Outer and Middle Ear Flashcards
What are the two main functional purposes of the pinna?
Acts as an acoustical antenna to collect sound
Gain- low frequency filter/resonator tube
What are the major audiological consequences of pinna damage?
Mostly aesthetic consequences – i.e. microtia, macrotia, anotia
In children, the ear canal is roughly what direction? In adults?
Children - more horizontal
Adults - roughly perpendicular, slight downward
What is the general shape of the ear canal? What is it shaped like this?
Ear canal has two turns and is shaped like a lazy s
Protective
What portion of the ear canal is surrounded by cartilage? Bone?
Outer 1/3 of EAM cartilaginous
Inner has a bone
Cerumen is produced in what part of the ear canal?
Epidermal lining of the outer portion of the ear canal contains hair follicles and glands that secrete cerumen
What is the function of cerumen?
Protection - keeps from drying out, slight antibacterial functions, repel insects
The ear canal primarily acts like what kind of resonator?
Acts as an open-closed pipe resonator
Peak of filter is broadly tuned at closed end (TM is not completely reflective)
At what frequency is the primary resonance of the ear canal and meatus?
2 - 3 kHz
What parts of the body contribute to the resonances by the time one reaches the tympanic membrane?
Head torso and pinna
What portion of the Eustachian tube is surrounded by cartilage? Bone?
First 1/3 has a bony foundation, remaining 2/3 is cartilaginous
Isthmus is where they meet.
Which nerve runs next to the middle ear cavity?
Facial nerve (Vll)– runs along the posterior side of the ear canal
What is the promontory? What is its function?
The promontory is a rounded prominence formed by the lateral projection of the basal turn of the cochlea
Positioned to protect the oval and round windows in that it directly faces the middle ear cavity
What vein runs next to the inferior wall of the middle ear cavity? What type of tumor is common to destroy this wall?
Jugular vein
Glomus jugular
The children the Eustachian tube is roughly at what angle? In adults?
In adults- 30-45o angle from the anterior wall of the middle ear cavity to the posterior wall of the nasopharynx
Children - more horizontally positioned, lays almost parallel with the pharyngeal ostium
What are the names of the ossicles?
Malleus incus and stapes
The middle ear bones solve what major problem in the transduction of sound?
The impedance mismatch problem – transforming the signal from a medium of low impedance (air) to a medium with high impedance (cochlear fluid)
When sound wave meets a higher impedance medium, energy is normally reflected
What are the three mechanisms that the ossicles improve sound transduction?
- Area difference between the TM and the stapes footplate
- Lever effect that is provided by the ossicular chain
- Buckling effect of the ossicular chain
The tympanic membrane moves in what direction?
More movement at the inferior margin
Which of the ossicles is the weakest and most likely to break?
Incus – long process is the contact point for the stapes and is the weakest point in the ossicular chain
