Exam #2 Flashcards
Where are other places in the ear, that we can find/ measure a simple periodic wave? (They all mimic a sound wave)
TM, malleus, incus, stapes footplate, basilar membrane, and (if it were possible) hair cell movement.
What three things are determined by impedence?
- Mass
- Stiffness
- Friction of the medium
What is the equation for The Area Trick or Condensation Effect?
Pressure (E) = Force (F)/ Area (A)
The labyrinth contains what two sensory systems?
Vestibular System & Auditory System
The membranous labyrinth portion of the cochlea consists of what two membranes?
Basilar Membrane & Reissner’s Membrane
The tympanic membrane is composed of what three layers?
The Epithelium, The Mucous Membrane, & The Fibrous Layer
What are the six surfaces of the tympanic cavity, what are they?
Superior, Inferior, Anterior, Posterior, Medial & Lateral
Where is the superior surface of the Tympanic Cavity, and what structures are located on the surface?
The superior surface means “above” or “on top”.
Structures: NONE!!
Where is the lateral surface of the Tympanic Cavity, and what structures are located on the surface?
Lateral means “Away from midline of the body”.
Structures: The lateral wall is made up by the tympanic membrane with a section of bone superior to it in the attic portion of the middle ear.
Where is the posterior surface of the Tympanic Cavity, and what structures are located on the surface?
Posterior means
Structures: 1) A prominence parallel in height to the oval window called the Pyramidal Eminence.
2) The stapedius muscle is housed/and passes through the pyramidal eminence into the middle ear.
Where is the medial surface of the Tympanic Cavity, and what structures are located on the surface?
Medial means “closer to midline of the body”
Structures: 1) Oval window
2) Round Window
3) Stapes Footplate
4) Annular Ligament (connects the stapes footplate to the oval window)
5)Promontory (The first basal turn is jutting into the promontory creating the bulging effect)
6) Facial Nerve ( 7th Nerve- Superior to the oval window hidden by small bony ridge.)
7) Chorda tympani (branch of the facial nerve passes through the ossicles.)
Where is the inferior surface of the Tympanic Cavity, and what structures are located on the surface?
Inferior means “lowest portion”, “below”, “bottom”, “under” or “beneath”.
Structures: NONE!! (Separates the middle ear from the jugular vein)
Where is the anterior surface of the Tympanic Cavity, and what structures are located on the surface?
Anterior means the “nearer the front, especially situated in the front of the body or nearer to the head”
Structures:
1. cochleariform process (pyramid/”volcano”)
2. tendon of the tensor tympani muscle (Runs along eustachian tube)
3. Eustachian Tube
Where is the eustachian tube located?
Anterior surface of the tympanic cavity.
What muscles participate in the acoustic reflex?
1) Tensor Tympani
2) Stapedius
What are the three functional subsystems of the auditory system?
1) Conductive
2) Sensorineural
3) Central
What are the functions of the Eustachian Tube?
1) Equalize air pressure on both sides of the TM.
2) Allows for the air supply that is essential to the metabolism of the tissues of the middle ear.
3) Aids in drainage of middle ear secretions into the nasopharynx.
What portion of the malleus attaches to the tympanic membrane?
Manubrium
What is the functions of the Conductive System?
Transmission & Impedence Matching
What does it mean to say that there is an impedence mismatch between the outside air and the inner ear?
A sound wave is generated in air, low impedence medium, and transmitted to the fluid-filled cochlea, a high impedence medium. When the transfer of of sound is made from the low impedence of the middle ear to the high impedence of the fluid, a great deal of energy must be lost.
What are the functions performed by the sensorineural system?
Transducer, Frequency Analyzer, & Transmission
How does the middle ear overcome impedence mismatch?
With the Area Trick or the Lever Trick.
How large is the impedence mismatch?
1) Expressed as a ratio:
2) Expressed on a dB scale:
1) 1/1000th (?)
2) -30 dB or 30 dB of loss
What does the superior wall separate in the tympanic cavity?
It separates the middle ear from the brain.
What does the inferior wall separate in the tympanic cavity?
It separates the middle ear from the jugular vein.
How does the eustachian tube of an infant compare to an adult? Why are these anatomical differences important?
A child’s eustachian tube is significantly shorter, wider, and straighter than an adults and therefore is much more susceptible to disruption of normal functioning, as well as to the spread of infection from the nose and throat, to the middle ear. (Hence, gravity does not help with drainage, therefore BAM otitis media)
What gap at the apex of the cochlea allows the fluid in the vestibular canal to communicate with the fluid in the tympanic canal.
Helicotrema
What material is a fatty substance that coats the fibers of some but NOT all neurons therefore speeding up the transmission of neural signals.
Myelin Sheath
The peripheral auditory system consists of everything from the pinna up to and including what?
The 8th Auditory Nerve
What do neurons have in common with toilets?
They both have refractory periods (a disappointing flush)
The Central Auditory system consists of structures in the what?
Brain stem & Auditory cortex
What is characteristic frequency?
(Best Frequency)
The sharp dip in each tuning curve represents the LOWEST threshold and therefore the frequency at which the neuron is MOST sensitive.
What does it mean to say that the auditory pathway exhibits tonotopic organization?
The relationship that exists on the auditory nerve between the CF and the physical location of the nerve fiber along the basilar membrane correspond.
What anatomical structure lies immediately above the superior surface of the tympanic cavity.
Epitympanic recess (Attic) AND Brain, dura, meninges.
What effects do thee contraction of the tensor tympani and the stapedius muscles have on the structures of the middle ear?
1) Stiffens the Tympanic membrane
2) Stiffens the ossicular chain.
What is the area of the TM?
0.594cm^2
What is the area of the stapes footplate?
0.032cm^2
How do you do the Area Trick/ Condensation Trick??
dB= 20log(0.594/0.032)
= 20log(18.6)
= 20(1.27)
=25.4 dB (This is how many dB we will gain back after the Area Trick/Condensation Effect)
Malleus is how much longer than the incus lever arm?
30%
The Lever Trick
The lever ratio is 1.3 : 1.0
dB= 20log*(1.3)
= 20 * (0.11)
= 2.3 dB
The total amount of decibels restored by the Area Trick and the Lever Trick=
(25.4 dB + 2.3 dB) = 27.7 dB
Give an example of of the difference between force and pressure:
A good example would be a dull knife and a sharp knife. The sharp knife has a smaller area while the dull knife has a larger area. Both can be pushed down to cut meat with the same amount of force, but only the sharp knife will cut through the steak due to a smaller area. It is important because the auditory system uses this same idea in the condensation effect. Sound is collected over a large area of the tympanic membrane and is transferred to an area 13 times smaller the stapes footplate. This causes a pressure to increase at the oval window, since the original force has remained unchanged, but the area has been reduced.
Frequency Response
F(1) = C/4*L F(2)= F(1)*3 F(3)= F(1)*5
What does it mean to say that the auditory system is a spectrum analyzer?
It means that the sensorineural mechanism of the auditory system breaks a complex sound into it’s individual frequency components. On the basilar membrane of the cochlea, high frequency components are interpreted near the base, where as, low frequency components are interpreted near the apex.
How many auditory nerve fibers are there? (per cochlea)
30,000 (~10 nerve fibers per IHC)
The cochlea contains roughly how many channels?
3,000-3,500
What is transduction?
Mechanical vibration that is converted into a series of impulses on the auditory nerve.
In depth explanation of transduction.
1) Vibration of basilar membrane will cause cilia to pivot at the base.
2) Sheering of cilia results in flow of electrical current through the hair cell called receptor current.
3) Receptor current stimulates release by the hair cell of neurotransmitter chemicals.
4) The uptake of neurotransmitter chemicals by dendrites in the 8th nerve fiber connected to the base of the hair cell, stimulates all-or-none action potential in the nerve fiber.
Transduction links:
Are filaments connecting cilia of different heights.
What attaches the basilar membrane to the cochlea?
Spiral Ligaments
Ganglion
Collection of cell bodies.
Most auditory nerve fibers synapse on
IHCs
Most auditory nerve fibers are
afferent
What specific component of the hair cell channel is ressponsible for transduction?
Inner hair cells
A hair cell channel consists of
1 IHC & 3 OHCs
Whether a nerve fiber fires or not depends on:
1) Time elapsed since the last time it fired.
2) The strength of the stimulus. (AKA how much neurotransmitter chemicals is dumped)
Whether a nerve fiber fires is:
Probablistic: All-or-none
Important hair cell properties:
1) graded/continuous (analog)
2) half-wave rectification
What is the largest amount of voltage you can have in your body?
140mv
What do the V & A systems have in common?
Common Fluid System
Hair Cell Motion Detectors
Innervation
Synchrony Theory
When nerve impulses are in sync from separate hairs.
