Auditory Senses (Lec 6) Flashcards
What is the conduction pathway sequence?
tympanic membrane, malleus, incus, stapes, oval window
The tympanic membrane surface area is about 17 X that of the surface of the stapes. This increases the force from the ossicular lever system to the cochlear fluid by how much?
22X; fluid has greater inertia than air and requires this increase in force in order to cause vibration in fluid
What do the tympanic membrane and auditory ossicles provide?
the impedance matching between the air and fluid
Tensor tympani is a small muscle in the ear, what does it do?
pulls handle of malleus inward
What does the stapedius muscle do?
pulls stapes outward
What are the major components of the cochlea?
scala vestibuli, scala media, scala tympani, reissner’s membrane; these make up the three tubes
What two structures does Reissner’s membrane separate?
scala media from scala vestibuli
What two structures does the basilar membrane separate ?
scala media from scala tympani
The basilar membrane contains 20,000 to 30,000 fibers that project from the modiolus of the cochlea to what?
the outer wall
Distal ends of the fibers are not fixed but are embedded in the basilar membrane, which allows the fibers to ____
vibrate
Describe how the length and diameter of the basilar fiber changes between oval window and apex of cochleas
length increases from the oval window to the apex of the cochlea
diameter of the fibers decrease from oval window to the apex of the cochlea
Where does high frequency of the basilar membrane occur?
near the oval window
where does low frequency of the basilar membrane occur?
near the apex of the cochlea
What is the function of the organ of corti?
generates nerve impulses in response to vibration of basilar membrane
What are the sensory receptors of organ of corti?
hair cells
Bending of the hairs in the organ of corti in one direction depolarizes them and bending them in the opposite direction does what?
hyperpolarizes them
Neurons in the ganglion of the organ of corgi send axons via the cochlear nerve into where?
the upper level of the medulla
Whenever basilar membrane moves, hair cells become ___
excited
Each hair cell has about how many sterocilia on its apical border?
100
Sterocilia are 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. This creates a mechanical transduction that opens what?
200-300 K+ channels resulting in depolarization of the hair cell membrane
What is endolymph?
fills scala media; endolymph contains a high concentration of K+ and a low concentration of Na+
Tops of hair cells project through the reticular lamina and are bathed in what?
endolymph
Lower bodies of hair cells are surrounded by what?
perilymph
What are the intracellular potentials of hair cells caused by endolymph vs. perilymph?
- 150 with respect to endolymph
- 70 with respect to perilymph
What is place principle?
nervous system detects sound frequencies by determining positions along the basilar membrane that are most stimulated
Where is the primary auditory cortex located?
Superior temporal gyrus in temporal lobe
