are converted to motion and
then back into waves, this time within the fluid of the inner ear.
- The fluid wave generated at the oval window then moves through the coiled structure of
the cochlea.
Document Summary
Module 5 - review questions - part 4: describe all the changes a sound wave goes through before it becomes a fluid wave within the perilymph of the cochlea. Perilymph : fluid between the bony labyrinth and the membranous labyrinth of the inner ear. The membranous labyrinth is filled with a clear fluid called endolymph , and the space between the membranous and bony labyrinths is filled with a fluid called perilymph . Before sound waves become a fluid in the perilymph, sound waves in the air are picked up by the external auricle and then directed into the external auditory canal. Once the vibrations are transmitted to the last bone, the stapes, they then travel through the base of the stapes to the oval window as the two are connected. Finally the vibrations in the foot plate cause the perilymph in scala vestibuli to begin vibrating, carrying the fluid vibrations deeper towards the inner ear.
