4 - Grover - Auditory and Vestibular Function Flashcards
Specialized Membranes in ciliated hair cells?
Describe each
Apical - Sensory transduction zone, one kinocilium, several stereocilia
Basolateral - resting potential, synaptic transmission zone (CN VIII afferents)
Explain sensory transduction in Hair Cells
Explain depolarization, hyperpolarization, and no change
Graded receptor potential by bending cilia
Directionally sensitive:
Toward Kinocilium - depolarization (excite)
Away Kinocilium - hyperpolarization (inhibit)
Perpendicular Kinocilium - No Change
Describe the physical process of sensory transduction in hair cells
Bending of cilia pulls open mechanically gates ion channels, located in stereocilia
Stereocilium are mechanically linked
Ion Channels in Hair Cells
Cation Channels
K+/Ca2+ permeable
Bending toward opens, bending away closes
Describe the Fluid Surrounding Hair Cells and its importance in Sensory Transduction
What is the driving force?
Apical - Endolymph
High K+ / Low Na+
Basolateral - Perilymph
Low K+ / High Na+
- - -
Driving force for K+ is inward across apical membrane, outward across basolateral membrane
Consequences of driving force of cations in hair cell membranes?
Basolateral - outward (K+) force creates negative resting potential
Bending of mech-gated cation channels allows inward current flow, creates capacitive current which depolarizes basolateral membrane
Transmitter Release in Hair Cells?
Influx of K+ opens Voltage Gates Calcium Channels
Calcium influx triggers glutamate release via vessicles
NO Action Potentials in hair cells
Rates of Transmitter Release in Hair Cells?
Hair cells release glutamate at rest
Bending toward kinocilium increases rate
Bending away kinocilium decreases rate
Locations for Vestibular Hair Cells (organs)
Locations for Auditory Hair Cells (organs)
- Otolith Organs (utricle, saccule): Respond to LINEAR ACCELERATION
- Semicircular Canals (ampullae): Respond to ANGULAR ACCELERATION
- - -
Organ of Corti: Respond to SOUND PRESSURE WAVES
Otolith Organs:
Organs?
Layers/Components?
Action?
Organs: Utricle, Saccule
Layers:
Main - Macula (sensory epithelium)
Components: Vestibular Hair Cells, Support Cells, Gelatinous Layer, Fibrous outer otoconia layer (otoliths)
- - -
Otoconia are heavier than surrounding fluid, head tild changes relative direction of gravitational acceleration–shear force bends cilia
LINEAR ACCELERATION (or deceleration)
Orientation of hair cells in otolith organs?
How does this change?
Adjacent hair cells have similar organization
Orientation changes gradually across maculae, abruptly at striola
Difference in Directional Sensitivity in Otolith Organs
Utricle - Horizontal
Saccule - Sagittal
- - -
Maculae on each side are mirror images–Linear acceleration in any direction depolarizes on side, and hyperpolarizes other side
Semicircular Canals:
Ampulla
Crista
Cupula
Fluid type?
Ampula - Swelling
Crista - Sensory epithelium
Cupula - Geleatinous mass hair cells extend into
Canals are filled with endolymph
What type of motion to semicircular canals detect?
How does this process occur?
Angular Acceleration
When the body is in motion, endolymph lags begind canal–fluid has intertia
The cupula and cilia embedded in it are bent
How are Semicircular canals paired?
Each canal is paired with a second canal in the same plane
Left Horizontal + Right Horizontal
Left Anterior + Right Posterior
Left Posterior + Right Anterior
L - HAP
R - HPA
How are paired semicircular canals affected by rotation of head?
Rotation of head causes opposite changes
Hair cells in the canal towards with the head is rotating are depolarized
Hair cells in the canal opposite with the head is rotating are hyperpolarized
What occurs to Semicircular canals during constant velocity?
During a rotation to the left, what occurs?
When a rotation comes to an abrupt stop, what occurs?
They are only measuring angular acceleration, when velocity is constant, outputs adapt as endolymph begins to rotate at same velocity as head
- - -
Hair cells to the left are depolarized, afferents on left increase firing rate
Hair cells to the right are hyperpolarized, afferents on right decrease firing rate
Endolymph keeps moving (intertia), perception is rotation in opposite direction
What is the basic journey of sound in the ear?
Outer ear funnels and amplifies sound wave in air, converted to vibrations, converting sound wave in fluid, which is detected by bending of cilia
Outer Ear Functions
Loss of function?
- Amplification (10 dB)
- Localization: Vertical location
- - -
Conduction Deafness - obstruction, air conduction impaired, bone conduction normal
Can test this with tuning fork, we do this intentionally with ear plugs
Middle Ear Function:
Impedance Matching - How?
Impedance Matching - Increase of force to convert air sound waves to fluid sound waves
- Tympanic Membrane is 20x greater than oval window
- Bones of middle ear function as lever
Result is low force, large distance movements of tympanic membrane converted to high force small distance movments to oval window
Impaired function of middle ear?
Conduction Deafness
- Damage to tympanic membrane
- Fluid in middle ear (infection, allergy)
- Otoslerosis (abnormal bone growth in middle ear)
What membrane is distorted to cause bending of auditory hair cell cilia?
Basilar membrane
What structure secretes endolymph
Stria Vascularis
How does the basilar membrane move within the ear?
Perilymph is incompressive, inward movement of oval window causes downward movement of basilar membrane, this pressure is relieve by outward movement of round window
Traveling Wave
Are these uniform?
Traveling Wave - Rapid oscillating deformation of basilar membrane
These are non-uniform due to physical differences along membrane, causing it resonate at different frequencies along its length (optimized)
How are the basilar membrane’s vibrations optimized?
High Frequency - Large deformations near base of cochlea
Medium Frequency - Large deformations near middle of cochlea
Low Frequency - Large deformations near apex of cochlea
What is the nature of the basilar membrane along it’s length?
Base = Narrow and Stiff (high frequency)
Apex = Wife and Floppy (low frequency)
Auditory Hair Cell Function - Membrane Involvement in Sensory Transduction
Explain the Process
Hair cell cilia embedded in basilar membrane contact the tectorial membrane above
The tectorial membrane moves up and down with basilar membrane
The two membranes are on two different pivot points, bending cilia
How is a signal transmitted in hair cell function?
As the membranes move up and down, alternating depolarization and hyperpolarizations
= Increase and decrease in transmitter release
= Increase and decrease in afferent firing
