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sound waves consist of:
Alternate Regions of Compression & Rarefaction of Air Molecules
neural perception of sound energy involves what 2 aspects:
–Identification of the sounds (“what”)–Localization of the sounds (“where”)
what are sound waves?
- Traveling vibrations of air
- Consist of alternate regions of compression and rarefaction of air molecules
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
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
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
the middle ear bones convert:
the vibrations of the tympanic membrane into fluid movements in the inner ear
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
the inner ear house what 2 different sensory systems:
what do they do?
- »Contains receptors for conversion of sound waves into nerve impulses which makes hearing possible
- Vestibular apparatus
- »Necessary for sense of equilibrium
type of system:
- 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
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
the scala vestibule (upper) is sealed from the:
middle ear cavity by the oval window
the scala tympani is sealed from the:
middle ear by the round window
the vestibular membrane forms the:
top of the scala media, separating it from the scala vestibuli
the basilar membrane forms the:
floor of the scala media, separating it from the scala tympani
which membrane has the Organ of Corti?
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
Organ of Corti converts:
fluid movement into neural signals
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
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?
- 1.Displacement of the round window (this is the imp one)
- 2.Deflection of the basilar membrane
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
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.
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
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
- 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.
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
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.
how does each semi-circular canal lie in relation towards one another?
- at right angles to each other
- in 3 different planes
The enlarged base of each semicircular canal is called
The receptor hair cells of each semicircular canal are located:
on a ridge in the ampulla.
The hairs are embedded in:
the cupula, a gelatinous layer. This is the fluid layer.
The cupula sways in the direction of:
when you move your head, what happens to the endolymph?
it lags behind bc of inertia
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
the cells of the vestibular hair cell consist of:
One kinocilium and a tuft of stereocilia, arranged in rows of decreasing height
where are the utricle and saccule Located?
between the semicircular canals & the cochlea
what makes the layer heavier?
he Tiny crystals of calcium carbonate that are suspended within the gelatinous fluid.
what is the position of the hairs when a person is upright?
- the utricle hairs are vertical &
- the saccule hairs are oriented horizontally
Neural signals generated in response to:
mechanical deformation of hair cells by specific movement of fluid and related structures
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