Lecture 6 Flashcards
What is bigger typanic membrane surface or area of stapes?
Tympanic membrane surface area is about 17 times that of the surface area of the stapes… 55mm to 3.2 mm -This increases the force from the ossicular lever system to the cochlear fluid by 22X -Fluid has greater inertia than air and requires this increase in force in order to cause vibration in the fluid
What is the conduction pathway sequence?
tympanic membrane… malleus…. incus…. stapes…. oval window
What do tympanic membrane and auditory ossicles provide?
the impedance matching btw the air and the fluid
How would hearing sensitivity be affected in the absence of the ossicular system and the tympanic membrane?
….
What does the tympani muscle do?
pulls handle of malleus inward
What does the stapedius muscle do?
pulls stapes outward
What effect do the above two opposing forces cause the ossicular system?
…
What is the function of this system( the attenuation reflex)?
…
What effect do these two muscles have on a person’s sensitivity to his or her own speech?
…
What consists of three side by side coiled tubes?
cochlea
What are the major components of the cochlea?
scala vestiviuli scala media scala tympani reissner’s membrane
What does the Reissner’s membrane do? (vestibular membrane)
separates scala media from scala vestibuli
What does the reissner’s membrane maintain?
a special fluid within the scala media
Because of the thinness of Reissner’s membrane?
the scala media and vestibuli are considered to be a single chamber as far as sound conduction is concerned
What does the basilar membrane separate?
scala media from scala typani
What does the basilar membrane consist of?
contains 20,000 to 30,000 fibers that project from the modiolus of the cochlea to the outer wall
Can the fibers of the Bailar membrane vibrate?
Yes
How are the fibers in the basilar membrane attached?
Distal ends of the fibers are not fixed but are embedded in the basilar membrane.
What does the length of the basilar fibers do from the oval window to the apex of the cochlea (helicotrema)?
the length increases
What happens to the length of the fibers from the oval window to the apex of the cochlea?
The fibers decrease.
What is the result of the short fibers near the oval window?
The stiff short fibers near the oval window be at a high frequency
What is the effect of the long fibers near the oval window?
The long limber fibers near the apex of the vibration at a low frequency.
Where does the high-frequency residents of the basilar membrane occur?
Near the base
Where does the low-frequency residents of the basilar membrane occur?
Near the apex helicotrema
What does the organ of corti generate?
It generates the nerve impulses in response to vibration of the basilar membrane
What are the sensor receptors of the organ of Corti
hair cells
Single row of internal hair cells:
3500;12 um dia
3-4 rows of external hair cells
12000; 8 um dia
What does the hair cells stimulate in the organ of Corti
Hair cells stimulate nerve fibers that lead to the spiral ganglion of corti
What do stereocilia from the hair cells do?
touch or are embedded in the overlying tectorial membrane
What does bending of the hair do?
Bending of the hairs in one direction depolarizes them and bending them in the opposite direction hyperpolarizing them
What creates a rigid unit in the organ of Corti
Outer ends of hair cells are tightly attached to reticular lamina, supported by rads of Corti, which are attached to the basilar fibers
What do you neurons in the ganglionic of the organ of corti do?
The ganglion send axons via the cochlear nerve (CN VIII) into the upper level of the medulla
What does movement of the basilar fiber cause movement of?
the reticular lamina
What does movement of the reticular lamina cause?
shearing forces on the hair cells against the tectorial membrane
So whenever basilar membrane moves?
hair cells become excited
What has about 100 sterocilia on the apical border?
each hair cell
Where are stereocilia longer?
on the side farther from the modiolus
When cilia are bent in direction of the longer ones??
a tensile force is created on the shorter cilia
What does the tensile force cause?
A mechanical transduction that opens 200 to 300 potassium channels resulting in a depolarization of the hair cell membrane
What is the scala media filled with?
endolymph
What are the scala vestibuli and scala tympani filled with?
perilymph
What does endolymph contain?
a high concentration of potassium and a low concentration of Na (opposite that of the perilymph)
+ 80 mv difference btw endolymph and perilymph (scala media is positive) =
endocochlear potential
Tops of hair cells project through the reticular lamina and are bathed by?
endolymph
What are lower bodies of the hair cells surrounded by?
perilymph
What is the intracellular potential of hair cells?
-70 mv with respect to perilymph -150 mv w respect to endolymph
How does nervous system detect sound frequencies?
by determining positions along the basilar membrane that are most stimulated
Explain how the auditory system determines loudness
…
what is a decibel
…
describe the relationships btw frequency and pressure in decbels
…
how does the frequency range that can be heard change w age?
…
What are components of the auditory nervous system pathway?
spiral organ of corti dorsal and ventral cochlear nuclei superior olivary nucleus lateral lemniscus nucleus medial geniculate nucleus (thalmus) auditory cortex
Where does decussation occur btw right and left pathways
…
what is the relationship btw the auditroy tracts and the RAS
?
where is the auditory cortex located?
..
Distinguish btw the primary auditory cortex and the auditory association areas
…
explain how a person determines the direction from which sound comes
…
Look at all diagram and pictures of lectures.
…
