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sound waves consist of:
Alternate Regions of Compression & Rarefaction of Air Molecules
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neural perception of sound energy involves what 2 aspects:
–Identification of the sounds (“what”)–Localization of the sounds (“where”)
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what are sound waves?
- Traveling vibrations of air
- Consist of alternate regions of compression and rarefaction of air molecules
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3 qualities of hearing:
- 1. Pitch (tone) of sound
- –Depends on frequency of air waves
- –Higher pitch corresponds to greater frequency of vibration
- 2. Intensity (loudness)
- –Depends on amplitude of air waves–Measured in decibels
- Timbre (quality)
- –Determined by overtones, additional frequencies superimposed on the pitch
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what are the external ear components:
- Pinna: collects sound waves and channels them down the ear cana
- lThere are glands that produce cerumen (ear wax) lining the canal.
- Ear wax, along with fine hairs at the entrance to the canal, are protective mechanisms
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describe the sound wave transmission of the TM?
The tympanic membrane vibrates when struck by sound waves
Alternating high & low pressures of the sound wave cause the tympanic membrane to bow inward & outward in sync with the frequency of the wave
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the middle ear bones convert:
the vibrations of the tympanic membrane into fluid movements in the inner ear
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sound wave transmission:
- middle ear transfers vibrations thru ossicles
- waves in cochlear fluid set basilar membrane in motion
- receptive hair cells are bent as basilar membrane is deflected up and down
- mechanical deformation of specific hair cells is transduced into neural signals that are transmitted to auditory cortex in temporal lobe of brain for sound perception
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the inner ear house what 2 different sensory systems:
what do they do?
- Cochlea
- »Contains receptors for conversion of sound waves into nerve impulses which makes hearing possible
- Vestibular apparatus
- »Necessary for sense of equilibrium
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cochlea-
shape:
contains:
type of system:
divided into:
- Pea-sized & snail shaped
- Contains the organ of Corti
- A coiled tubular system
- Divided into 3 fluid-filled longitudinal compartments:
- 1.Upper compartment is the scala vestibuli, follows inner contours of the coil
- 2.Middle compartment is the scala media (also called cochlear duct)
- 3.Lower compartment is the scala tympani, follows the outer contours
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what are the fluids in the cochlea?
- Perilymph: Fluid in the scala vestibuli and scala tympani
- The scala media has endolymph
- The fluid at the tip of the cochlear duct come together at the region of the helicotrema
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the scala vestibule (upper) is sealed from the:
middle ear cavity by the oval window
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the scala tympani is sealed from the:
middle ear by the round window
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the vestibular membrane forms the:
top of the scala media, separating it from the scala vestibuli
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the basilar membrane forms the:
floor of the scala media, separating it from the scala tympani
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which membrane has the Organ of Corti?
Basilar membrane
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the organ of Corti contains:
approx. 100 stereocilia project from each:
Hair calls are the:
- the auditory hair cells, which are the receptors for sound
- auditory hair cell
- mechanoreceptors
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Organ of Corti converts:
fluid movement into neural signals
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how are the hair cells arranged in the organ of Corti?
the stereocilia contact the:
- Arranged in 4 parallel rows along the length of the basilar membrane
- the tectorial membrane, an awning type of membrane extending over the length of the Organ of Corti
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the stapes hits the oval window and transmits vibrations.
the oval window bulges _______
Pressure is dissipated via what 2 pathways:
and which pathway is more imp?
- inward
- 1.Displacement of the round window (this is the imp one)
- 2.Deflection of the basilar membrane
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describe the different regions of the basilar membrane vibrating at different frequencies:
- the narrow, stiff end of the basilar membrane nearest the oval window vibrates best with high-frequency pitches
- the wide, stiff end of the basilar membrane near the helicotrema vibrates best with low-frequency pitches
- Each region of the basilar membrane is linked to a specific region of the primary auditory cortex
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what is the role of the inner and outer hair cells:
- Inner cells transform the vibrations into action potentials, sending sensory information to the CNS
- The outer cells change length in response to changes in membrane potential (Electromotility). Enhances the response of the inner hair cells.
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steps in hearing:
- 1.Sound waves enter external auditory meatus
- 2. Eardrum vibrates
- 3. Auditory ossicles (malleus, incus,stapes) amplify vibrations
- 4. Stapes hits oval window and transmits vibrations to cochlea
- 5. Organs of corti
- contain receptor cells (hair cells) that deform from vibrations
- 6. Impulses sent to the auditorynerve
- 7. Auditory cortex of the temporal lobe interprets sensory impulses
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what is the pathway for sound transduction?
- 1. sound waves
- 2. vibration of tympanic membrane
- 3. vibration of middle ear
- 4. vibration of oval window
- 5. fluid movement within the cochlea -- (OR--> vibration of round window --> dissipation of energy (no sound perception))
- 6. vibration of basilar membrane
- 7. bending of hairs of inner receptor hair cells of organ of corti as basilar membrane movement displaces these hairs in relation to the overlying tectorial membrane which the hairs contact
- 8. grades potential changes (receptor potential) in receptor cells
- 9. changes in rate of action potentials generated in auditory nerve
- 10. propagation of AP to auditory cortex in temporal lobe of brain for sound perception
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cochlear implants:
- stimulate the nerve directly
- A cochlear implant receives sound from the outside environment, processes it, and sends small electric currents near the auditory nerve.
- These electric currents activate the nerve, which then sends a signal to the brain.
- The brain learns to recognize this signal and the person experiences this as "hearing".
- The cochlear implant somewhat simulates natural hearing, where sound creates an electric current that stimulates the auditory nerve.
- The result is not the same as normal hearing.
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what re the 2 parts of the vestibular apparatus?
- Semicircular canals
- –Detect rotational acceleration or deceleration in any direction
- Utricle and saccule (the otolith organs
- -Detect changes in rate of linear movement in any direction
- –Provide information important for determining head position in relation to gravity
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function of the semi circular canals:
Detect rotational or angular acceleration or deceleration of the head. They do not respond when head is motionless or moving at a constant speed.
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how does each semi-circular canal lie in relation towards one another?
- at right angles to each other
- in 3 different planes
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The enlarged base of each semicircular canal is called
an ampula
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The receptor hair cells of each semicircular canal are located:
on a ridge in the ampulla.
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The hairs are embedded in:
the cupula, a gelatinous layer. This is the fluid layer.
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The cupula sways in the direction of:
fluid movement
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when you move your head, what happens to the endolymph?
it lags behind bc of inertia
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what happens when fluid is left behind?
what does this cause?
- the fluid in the same plane as the head movement is in effect shifted in the opposite direction from the movement.
- This causes the cupula to lean in the opposite direction of the head movement.
- The sensory hairs in the cupula also move in the direction opposite head movement.
- The endolymph will catch up if head movement continues at the same rate & in the same direction
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the cells of the vestibular hair cell consist of:
One kinocilium and a tuft of stereocilia, arranged in rows of decreasing height
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where are the utricle and saccule Located?
between the semicircular canals & the cochlea
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what makes the layer heavier?
he Tiny crystals of calcium carbonate that are suspended within the gelatinous fluid.
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what is the position of the hairs when a person is upright?
- the utricle hairs are vertical &
- the saccule hairs are oriented horizontally
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Neural signals generated in response to:
mechanical deformation of hair cells by specific movement of fluid and related structures
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Vestibular input goes to:
vestibular nuclei in brain stem and to cerebellum for use in maintaining balance and posture, controlling eye movement, perceiving motion and orientation
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