Auditory Physiology Flashcards
What is sound?
Oscillations of air pressure
What is amplitude?
Sound pressure (intensity) measured in Decibels
What is frequency?
Number of oscillations of air pressure per second measured in Hz
Describe the properties of the basilar membrane?
It is narrow and STIFF near the oval/round windows
It is wider and FLEXIBLE near the apex (helicotrema)
Motion at the base of the basilar membrane is done by?
High pitched sounds (high frequencies)
Motion at the apical end of the basilar membrane is done by?
Low frequency (pitched) sounds
The frequency of sound is coded by?
Where along the basilar membrane there is the greatest DEFLECTION
High pitched sounds deflect the basilar membrane where?
Near the round/oval windows at its base
Low pitched sounds deflect the basilar membrane where?
Near the helicotrema near its apex
What type of receptors are hair cells?
Mechanoreceptors
Are hair cells neurons?
Nope
What exists on the apical surface of hair cells?
Stereocilia
What protein is within stereociliar?
Actin
What can be found at the basal end of stereociliar?
Afferent and efferent nerve fiber synapses
Levels of potassium and sodium in Endolymph?
HIGH K and low na
Levels of potassium and sodium in Perilymph?
LOW K and high na
Does endolymph or perilymph bath the apical surface of hair cells?
Endolymph = apical end Perilymph = basal end
As the basilar membrane is deflected by sound, it moves the hair cells against the tectorial membrane. What way must the stereocilia be deflected in order to depolarize?
TOWARDS the tallest stereocilia
As the stereocilia at deflected towards the tallest one, what is opened?
Mechanically gated K+ channels and potassium enters cell
____ connects stereocilia and the force is transmitted to ______
Tip links
Elastic gating spring
Once potassium is allowed into hair cells, then what happens?
TRPA1 channels are opened and Ca++ enters the cell
What ions come into the hair cell to depolarize it and allow for NT release?
K and Ca
What neurotransmitter is released from hair cells?
Glutamate
If the stereocilia at deflected towards the smallest stereocilia, what happens?
Hyperpolarization
What produces endolymph?
Stria vascularis
Where is the stria vascularis?
In the scala media
As the stria vascularis produces endolymph (high in K+), what does this create for the scala media?
A resting membrane potential of +80 mv
The potential of +80 mv in the scala media creates what?
Drives (+) ions down their conc. gradient into hair cells and creates a blood-Labyrinth Barrier (BLB)
Any substance that crosses _____ can damage/impact hearing by hurting the stria vascularis?
BLB - blood labyrinth barrier
Inner hair cells are?
Primary source of auditory info
Inner hair cells are arranged into a ___ layer
single
Outer hair cells act as?
An amplifier of sound
Outer hair cells are arranged into ____ rows
3
What property allows the outer hair cells to amplify sound?
They are contractile epithelial cells and when they contract, it further displaces the basilar membrane!
When the ear itself produces sound it is known as?
Otoacoustic emissions (OAE)
Describe how an ear can itself produce sound?
Impulses originate at the superior olivary complex
- Olivocochlear efferents go to outer hair cells
- Outer hair cells then contract and displace the basilar membrane which produces sound that travels back out middle hear and to tympanic membrane
2 types of OAE
Spontaneous and Evoked
Evoked OAE test?
Hearing loss on infants
- Evoked emissions will NOT be present if there is hearing loss
Posterior cochlear nuclei
Integrates acoustic information with somatosensory
Anterior cochlear nuclei
Begins processing temporal and spectral features of sound
Medial superior olivary complex
Generates a map of interaural TIME differences to help localize location of sound
Lateral superior olivary complex
Generates a map of interaural INTENSITY differences
Inferior colliculus
Suppressed information related to echoes and creates a precise origin of sound location
Medial geniculate nucleus
Relays all information about sound to the primary auditory cortex
Primary auditory cortex
Conscious perception of sound
What is the arrangement of the primary auditory cortex?
Rostral regions = low freq. sound
Caudal regions = high freq. sound
What does the secondary auditory cortex respond to?
More complex sounds like music and identifying/naming a sound
The secondary auditory cortex includes?
Broca’s and Wernicke’s areas
What are the efferent innervations in the ear?
Olivocochlear, Middle ear muscle motoneurons, autonomic innervation of inner ear
What do olivocochlear efferents do?
In response to LOUD noises, they decrease basilar membrane motion and protect hair cells
What do middle ear muscle motoneurons do?
In response to LOUD noises, bilateral contraction to reduce transmission of sound and prevent damage
What are the middle ear muscles?
Tensor tympani and stapedius
What is the autonomic innervation of the inner ear comprised of?
Sympathetic adrenergic fibers
What causes Sensorineural hearing loss?
Damage to hair cells or nerve fibers or both
Which type of hair cell is more susceptible to injury?
Outer hair cells
Damage to outer hair cells?
Decrease sensitivity to sound
Damage to inner hair cells?
Cut off auditory input to CNS
How to cochlear prostheses restore some hearing?
Electrode array threaded through cochlea and stimulates surviving nerve fibers
Part of ear activated by forward motion
Anterior semi-circular canals
Part of ear activated by backward motion
Posterior semi-circular canals
Part of ear activated by rotation
Horizontal semi-circular canals
Part of ear activated by linear acceleration forward and backward
Utricle
Part of ear activated by linear acceleration up and down
Saccule
What are the main structures that are involved in the pathway of sound processing?
Cochlear nuclei Superior olivary complex Inferior colliculus Medial Geniculate nucleus Primary auditory cortex
What innervates outer hair cells?
Medial olivary complex neurons
What innervates inner hair cells?
Lateral olivary complex neurons
