Auditory System 1: Structure & Function of the Middle & Inner Ear Flashcards
The auditory system is designed to transform _________ into ________ activity and ultimately to ______________ that are transmitted to the ______ to provide us with what we call hearing
- acoustic information
- mechanical
- electrochemical signals
- brain
The auditory system is divided into sections:
- outer ear
- middle ear
- inner ear
- auditory nerve
- central auditory pathways
Outer Ear Structures:
- pinna
- external auditory meatus (canal)
Middle Ear Structures:
- tympanic membrane
- tympanic cavity
- ossicular chain
- with all associated muscles, ligaments, and tendons
- Eustacian tube
Inner Ear Structures:
- oval window
- cochlea
- vestibular structures
Describe the Pinna:
- Skin-covered cartilaginous structure
- Channels sound waves into ear canal
- Pits, tags, or other malformations of the pinna indicate issues with ear development that may affect hearing
Describe the Ear Canal (External Auditory Meatus):
- From concha to eardrum
- Outer third is cartilaginous
- Inner two-thirds is bony
- The skin of the cartilaginous portion is thick and contains wax and oil glands:
- lubricate the canal
- protect the ear from foreign objects and debris
- Deep ear canal stimulation can cause referred sensation to vagus nerve making people cough
What function do the pinna and ear canal both share?
provide a boost in high frequency sound intensity
The handle of the malleus is directly attached to the _____________, which vibrates in response to ________________ funneled in by the external ear
- tympanic membrane
- sound pressure waves
- The malleus is attached to the ______, which is attached to the ______.
- The footplate of the stapes directly contacts the ________ on the inner ear.
- incus; stapes
- oval window
How do ossicles of the middle ear amplify sound vibration?
- lever mechanism
- area difference between the tympanic membrane & the footplate of the stapes
- This increases the force per unit area of the vibrations of the footplate of the stapes on the oval window of the inner ear
Describe the protective feedback mechanism for loud sounds:
- dampens the vibration of the ossicles
- activation of two muscles:
-
tensor tympani
- attached to the handle of the malleus
-
stapedius muscle
- attached to the neck of the stapes
-
tensor tympani
- When these muscles contract, vibration of these ossicles are reduced
- tensor typani = trigeminal nerve
- stapedius muscle = facial nerve
What are the functions of the inner ear?
- hearing
- balance
The inner ear is contained in the __________ of the temporal bone, and is encased in a bony structure called the ____________.
- petrous apex
- osseous or bony labyrinth
Labyrinth:
3 Sections
- vestibule
- cochlea
- semicircular canals
Desrcibe communication in the inner ear:
-
initial point of communication:
- at the oval window of the vestibule where the stapes footplate abuts the oval window membrane.
- Basal end of the cochlea:
- round window membrane
- which communicates with the middle ear space
What is the modiolus?
- core of the cochlea
- highly porous bone
- allows passage of auditory nerve fibers as they travel from the internal auditory meatus to the hair cell synapse
What is the osseous spiral lamina?
- extends from the modiolus
- coils around the center of the cochlea
- provides partial division of the upper and lower cochlear chambers:
- scala vestibuli
- scala tympani
- point of attachment for the basilar membrane
- which encases the scala media
The scala media bordered superiorly by ____________ and inferiorly by the ____________.
- Reissner’s membrane
- basilar membrane
What can be found within the membranous labyrinth?
- sensory organ of hearing: organ of Corti
- lateral wall: stria vascularis
Stria vascularis:
highly vascular tissue that is responsible for the metabolic environment of the scala media
What does the organ of Corti consist of?
- 1 row of inner hair cells
- 3 rows of outer hair cells
- Cell bodies are surrounded by supporting cells
Two Fluid Systems:
- Perilymph
- Endolymph
Where is the perilymph found?
In the scala vestibuli and scala tympani:
- High [Na+]
- Low [K+]
Where is the endolymph found?
Within the scala media:
- Low [Na+]
- High [K+]
What does the stria vascularis do?
Maintains the ionic concentrations of the endolymph
Hair cells are contacted by dendrites from what type of neurons?
afferent bipolar neurons
Many afferent fibers synapse on the same __________, while single afferent fibers branch to synapse with several ________
- inner hair cell
- outer hair cells
Efferent fibers have cell bodies in the ________________ of the brainstem and synapse directly on __________ and on the afferent fibers of ___________
- superior olivary complex
- outer hair cells
- inner hair cells
Inner and outer hair cells transduce __________movement into an _________ signal to stimulate the __________.
- mechanical
- electrochemical
- auditory nerve
What do the motile properties of the outer hair cells result in?
- increased basilar membrane motion
- responsible for the cochlear amplifier
Stereocilia:
- project through the reticular lamina
- stiff hair-like structures that deflect with mechanical disturbances
- connected to each other by filamentous cross-links and tip-links
- move as a unit to ensure connection
How is the base of the cochlea different compared to the base of the apex?
- start of tonotopic organization
At the base:
- the basilar membrane is narrow and
stiff - where high frequencies are detected
At the apex:
- basilar membrane is wide and floppy
- where low frequencies are detected
Describe the “traveling wave”:
-
pressure waves:
- transmitted from **middle ear ⇒ cochlea **
-
cochlear fluid is displaced:
- causes wave-like motion along the length of the basilar membrane
Hair cell function and synaptic stimulation:
- Movement of the endolymph produces deflection of the stereocilia
- Deflection of the stereocilia (in one direction) opens ion channels of stereocilia
- Positive ions flow inward, through open channels, depolarizing the hair cell
- Depolarization causes neurotransmitter release, stimulating the auditory nerve fibers.
What are the 2 types of hearing loss? How are they diagnosed?
- Conductive Hearing Loss
- Occlusion or dysfunction of the external and/or middle ear
- Sensorineural Hearing Loss:
- Dysfunction of the cochlea and/or auditory nerve
- By comparing the threshold for detection of an airborne stimulus compared to a
matched stimulus to the temporal bone, the audiologist can distinguish hearing
defects that originate in different parts of the ear
