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The Ear: PhysiologyBalance and Hearing
MechanoreceptorsCan respond to deformation
(bending), resulting in a change in ion flow
Get a hyper/depolarization depending on the direction◦Can differentiate between direction of
bendingOften grouped Often attached to a gelatinous mass,
which is influenced by the environment’s movement
Inner Ear Anatomy
Semicircular canalsSurrounded by both a membranous
labyrinth and a bony labyrinth◦Can’t expand/change shape◦Held still even when body is in motion◦Movement of fluid causes a traveling disturbance whose force isn’t lost against an expanding wall
Tubular structure that contains both perilymph and endolymph
Each canal ends with an ampulla
Cristae ampullarisContain “tufts” of hair cells,
called cristaeAffected by movementAre in planes perpendicular to
one another (able to interpret any possible movement)cupola
Vestibular ApparatusEnlargements extend from
the vestibular apparatus◦Utriculus and sacculus
Gelatinous mass with CaCO3 “ear stones” = cupola
This extra mass helps increase density◦A more efficient position receptor◦Allows proprioceptors a reference
point to which it can compare the rest of the body
Endolymph is continuous throughout the vestibular apparatus and semicircular canals
During rotation of canals◦Inertia moves the walls relative to the
fluid◦Fluid gains inertia of its own◦When the wall stops, fluid moves relative
to the wallEndoloymph is also continuous
throughout the cochlea
The Cochlea
Cochlea – A Hearing Structure1 central canal, filled with
endolymph2 adjacent canals, filled with
perilymphThis fluid allows vibration of the
walls of the central canal
Vibration TransmissionTympanic membrane vibrates
along with sound waves Translated into the motion of
the bones of the inner ear Stapes attached to the oval
window The oval window vibrates at the
same frequency
Vibration of oval window causes disturbance in the fluid behind it◦High surface area leads to an amplification of the sound
◦The pressure on the perilymph in the vestibular canal is great, causing pressure waves
Round window acts as a pressure release
Sound detection
Vibrations produced in the perilymph are translated into traveling waves along the basilar membrane◦Frequency of the vibration determines how
far it goes◦High = proximal membrane◦Low = distal end
A maximal response happens along the portion of the membrane that vibrates the most
Hearing in detail…2 groups of hair cells along
basilar membrane◦Single, inner row (closest to bony
ridge)◦Vibrate with basilar membrane◦Communicate with auditory cortex of
brain via a single nerve fiber in auditory nerve
Why does this matter?Your brain can “tell” what type of
sound was perceived◦A fairly strong stimulation needed to
stimulate the hair cells so close to the bony ridge
◦If this nerve fiber is stimulated, the sound must be loud
Outer, Triple RowSensitive to the same frequency as
the inner, single rowEasier to stimulate, thoughBrain can’t distinguish the specific
frequency that stimulates these cells, though
Harder to identify quieter soundsTurning up volume helps!