Exam #6: Auditory System Flashcards
What is sound i.e. what is the physical stimulus for audition?
Periodic condensation and rarefaction of air molecules
*****Note you need a higher frequency tuning fork compared to vibratory sense
What is a dB?
0.0002 dyne/cm2
What is the frequency range of human hearing? What is the normal human hearing range? How does the normal hearing range change with age?
Absolute Range= 20 Hz - 20 kHz (cycles per second)
Normal= 20Hz to 16kHz
**There is a decline in ability to hear higher frequencies with age, called presbycusis
What is the pressure range of human hearing?
0 dB- ~130 dB
What is a notch in an audiogram? What causes this notch?
Frequency at which the a sound need to be much more powerful to be heard compared to adjacent frequencies in that range
**Caused by a v. loud sound that kills hair cells e.g. explosion, gunshot….etc.
Describe the transduction of sound from outer ear to inner ear.
- External ear directs sound waves into the auditory canal
- Auditory canal transmits sound waves to the TM
- Sound waves move TM, which moves the chain of ossicles
- Footplate of the stapes is pushed into the oval window, which displaces fluid in the inner ear
What part of the auditory system facilitates the equalization of pressure?
Eustachian tube
What nerves innervate the inner ear muscles?
CN V & VII
What is the function of contracting the inner ear muscles?
Protection from loud sound i.e. attenuation reflex
What is the afferent limb of the middle ear attenuation reflex?
CN VIII
What is the efferent limb of the middle attenuation reflex?
CN VII to stapedius m.
CN V to tensor tympani
Lesion of what nerve/ accompanying muscle are responsible for the hyperacusis seen in Bell’s Palsy?
CN VII & stapedius m.
What is the Organ of Corti? What are the different parts of the Organ of Corti? What membranes separate these three different regions
The Organ of Corti is the sensory transduction apparatus for audition in the cochlea of the inner ear. It contains: Scala vestibuli --Reissner's membrane Scala media --Basilar membrane Scala Tympani
What fluid-type is in each region of the inner ear?
Scala vestibuli= Perilymph
Scala media= Endolymph
Scala Tympani= Perilymph
What produces endolymph?
Stria vascularis
Where is the base of the auditory hair cells (stereocilia)? What membrane are the tips of the auditory hair cells embedded in?
Base= Basilar membrane of the Scala Media Tip= Tectorial membrane of the Scala Media
Outline the steps of auditory transduction.
1) Sound waves
2) Vibration of organ of Corti
3) Bending of cilia in Scala Media
4) Change in K+ conductance to cause depolarization & hyperpolarization
5) Oscillating receptor potential i.e. cochlear microphonic
6) Glutamate release
7) Action potential
What is the difference between inner & outer hair cells
?
Inner= actual sensory receptors
- Fewer
- Single row
Outer=
- More
- Parallel rows
What frequency of sound is heard at the base of the cochlea?
High 1,600 Hz
What frequency of sound is heart at the apex of the cochlea near the helicotrema?
Low 25 Hz
Outline the pathway of auditory input.
1) Cochlea
2) CN VIII
3) Dorsal & ventral cochlear nuclei (medulla)
4) Lateral lemniscus
5) Inferior colliculus
6) Medial geniculate nucleus of thalamus
7) Auditory cortex
What is efferent control?
Olivocochlear bundle in the superior olivary complex sharpens frequency
How do we know if the sound comes from the right or left?
LSO neurons encode sound location based off sound intensity
**Lateral superior olive
For low frequency sounds, how do you determine location?
Time of arrival
