Physiology of the Auditory and Vestibular Systems Dr. Pierce Flashcards
Auditory System
Detects sound to locate and identify sound source
Sound
Oscillation of air pressure
Amplitude
Sound pressure or intensity (dB)
Frequency
Number of oscillations or air pressure per second (Hz)
High Frequencies
At the base of the membrane structure of cochlea by the oval window
Low Frequency
At the Apex of the cochlea (Helicotrema) rather away from the oval window
(Wider and for flexible)
The frequency of sound is coded by
Where along the basilar membrane there is the greatest deflection
Hair Cells
Polarized epithelial cells with basal side synapsing with nerve and apical cell with actin steriocilia
Endolymph is found where
In the Cochlear Duct and Membraneous Labyrinth, Scala Media and produced by Stria Vascularis. Bathes the Apical side of hair cells where the steriocilia is
K+
Low Na+
Perilymph is found where
Scala Vestibuli and Scala Tympani, bathes the basal end of hair cells
NA+
Low K+
Deflection steriocilia causes
K+ influx
This depolarizes the hair cell which opens the CA+ channels (TRPA1) to increase more positive cations in the cell
NTS (GLUTAMATE) of hair cell is released
Hair cell at rest vs active
Hair cell at rest has a slow only continuous APs
When depolarized there is a higher frequency of many APs
Steriocilia bend away from biggest one
K+ channels close, hyperlpolarization, Ca+ does not enter since TRPA1 closes
Stria Vascularis
Makes Endolymph high in K+ and is highly vascular
= forms Blood-Labyrinth-Barrier where drugs can enter to access the inner hair cells
Some are detrimental due to disrupt the high potential in the endolymph of +80mV
Inner hair cells
Primary source of auditory deflection
Which goes to the audition you system
Outer Hair Cells
Arranged in 3 rows
Acts as an amplifier front the basilar membrane
Does this by contracting when activated which amplifies the basilar membrane
Olivochochlear Efferents
From the Superior Olivary Complex causing the outer hair cells to contract causing the motion in the basilar membrane causing amplification of sound——> through oval window ->tympanic membrane
(Sound that is form the inside)
Branches off the Olivochoclear efferents
Medial Olivary Complex: innervate the outer hair cells
Lateral Olivary Complex: innrevate the inner hair cells
Otoacoustic Emissions
Done to infants to test inner and middle ears
These are the sounds made form the olivoacustic efferents and this test listens to make sure emissions are there when they are evoked by pulsing sound in the ear = normal hearing
Can be spontaneous in 1/3 people
From outer hair cells in middle ear constricting
Auditory chain STEP 1: Dorsal Cochlear Nuclei and Ventral Cochlear Nuclei
Comes form the cochlea to the Medulla (DCN and VCN)
DCN= integrates acoustic information with the somatosensory information
VCN= processes the temporal and spectral features of the sound (high or low sounds)
BASIC LEVEL PROCESSING
Auditory chain STEP 2: Superior Olivary Complex
MSO
LSO
Form the medulla ——-> (GLUTAMATE) excitatory comes to the SON
Info from both ears converge here = TO LOCALIZE SOUND
Medial SON (MSO): generates map of TIME DIFFERENCE between the two ears hearing to find location of the sound
Lateral SON (LSO): generates map of INTENSITY DIFFERENCE between the two ears to find location of the sound
Auditory chain STEP 3: Inferior Colliculus
Suppresses echo sounds ,
Which interfere with finding location of sound
adds TIME + INTENSITY difference
=find the final localization of sound
Auditory chain STEP 4: The Medial Geniculate Nucleus
Relay station of auditory info to cortex
Many conversions of spectral (intensity) and temporal (time) pathways = allows us to process speech inflections when someone talks
Auditory chain STEP 5: Primary Auditory Cortex
IS TONOTOPIC
Conscious perception of sound (begin to interpret sound)
Higher order processing of sound (LOUDness, Modulation of volume, frequency of modulation)
TONOTOPIC FEATURES OF PRIMARY AUDITORY CORTEX
More rostral area (anterior)= low frequency -apex of cochlea
More caudal area (posterior)= higher frequency -base of cochlea
Auditory (Secondary) Association Cortex
Broca’s and Wernicke’s area
More complex sounds responses to music undulations
Identify or name sounds, and speech
Lateral OC (LOC)
Going to inner hair cells don’t directly go to them
Other Olivochoclear Efferents in protecting the ear
=Can freeze the outer hair cells from contracting to dampen the sound and make sure the basilar membrane doesn’t move
=Also decreases inner hair cells from responses
Middle Ear Efferents in protecting the ear
Motor innervation to the tensor tympani to (malleus, and Tympanic Membrane) and to the Stapedius to (Stapes)
= tensing and contracting the muscles to keep the malleus and stapes to not move
= work at low frequency to improve hearing them: to help with speech discrimination
= work at high frequency: to protect the hair cells
Tinnitus
Constant Ringing in the ear
Due to Middle Ear Efferents being damaged
Autonomics to protect the ear
Innervation to ear can come from
1. CN 8
2. Caroticotympanic Nerve form the Superiro Cervical Ganglion——> mucus glands of the tympanum and the Ear drum BVs and components
3, Acoustic Nerve (Sympathetic)——> BVs in cochlea
Make sure blood in flowing to the parts of the ears, can be maintained of increased by OMM
Sensorineural Hearing Loss
Form noise, toxins, age, or unknown
Due to Damage to hair cells, or nerve fibers
(MOST COMMON FOR OUTER HAIR CELLS, of the BASE of COCHLEA)
1. Damage to outer hair: decreased sensitivity to sound (broader tuning)
2. Damage to the inner hair: to sound input to the CNS
Cochlear prosthesis= can restore some hearing
Cochlear Prosthesis
An electrode wire is placed through the cochlea and gets stimulated by the frequencies it should stimulate the basilar membrane with and signals surviving hair cells by bypassing damaged areas
Anterior Semicircular Canal
Rotation of vertical axis forward
Falling forward
Horizontal Semicircular Canal
Rotation on horizontal plane like spinning in circle
Posterior Semicircular Canal
Rotation of vertical axes backwards
Falling backwards
Utricle
Linear acceleration forwards and back
Running forwards or backwards
Saccule
Linear Acceleration up and down
Jumping up to dunk a basketball
