Physiology of the Auditory and Vestibular Systems (Pierce) Flashcards
Displacement along what results in our ability to hear sound
Basilar membrane
Basilar membrane
Narrow and stiff where?
What frequency of sounds does this region receive?
Near the oval/round windows
High frequency (bird singing or whistling)
Basilar membrane
Wider and more flexible where?
What frequency of sounds does this region receive?
Near the helicotrema/apex
Low frequency sound (Thunder or Tuba)
What kind of receptors are ear hair cells
They are mechanoreceptors. They convert mechanical signal to electrical signal
They receive afferent and efferent input, but are themselves not neuronal
What are the characteristics of the ear hair cells
- Polarized epithelial cells
- Have a basal and apical end
- Stereocilia exist on apical surface
- Stiff, graded in size and rich in actin
- Neural synapses on basal side
Endolymph
- Produced by Stria Vascularis
- Found in Scala Media
- Potassium Rich fluid that bathes the apical end of the hair cells
Perilymph
- Found in Scala vestibuli and scala tympani
- Potassium Poor fluid that bathes the Basal end of the cochlear hair cells
How do the hair cells convert mechanical signal to an electrical signal
- Sound causes deflection of the stereocilia that opens mechanically gated K+ channels, which allows K+ to enter the cell, depolarizing it.
- Change in membrane voltage opens TRPA1 channels, allowing Ca2+ to flow in, further depolarizing the cell and causing release of NTs glutamate and generation of an AP in CN VIII
NOT: K+ enters cells because stereocilia are bathed in endolymph
Deflection of streocilia towards the long end result in what
Depolarization
Deflection of streocilia towards the short end result in what
Hyperpolarization
Because K+ channels close so K+can’t enter cell
What is the Stria Vascularis
Highly vascularised area on the lateral wall of the Scala media (cochlear duct) that maintains the electrochemical properties of the endolymph by producing high levels of K+ into the endolymph
Blood labyrinth barrier (BLB)
formed by the stria vasculais. One of the main sites of drug entry to access the inner hair cells, sometimes to its detriment.
What is a common source of otoxic drug secretion into the cochlea
Stria vascularis (corsses BLB)
What can diminish the endocochlear potential
Any substance (medication, drugs, carbon monoxide, etc.) that disrupts the function of the stria vascularis. This will impact hearing.
What is the primary source of auditory information
Inner hair cells
What are the primary cells that amplify sound waves and how do they do this?
Outer hair cells
They are contractile cells. Their contractile properties boosts the mechanical vibrations of the basilar membrane
What is the arrangement of inner and outer hair cells
Inner: single layer
Outer: three rows
What do inner and outer hair cells synapse with
Inner: peripheral terminal of primary afferent neurons & efferent neurons
Outer: peripheral terminals of afferent neuroms from the spiral ganglion & efferent neurons
Impulses produced by the ear itself originate where and what are the sounds called
Superior olivary complex
olivocochlear efferents
Medial olivary complex neurons innervate ____ hair cells
Lateral olivary complex neurons innervate ____ hair cells
- Outer
- Inner