Aural Anaphysio Flashcards
What is the main function of the outer ear?
Sound funnel
Resonation
What is the function of the auricle or pinna?
The auricle or pinna, which funnels the sound to the ear canal helps localize sound (this is the most visible part of the ear and is composed primarily of cartilage)
What is the concha?
It is the entrance to the ear canal
Shell
How long is the external auditory meatus?
7 mm diameter
2.5 cm long, + 1.5 cm from tragus
What is the external auditory meatus made of?
lateral 1/3: cartilage
Medial 2/3: osseous-bony structure (temporal bone)
This selectively enhances sound
outer ear
What is the range where it is enhanced by outer ear?
sounds that are 1500 - 8000 Hz
What is the main function of the middle ear?
Answer: Increase the pressure towards the cochlea through impedance matching
Rationale
Impedance Matching:
The middle ear serves to match the high impedance of the fluid-filled cochlea to the low impedance of the air in the outer ear.
Sound travels through air, which has low impedance, but when it enters the cochlea (filled with fluid), it encounters higher impedance. If sound were transmitted directly from air to the fluid without amplification, much of the sound energy would be reflected rather than transmitted, leading to significant hearing loss. The ossicular chain (comprising the malleus, incus, and stapes) amplifies the sound vibrations from the tympanic membrane (eardrum) to the oval window (the entrance to the cochlea).
The malleus is larger than the stapes, which acts like a lever system:
The difference in size between the tympanic membrane (where the malleus is attached) and the oval window creates a pressure increase.
The surface area of the tympanic membrane is much larger than that of the oval window, allowing for an increase in pressure as the sound vibrations are transmitted.
Among the three bones of the ossicular chain, which one is the largest?
Malleus
Rationale: The first and largest of the three bones is the malleus (latin for hammer) because it resemble a hammer. One end of the malleus is embedded in the tympanic membrane. Because of this attachment, the vibrations of the tympanic membrae are transmitted to the malleus.
This bone in the middle ear is called the anvil. What is the name of this bone?
Incus
This is the border between the outer ear and middle ear
tympanic membrane
What is the tympanic membrane made of?
Composed of 3 layered sheets–epithelial lining of the EAM as the outer layer, middle layer (connective tissue that provides structure to the TM), inner layer is the lining of the middle ear
What is the main function of tympanic membrane?
transmits and amplifies the sound;
it transmits the sound from the outside coming into the inside and initates mechanical action of your ossicular chain/ middle ear.
Rationale
Vibration Response: The tympanic membrane vibrates in response to sound waves that enter the ear canal. These vibrations correspond to the frequency and amplitude of the incoming sound.
Transfer of Vibrations: The tympanic membrane transmits these vibrations to the ossicular chain (the malleus, incus, and stapes) in the middle ear, initiating the process of sound amplification.
When sound waves hit the tympanic membrane, it vibrates in response to the frequency and amplitude of the sound.
This vibration converts the airborne sound energy into mechanical energy.
This is the soft part of the tympanic membrane
Pars flaccida
What is the area of the tympanic membrane
55 m^2
What is impedance matching?
Impedance matching, we are trying to regulate the input coming into the ear in such a way that there is increasing force coming into the cochlea.
Impedance matching refers to the mechanism by which the outer and middle ear amplify and transfer sound waves effectively to the inner ear, where sound is converted into electrical signals for the brain to interpret
What is the first impedance matching?
Decreasing area
Rationale
Tympanic Membrane (55 mm2) vs Oval Window (3.2 mm2) (Inner Ear)
The tympanic membrane has a larger surface area compared to the oval window (about 20 times larger). This area difference results in an increased pressure on the oval window when the same force is applied, effectively amplifying the sound signal.
This alone provides a gain of approximately 25 dB (17:1).
Why is the area difference between the tympanic membrane and oval window important?
The tympanic membrane is significantly larger compared to the oval window, because this acts to increase pressure, effectively transferring energy more efficiently from the larger surface of the eardrum to the smaller surface of the oval window–greater pressure is generated on the surface with the smaller area.
What is the malleoincudal joint?
It is the saddle joint
Limited movement
The malleus and incus are connected in a tight joint (malleoincudal joint) that permits very little movement.
This provides a connection to the middle ear and inner ear
Footplate of the stapes
True or False. The footplate is the same size as the oval window
True (3.5 mm^2)
What is the second impedance matching?
Lever difference.
Manubrium (9mm) vs Long Process (7mm) = 2 dB
If the Manubrium and the Long process move, the force that’s produced at the end of the long process is amplified. This is because the manubrium is longer so the force that the long process receives is greater.
What is the least impedance matching?
Lever difference (2 dB)
What is the third impedance matching? What happens during the third impedance matching?
Tympanic Membrane Buckling
If the tympanic membrane receives sound, it will BUCKLE inward (like the photo above) while the manubrium pulls the TM inward as well.
Basically, the TM and the Malleus buckles. As they buckle, the distance traveled by the TM is longer than the Malleus.
Force Increase = 4-6 dB
When the tympanic membrane receives sound, it buckles inward, and the manubrium of the malleus is pulled inward as well. The distance the tympanic membrane travels is longer than the malleus, creating a mechanical advantage that results in a force increase of 4-6 dB. This contributes to the overall efficiency of sound transmission to the inner ear.
How much is the force increase of the third impedance matching?
4-6 dB
Why is impedance matching important?
Impedance matching is important in auditory systems because it helps to efficiently transfer sound energy from the air (which has low impedance) to the fluid-filled inner ear (which has high impedance).
How much is the total signal gain in impedance matching?
Total Signal Gain = ~31 dB
The tensor tympani is innervated by what cranial nerve? How about the stapedius muscle?
The tensor tympani is innervated by the CN V while the stapedius muscle is innervated by the CN VII
Where is the origin of the stapedius muscle?
Temporal bone
Where is the origin of the tensor tympani?
Eustachian tube/sphenoid bone
Where is the insertion of the stapedius muscle?
Post crus (stapes)
Where is the insertion of the tensor tympani?
Manubrium of the malleus
What is the function of the stapedius?
It rotates the footplate of your stapes posteriorly
They reduce the distance of the entire ossicular chain.
Protective for loud sounds–The stapedius muscle stiffens the ossicular chain so that its vibrations are reduced.
What is the function of the tensor tympani?
Pulls malleus anteriorly
They reduce the distance of the entire ossicular chain
Protective for loud sounds–the tensor tympani muscle tenses the tympanic membrane so that the vibrations are reduced
When a person hears very loud noises that could damage the ears, the middle ear muscles contract in a reflexive action called
When a person hears very loud noises that could damage the ears, the middle ear muscles contract in a
reflexive action called the acoustic reflex. The acoustic reflex stiffens the middle ear system, especially
the tympanic membrane.
What does the eustachian tube do?
Aeration of the middle ear space
Maintains equilibrium between middle ear and atmospheric pressure
What activates the eustachian tube?
Tensor veli palitini
The inner ear houses 2 sensory systems. What are they?
Vestibular system
Cochlea (hearing)
The inner ear consists of two labyrinths: What are the 2 labyrinths? Explain that each structure contains
Osseous (Petrous Portion of T Bone)
Membranous
The osseous (bony) labyrinth and the membranous labyrinth.
This is the entryway to the cochlea
Vestibule
Space for the middle ear
Round window
They are the sensory organs to detect balance
Semicircular canals
This semicircular canal detects the forward movement of the head such as nodding head up and down
Anterior Semicircular canal
The semicircular cancal detects the side to side movements such as shaking of head (e.g., shaking head no)
Lateral semicircular canal
Which semicircular canal detects head rotations such as tilting your head from shoulder to shoulder (e.g., cartwheel)
Posterior semicircular canal
This detects the acceleration
Utricle and saccule
This detects the acceleration vertically (e.g., free fall)
Saccule
This detects acceleration horizontally
Utricle