What is the pathway of auditory conduction?
- tympanic membrane
- oval window
What two muscles contribute to the attenuation reflex?
- tensor tympani muscle: pulls tension medially on the TM
- stapedius muscle: pulls the stapes laterally
- provides rigidity to the system
What is the function of the attenuation reflex?
- protects cochlea from overly loud sound
- masks low frequency sounds
- decreases person's hearing sensitivity to their own voice
What is impedance matching?
- The movement distance of the stapes is reduced, while the force of movement is increased
- it is increased by moving from a high surface area to a smaller surface area, and is required to do so as we are moving from air to a liquid substance which requires more inertia/vibrations
What is responsible for impedance matching and what is the effect if this is lost?
- the TM and auditory ossicles
- sensitivity to hearing is reduced by15-20 decibels
Which of the basilar fibers activate in response to high and low frequency and where are they located?
- short, thick fibers respond to high frequency and are located near the oval window
- long, thin fibers respond to low frequency and are located farther away from the oval window
How do hair cells stimulate nerve fibers that lead to spiral ganglion of corti?
- the stereocilia of the hair cell is embedded into the overlying tectorial membrane
- when the hair cells are bent it causes hyperpolarization or depolarization
Explain how the hair cells in the organ of corti are stimulated.
- the reticular lamina that contains the hair cells, is in a rigid attachment to the rods of corti connecting the reticular lamina and the basilar fiber
- the basilar fiber is connected to the modiolus
- the reticular lamina is able to move with a shearing force, while the basilar fibers can move with a penetrative force
- the combination of these two directoinal planes based on movement of the modiolus cause stimulation of the hair cells
What is the neurological connection of the organ of corti to the brain?
- hairs cell fibers lead to spiral ganglion of corti
- to the cochlear nerve CN8
- CN8 moves into the medulla
Where is the endocochlear potential and what is it?
- scala media is positively charged while the outside is negative
What is the importance of the endocochlear potential?
- causes the hair cells to be in a negative intracellular potential and the upper surfaces are -150 being in the endolymph
- this sensitizes the cells to respond to slightest sound
What is place principle?
- How the nervous system detect frequencies by determining positions along basilar membrane based on level of stimulation
What is the auditory stimulus pathway?
- spiral organ of corti
- CN 8
- dorsal/ventral cochlear nuclei in medulla
- synapse at superior olivary nucleus
- through the lateral lemniscus nucleus
- synapse in inferior colliculus
- synapse in medial geniculate nucleus
- end in primary auditory cortex
How is a person able to determine the direction from where a sound is coming?
- the time lag between when each ear "hears" the stimulus
- difference of intesities of the sounds
What region of the brain is responsible for detecting where sound comes from?
- lateral nuclesu by comparing differences in sound intensity
What region is responsible for detecting the time lage between acoustic signals between the two ears?
- medial superior olivary nucleus
Signals from where, directly excite the primary auditory cortex?
signals from the medial geniculate body
Signals from where excite the auditory association areas?
signals from the primary auditory cortex and from the thalamic association
In what three ways can the auditory system determine loudness?
- as loudness increase the vibrations cause an increased rate of nerve ending movement
- loudness excites more hair cells, causing spatial summation
- Outer hair cell stimulation indicates a loud sound. they require a higher threshold for activation
How does the frequency that can be heard change with age?
the range significantly decreases as we age
original range can be obtained with increased amplitude
What two chambers are considered as one chamber?
The scala media and vestibuli are separated by the thin vestibular membrane and considered one chamber
What membrane separates the scala tympani from the scala media?
Which region contains endolymph?
scala media secreted from the stria vascularis. High K, low Na
Which regions contain perilymph?
scala vestibuli and scala tympani.
could come from CSF, as this compartment is in contact with the subarachnoid space. Low in K, high in Na