[Note: Mr. Friend, you told us not to go into detail and I understand that it is not on the syllabus. But the content of the second video was quite interesting and the pieces sort of fit together a bit better with some detail so I went into a little bit of detail. ]
the ear converts sound waves in the air into electrical impulses which can be interpreted by the brain.
As sound enters the ear it asses through the external auditory canal where it meetings the tympanic membrane.
The tympanic membrane then vibrates in response to the sound.
Sounds of a lower frequency produce a slower rate of vibration and sounds of a lower volume or amplitude produce a less dramatic vibration.
higher frequency sounds produce FASTER vibrations.
the tympanic membrane is cone shaped and is connected to 3 bones collectively known as the auditory ossicles. They consist of the malleus, the incus and the stapes.
The movement of the tympanic membrane causes the ossicles to vibrate passing on the information of the sound wave (frequency of amplitude).
The three bones pivot together on an axis. The pivotal axis is due to a series of ligaments which hold the bones in place within the middle ear cavity (space). The two main ligaments are the malleal ligament and the posterior costal ligament.
The vibrations are transmitted eventually to the footplate of the stapes.
The stapes moves with a piston like action which sends vibrations into a bony labyrinth.
The labyrinth is filled with a fluid called perilymph. It is important because if the bony structure was closed and inflexible then the stapes movement would be unable to displace the perilymph and vibrations would be unable to be sent.
Due to the flexibility of a membrane called the oval window. The stapes movement can displace the perilymph allowing vibrations to enter the labyrinth.
The corridor leading to the round window (one of the two openings of the inner ear) is found within the spinal portion of the bony labyrinth (called the cochlea). --> snail shaped structure.
Vibrations are produced by the stapes and are drawn into the spiral system and is sent through the round window for the vibrations to dissipate in the inner ear.
Portion of the passage by which vibrations travel have names:
-vibrations ascend via the scale of vestibule
-vibrations descend via the scale of timpani.
in between is the cochlea duct-filled with a fluid called endolymph. The membrane within the duct is flexible and thus respond to vibrations and send the vibrations back down the scale of timpani where it is directed to be dissipated via the round window.
There are two portions of membrane in the cochlea duct. The top part is called the reissner's membrane and the bottom portion of the membrane is known as the basilar membrane.
Within the basilar membrane sits the organ of corti.
The nerve impulses are actually generated by specialized cells WITHIN the organ of corti called hair cells. The hair cells are covered by a membrane called the tectorial membrane. As the basilar membrane vibrates the hair cells are pushed up against the tectorial membrane causing the hair cell to generate an AP or nerve impulse to the brain via the auditory nerve.
The entire basilar membrane does not vibrate evenly it depends on the frequency of the sound waves. A high frequency will result in the lower portion of the basilar membrane near the base of the cochlea to vibrate and a lower frequency will result in the higher portion (near the apex) of the basilar membrane to vibrate.
Source: Auditory Transduction- YouTube-flv
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