6.3.1 Ear Structure and Function Flashcards
What makes up the kinetic labryinth and what is the function?
- Semicircular Canals (three) and Crista Ampullaris
- Detect changes in rotational acceleration
What is the sequence by which sound wave entering the ear result in 8th nerve activity?
What are the peripheral components of the auditory system?
-external, middle, and inner ear
What is the role of the vestibular system in regards to balance and movement?
- Hair cells provide info about motion and gravity from the left and right sides
- Brain compares the info from the two sides
- Information does not reach the cortex, but does interact with the motor system
- Other systems also provide info about position: Visual system and Proprioception (somatosensory)
What are the 3 components of the cochlea?
- Inner: Scala Media filled with endolymph
- Outers: Scala Vestibuli and Scala Tympani filled with perilymph
Both auditory and vestibular hair cells transduce energy via?
movement of their stereocilia
What are the transducers for both the auditory and vestibular system?
Hair cells
What is pressure equalization in regards to middle ear functions?
- Eustachian tube connects the middle ear and the nasopharynx
- Tensor veli palatini and salpingopharyngeous muscles open the Eustacian tube during swallow
Describe the movement of the basilar membrane, is it uniform throughout?
What is the role of the basilar membrane and how do hair cells affect this?
- Basilar membrane: floppy membrane receiving different frequencies at specific regions
- Hair cells sit atop of the basilar membrane within the scala media endolymph
- Tectorial membrane sits atop of the stereocilia of the hair cells
- As hair cells move, a shearing force is produced relative to the tectorial membrane
- Causes changes in AP firing rate
What is the importance of the middle ear?
-filled with air; ossicles conduct vibrations from tympanic membrane to the oval window of the cochlea
What is the mechanism by which the saccule and utricle detect changes in linear acceleration (gravity)?
- Stereocilia embedded in gelatinous glycoprotein matrix filled with otoliths
- Otoliths (calcium carbonate crytsals) shift during linear acceleration
- Results in bending of stereocilia
Damage to auditory or vestibular nerve results in?
Hearing loss or balance disorders
What is the importance of the inner ear?
-filled with fluid; where mechanical sound vibration or motion is transduced into neural activity
What is the function of the auditory system how is this achieved?
provides information about sound in the environment
- Afferent info from CN VIII synapses on cochlear nuclei in brainstem
- Auditory information reaches the cortex
How does the cochlea allow for transmission of sound?
- Entry: from stapedal vibrations at oval window through scala vestibuli
- Exit: at round window through scala tympani
What is the mechanism by which the ampullae (semicircular canals) detech angular acceleration?
- Hair cells are located in ampullae on a ridge of tissue called the crista ampullaris
- Stereocilia are embedded in the cupula, a tall glycoprotein matrix mass
- Cupula is deflected by fluid flowing through the canal when the head turns
- Results in bending of stereocilia
Stereocilia have what at their tips and what is this importance?
- Stereocilia have potassium channels at their tips
- Bending causes either opening/closing of channels, influx of K+ causes opening of Ca++ channels, changing amount of NT released
- Results in a change of AP frequency
Describe the ionic composition of the endolymph vs the perilymph.
- Endolymph: low Na, Cl; High K
- Perilypmh: high Na, Cl; Low K
The basilar membrane location that experiences the greatest displacement depends on?
Mechanical properties of the membrane and frequency of sound
What are the characteristics of the Macular organs?
- Saccule and Utricle
- Detect changes in linear acceleration (gravity)
What is the Stria Vascularis?
lining of the scala media, secretes K+ ions to maintain potential
What is the importance of the external ear?
-amplifies sound reaching the tympanic membrane
What is the function of the vestibular system how is this achieved?
- provides information about motion and gravity
- Afferent info from CN VIII synapses on vestibular nuclei in brainstem
- Information does NOT reach the cortex
What are the properties of the inner hair cells of the cochlea?
- Primarily responsible for sending info to the CNS via CN VIII afferents
- Organized in a single row
- Sensory transducers
- Single CN VIII afferent contacts a single inner hair cell; one IHC receives several contacts
Hair cells within the cochlea sit on what?
They sit in a specific orientation on a structure called the basilar membrane.
Describe the central auditory pathway.
What are the peripheral components of the vestibular system?
Inner ear
Shearing force against stereocilia with basilar membrane movement does what?
change in hair cell membrane potential causes release of neurotransmitter at the base.
What are the characteristics of outer hair cells?
-Change the stiffness of the basilar membrane
-Damage changes thresholds and
- Organized in three rows
- Modulate sensory transduction by IHCs
- Synapse with efferent fibers from the brain
- Originating in superior olivary nucleus
- Amplify the transduction of quiet sounds and attenuate the transduction of loud sounds
- Can create otoacoustic emissions
Describe the wave displacement of the basilar membrane at the base and apex. Relate this to stiffness and frequency.
- Wave produced by stapes at oval window moves from base to apex of the basilar membrane
- Stiffness of the membrane differs along its length
- -Base: narrow and stiff
- -Apex: wide and flexible
-Amplitude of displacement at a given location of the membrane depends on the frequncy
- -Base: high frequencies (stiff membrane ⇒ requires more energy to displace)
- -Apex: low frequencies (flexible membrane ⇒ requires less energy to displace)
How do the basilar membrane and cochlea act in tonotopic organization?
How does the middle ear gain control of vibrations reaching the inner ear?
- Tensor tympani and stapedius muscles can change the stiffness of the tympanic membrane
- Used to dampen the movement of the stapes
- Increases the dynamic range of the inner ear and protects cochlear hair cells from loudness
What are the two membranes of the cochlea?
- Vestibular: separates scala vestibuli from scala media
- Basilar: separates scala media from scala tympani
Describe the membrance potentials between the endolymph and the hair cell membrane and what the importance of this is.
- Endolymph: +80mV
- Hair Cell Membrane: -40mV
- 120mV membrane potential difference drives K+ ions from the endolymph into the hair cells
How is sound information organized in the auditory system?
Auditory - frequency
What is impedence matching in regards to middle ear functions?
-Ossicular chain and the size difference between the tympanic membrane and oval window prevent loss of pressure at the oval window
Outer hair cells are innervated by?
What does the cochlea do?
Produces nerve impulses in response to sound and vibration
What are the two types of organs in the vestibular system?
Static Labyrinth (macular organs)
Kinetic Labyrinth
How does hair cell bending in regards to kinocilium alter the function of nerve conduction?
- Deflection of hair bundle toward kinocilium (tall side): depolarization and excitation
- Deflection of hair bundle away from kinocilium (tall side): hyperpolarization and inhibition
