Chapter 52 Flashcards
What are the 3 tubes in the cochlea?
o Scala vestibuli
o Scala media
o Scala tympani
Which tube contains the organ of corti?
scala media
What is the membrane called that separates the scala vestibuli and media?
Reissner’s/vestibular membrane
What is inside of the organ of corti?
hair cells
The basilar membrane separates which 2 tubes?
scala media and scala tympani
High frequencies are best heard at which portion of the basilar membrane?
close to the oval window
Medium frequencies are best heard at which portion of the basilar membrane?
middle of the basilar membrane
Low frequencies are best heard at which portion of the basilar membrane?
at the apex of the membrane
The nerve fibers from the hair cells lead to which ganglion?
spiral ganglion
the spiral ganglion has fibers that make up which nerve?
cochlear nerve
What are the stereocilia on the hair cells?
project upward from hair cells and are embedded in the tectorial membrane, which is in the scala media. Bending of the hair cells in 1 direction depolarizes the hair cells, and bending in the opposite direction hyperpolarizes them. This excites the auditory nerve fibers synapsing with their bases
The outer ends of the ahir cells are fixed in a flat plate, which is called what?
reticular lamina
True or false: the basilar fibers, rods of Corti, and reticular lamina move as a rigid unit.
True
What does upward movement of the basilar fiber do to the reticular lamina?
rocks the reticular lamina upward and inward toward the modiolus
What does downward movement of the basilar fiber do to the reticular lamina?
, the reticular lamina rocks downward and outward
The thin filaments that attach the tips of the stereocilia cause what when the cilia are bent toward the scala vestibuli?
it opens K channels –> depolarization of the hair cell
What is the place principle?
the major method used to determine different sound frequencies (typically higher pitched) by determining the positions along the basilar membrane that are most stimulated.
What is the volley/frequency principle?
low freq sounds can cause volleys of nerve impulses synchronized at the same frequencies, and these volleys are transmitted by the cochlear nerve to the cochlear nuclei of the brain.
What is the range (Hz) of human hearing?
20-20,000 Hz
In old age, what can a person typically hear?
50-8,000 Hz
After nerve fibers from the spiral ganglion of Corti enter the dorsal and ventral cochlear nuclei, where do they synapse?
onto 2nd order neruons, and decussate to other side (some stay on same side) to SOC
From the SOC, how do the auditory fibers get to the thalamus?
SOC –> lateral lemniscus –> inferior colliculis –> medial geniculate nucleus
From the MGB, how do the neurons get to the auditory Cx?
auditory radiations
Where is the auditory Cx?
lies of the supratemporal plane of the superior temporal gyrus and extends to the lateral side of the temporal lobe + much of the insular cortex + some of the lateral portion of the parietal operculum
What are the 2 parts of the auditory Cx?
1o auditory cortex (A1), and the auditory association cortex
How many tonotopic maps are there in A1?
6
Where are the low and high freq sounds heard for the tonotopic maps of A1?
Low frequencies are heard anteriorly, where high are posteriorly
What happen if we removed the auditory cortex from a cat or monkey? Would they be able to still hear?
They would still be able to hear. However, it would greatly reduce the animal’s ability to discriminate different sound pitches and especially patterns of sound. Patterns meaning a sequential series of sounds one after another.
What would happen if you have a lesion at the auditory association areas but not the primary Cx?
you can still hear and differentiate simple sound patterns. However, you can’t interpret the meaning of sound.
What are the 2 mechanisms for determining the direction of sound?
- The time lag between the entry of the sound into 1 ear and its entry into the opposite ear
- Difference between the intensities of the sounds in the 2 ears.
Direction of sound via time lag is best for what frequencies?
below 300 Hz
Is time lag better or worse than intensity for determining direction? Why?
discriminates direction much more exactly than intensity because it does not depend on extraneous factors.
Direction of sound via intensities is best for what frequencies?
higher frequencies because the head is a greater sound barrier at these frequencies
How can you differentiate sounds coming in front of vs behind or above vs below?
by pinnae of the 2 ears: the shape of the pinna changes the quality of the sound entering the ear, depending of the direction where the sound comes from.
Neuronal analysis for direction of sound begins at which structure?
SOC
The SOC is divided into what 2 parts?
Medial and lateral superior olivary nuclei
What does the lateral SOC recognize to determine direction for sounds?
by comparing the difference in intensities of the sound reaching the 2 ears. They then send appropriate signals to the auditory Cx to estimate the direction.
What does the medial SOC recognize to determine direction for sounds?
detects the time lag between the signals from the 2 ears.
How does the medial SOC recognize time lag? Give me the mechanism.
. It has a large # of neurons that have 2 major dendrites, 1 projecting to the right and 1 to the left. The sounds from the right ear impinge on the right dendrite, and the sounds from the left ear come signal the left dendrite. The intensity of excitation of each neuron is highly sensitive to a time lag. Some neurons respond maximally to a short time lag, and some respond maximally to a long time. Therefore we make up a spatial time pattern in the medial superior olivary nucleus, which can then tell the auditory cortex where the sound direction is coming from
What is otosclerosis?
fibrosis of the middle ear following repeated infection or hereditary factors. Sound waves cannot be transmitted easily through the ossicles from the tympanic membrane to the oval window.
