Lecture 3: Audition Flashcards
What is sound?
Pressure waves generated by vibrating air molecules
What are the 4 major features of sound?
- Waveform
- Phase
- Amplitude
- Frequency
Perception of sound corresponds to___________and ___________ .
loudness, pitch
What is amplitude perceived as? What is its unit of measurement?
- loudness (a measure of the size of the pressure fluctuations)
- decibels
What is frequency perceived as? What is its unit of measurement?
- pitch (a measure of the rate of the vibratory cycles that occur in one second)
- hertz (Hz)
Undisturbed air molecules are at _____ or ______ pressure
ambient, atmospheric
What is it called when the prong of a tuning fork moves to the right causing the neighboring air molecules to be pushed together?
compression or condensation
Define pure tones
sounds produced by objects vibrating in simple harmonic motion
How is sound wave propagated through the air?
- Each particle oscillates around its own position
- However, the sound wave moves through the air as each particle sets its neighbor in motion
What is simple harmonic motion also known as? What does it generate?
- aka sinusoidal motion
- generates a sine wave
At what amplitude is sound painful?
120-140 dB
At what amplitude is sound an uncomfortable loudness?
100 dB
How many hertz (frequency) is the most sensitive thresholds?
2000 - 5000 Hz
What are the functions of the external ear?
- Protection
- Sound gathering providing a high-frequency boost >3k Hz
- Sound localization & elevation detection (Alters the effective spectrum of sound in a manner dependent on the location (up or down) of the sound source in the vertical plane)
What is the smallest bone in the body?
the stapes
What is the function of the stapes?
Pounds on the oval window to send signals to the inner ear
What is impedance matching?
The middle ear matches low-impedance airborne sounds to the higher-impedance fluid of the inner ear
What is impedance?
a medium’s resistance to movement
How would impedance matching affect the ear is there is no middle ear?
- 30 dB loss intensity
- Example from powerpoint: Sound vibrations traveling directly from air to water would be reflected and undergo a 30dB loss in intensity
How is impedance matching affected with the middle ear?
- Ear gains 34bB from the middle ear
- Area advantage = 27 dB
- Ossicular lever action = 1.3 dB
- Curved membrane buckling mechanism = 6 dB
What is the function of the inner ear?
site for transduction of sound pressure waves to action potentials in the 8th nerve
What is perilymph (located in the scala vestibuli of the cochlea)?
- Similar to other extracellular fluid (0 mV, low K+)
- Rich in Na+, low in Ca2+ and K+
What is endolymph (located in scala media of the cochlea)?
- Has high K+, low Na+, low Ca2+ concentrations (+80mV) due to the stria vascularis
What parts of the basilar membrane is the most stiff and the least stiff?
- Stiffest at base
- Least stiff at apex
Where do high frequencies cause vibrations on the basilar membrane?
High frequencies = base
Where do low frequencies cause vibrations on the basilar membrane?
Low frequencies = apex
What makes up the organ of Corti?
- Basilar membrane
- 3 rows of outer hair cells
- 1 row of inner hair cells
- Supporting cells
What innervates the inner hair cells of the organ of Corti
Sensory = innervates 8th nerve afferents
What innervates the outer hair cells of the organ of Corti?
- Amplifiers
- Receive efferent innervation that can modify the sound
What is the organ of Corti? What is its function?
- Auditory receptor organ on basilar membrane
- Respond to sound-induced vibrations of less than a nanometer
What occurs before the hair cells are activated?
- Tympanic membrane set into vibration by sound
- Stapes footplate moves in and out of the oval window
- Basilar membrane moves up and down
Explain the excitation (activation) of outer hair cells
When the basilar membrane moves in the upward direction, a shear force is generated between the reticular lamina and the tectorial membrane
- Stererocilia (connected by tip links) bend in the lateral direction (toward outer wall of the cochlea)
- K+ current depolarizes the cell and opens voltage dependent Ca2+ channels = transmitter release
- Ca2+ dependent K+ channels open = repolarization
Explain inhibition of hair cells
- Basilar membrane moves in the downward direction = stereocilia bend in the medial direction (toward the modiolus)
- Medial bending closes the MET (mechanoelectric transducer) channels and repolarizes/inhibits the hair cells
What is the motor activity of the OHCs known as?
cochlear amplifiers or active process in the cochlea
What are the inner hair cells of the cochlea known as?
sound transducers
What is the shape of the outer hair cells of the cochlea?
cylindrical in shape
What is the shape of the inner hair cells of the cochlea?
flask shaped
What is the shape of the inner hair cells of the cochlea?
flask shaped
What occurs to OHC when activated?
change in length by stretching the Prestin protein in its cell body
What do the OHC do during the excitatory phase (upward movement of basilar membrane)?
cell shortens = makes it easier for basilar membrane to overcome frictional forces that resists its upward movement
What do the OHC do during the opposite/inhibitory phase (downward movement of the basilar membrane)?
cell elongates = exerting an extra force on the basilar membrane
OHCs contract with _______
depolarization
What is the most common type of permanent hearing loss?
Occurs when there is damage to the OHCs and the “cochlear amplifier” is lost
Explain the transduction of IHC
- Activation of an IHC causes a chemical reaction in the cell
- Reaction causes neurotransmitter release at base of the IHC
- Neurotransmitter activates auditory neuron (CN VIII)
- IHC transduce mechanical vibrations into neural signals
The inner hair cells innervate ______ nerve fibers
auditory
What is the characteristic frequency?
The frequency of greatest sensitivity for the fiber
Where do the auditory nerve fibers come from? What do they form?
- From all parts of the cochlea and come together in the modiolus
- Forms the cochlear portion of CN VIII (auditory nerve)
- Afferent
- Associated with IHC
Are the auditory nerve fibers Type I or Type II fibers?
Type I
What is the function of Type II fibers? Are they associated with IHC or OHC?
- Efferents that can modify sound
- Associated with OHC
List in order the central auditory pathway (6)
- Auditory nerve
- Cochlear Nucleus (CN)
- Superior Olivary Complex (SOC)
- Inferior Colliculus (IC)
- Medial Geniculate Body (MGB)
- Auditory Cortex
Which structure in the central auditory pathway is the 1st auditory nucleus?
Cochlear nerve
Where is the cochlear nucleus located?
Medulla (brainstem)
The cochlear nucleus is uniaural. What does this mean?
It receives input from one ear
What are the 2 main functions of the cochlear nucleus?
- relays signals to the SOC (without processing)
- analyzes complex signals and sends this information to IC
Where is the superior olivary complex (SOC) located?
pons (brainstem)
The SOC is binaural. What does this mean?
It receives input from both ears
The SOC has 2 nuclei that are involved in ___ ______.
sound localization
What are the 2 structures that are a part of the SOC?
- Lateral Superior Olive (LSO)
- Medial Superior Olive (MSO)
What is the function of the LSO? What structure is it a part of?
- localization of high frequency sounds
- uses interaural SOUND level differences = louder when travels to one ear and dampens/softens as sound travels to other ear
- Part of the SOC
What is the function of the MSO? What structure is it a part of?
- localization of low frequency sounds
- uses interaural time differences
Where is the inferior colliculus located?
midbrain (brainstem)
The inferior colliculus (IC) combines _____information (from SOC) with information about _____sounds (from CN)
- spatial information
- complex sounds
The inferior colliculus with the superior collicus coordinates _____ and _ responses to enviromental stimuli. HIGH YIELD
- auditory
- visual
What kind of response does the IC mediate to sound?
head-turn response
What kind of reflex is the IC involved in? Provide an example.
- Auditory reflexes
- Auditory startle reflex = loud sound causes large scale muscle contraction
Where is the medial geniculate body (MGB) located?
thalamus (“gateway to the cortex”)
The MGB receives the most input from the ___ and projects to the _____ cortex.
- IC
- auditory
What is the function of the MGB?
relay station for information going up to (or down from) the auditory cortex
All nuclei contain ______ maps.
tonotopic = cells arranged in order of best stimulus frequency
Nuclei involved in sound localization also contain maps of ____ _____.
spatial location
Which structure has the highest level of sound processing?
auditory cortex
What structure does the MGB project to?
primary auditory cortex (AI)
What structure do secondary projections from AI project to?
secondary auditory cortex (AII) & other association areas
Which structure does the auditory cortex receive input from?
medial geniculate complex
The primary auditory cortex (AI) has a _ organization.
tonotopic
What are the functions of the auditory cortex? (5)
- mediate auditory memory
- perform complex auditory discriminations (including speech discrimination)
- use spatial information regarding the location of a sound source to mediate appropriate (non-reflexive) motor responses
- mediate the formation of concepts about auditory stimuli
- perform difficult auditory tasks
Efferent auditory nerve fibers are a part of the “ ______ ______” that descends fron the _______ to the ______.
- olivocochlear bundle
- SOC
- cochlea
What is the function of the olivocochlear bundle?
modulates activity of the hair cells
What are the 2 components of the olivocochlear bundle? What do they innervate?
- UOCB (uncrossed olivocochlear bundle) = LSO = inner hair cells on the same side
- COCB (crossed olivocochlear bundle) = MSO = outer hair cells on the opposite side
What is the function of the COCB of the SOC neurons?
- targets outer hair cells = dampens their “amplifying” action
- These reflex attenuations primarily for mid to high frequency sounds
- Important for hearing in background
The human ear is most sensitive to sounds at which of the following frequencies?
A. 150 Hz
B. 1,500 Hz
C. 3,500 Hz
D. 7,500 Hz
c. 3,500 Hz
A 21-year-old wrestler presents to his Otorhinolaryngologist (ENT) following a severe injury to the right ear which has caused difficulty hearing. The ENT believes the impact may have altered the patient’s ability to match impedance. If so, which of the following structures was likely damaged?
A. Pinna
B. Tympanic Membrane
C. Scala Media
D. Organ of Corti
b. Tympanic membrane
Outer hair Cells (OHC) play an important role in the amplification of sound by altering its length during periods of excitation and inhibition. Which of the following proteins is responsible for these changes?
A. Prestin
B. Actin
C. Myosin
D. Tip Links
a. Prestin
Inner hair cells (IHC) transduce mechanical vibrations into neural signals via which of the following cranial nerves?
A. CN IV
B. CN V
C. CN VII
D. CN VIII
d. CN VIII (Vestibulocochlear)
A 43-year-old man presents to the ED following strange neurological symptoms likely associated with a stroke. If MRI confirms a lesion in the Lateral Superior Olive (LSO), which of the following would likely be impacted?
A. Ability to localize high frequency sounds using sound level differences
B. Ability to localize low frequency sounds using time differences
C. Ability to localize high frequency sounds using time differences
D. Ability to localize low frequency sounds using sound level differences
a. Ability to localize high frequency sounds using sound level differences
