4 - Grover - Auditory and Vestibular Function

Question 1

Specialized Membranes in ciliated hair cells?

Describe each

Answer 1

Apical - Sensory transduction zone, one kinocilium, several stereocilia

Basolateral - resting potential, synaptic transmission zone (CN VIII afferents)

Question 2

Explain sensory transduction in Hair Cells

Explain depolarization, hyperpolarization, and no change

Answer 2

Graded receptor potential by bending cilia

Directionally sensitive:

Toward Kinocilium - depolarization (excite)

Away Kinocilium - hyperpolarization (inhibit)

Perpendicular Kinocilium - No Change

Question 3

Describe the physical process of sensory transduction in hair cells

Answer 3

Bending of cilia pulls open mechanically gates ion channels, located in stereocilia

Stereocilium are mechanically linked

Question 4

Ion Channels in Hair Cells

Answer 4

Cation Channels

K+/Ca2+ permeable

Bending toward opens, bending away closes

Question 5

Describe the Fluid Surrounding Hair Cells and its importance in Sensory Transduction

What is the driving force?

Answer 5

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

Question 6

Consequences of driving force of cations in hair cell membranes?

Answer 6

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

Question 7

Transmitter Release in Hair Cells?

Answer 7

Influx of K+ opens Voltage Gates Calcium Channels

Calcium influx triggers glutamate release via vessicles

NO Action Potentials in hair cells

Question 8

Rates of Transmitter Release in Hair Cells?

Answer 8

Hair cells release glutamate at rest

Bending toward kinocilium increases rate

Bending away kinocilium decreases rate

Question 9

Locations for Vestibular Hair Cells (organs)

Locations for Auditory Hair Cells (organs)

Answer 9

• Otolith Organs (utricle, saccule): Respond to LINEAR ACCELERATION
• Semicircular Canals (ampullae): Respond to ANGULAR ACCELERATION

- - -

Organ of Corti: Respond to SOUND PRESSURE WAVES

Question 10

Otolith Organs:

Organs?

Layers/Components?

Action?

Answer 10

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)

Question 11

Orientation of hair cells in otolith organs?

How does this change?

Answer 11

Adjacent hair cells have similar organization

Orientation changes gradually across maculae, abruptly at striola

Question 12

Difference in Directional Sensitivity in Otolith Organs

Answer 12

Utricle - Horizontal

Saccule - Sagittal

- - -

Maculae on each side are mirror images–Linear acceleration in any direction depolarizes on side, and hyperpolarizes other side

Question 13

Semicircular Canals:

Ampulla

Crista

Cupula

Fluid type?

Answer 13

Ampula - Swelling

Crista - Sensory epithelium

Cupula - Geleatinous mass hair cells extend into

Canals are filled with endolymph

Question 14

What type of motion to semicircular canals detect?

How does this process occur?

Answer 14

Angular Acceleration

When the body is in motion, endolymph lags begind canal–fluid has intertia

The cupula and cilia embedded in it are bent

Question 15

How are Semicircular canals paired?

Answer 15

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

Question 16

How are paired semicircular canals affected by rotation of head?

Answer 16

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

Question 17

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?

Answer 17

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

Question 18

What is the basic journey of sound in the ear?

Answer 18

Outer ear funnels and amplifies sound wave in air, converted to vibrations, converting sound wave in fluid, which is detected by bending of cilia

Question 19

Outer Ear Functions

Loss of function?

Answer 19

1. Amplification (10 dB)
2. 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

Question 20

Middle Ear Function:

Impedance Matching - How?

Answer 20

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

Question 21

Impaired function of middle ear?

Answer 21

Conduction Deafness

• Damage to tympanic membrane
• Fluid in middle ear (infection, allergy)
• Otoslerosis (abnormal bone growth in middle ear)

Question 22

What membrane is distorted to cause bending of auditory hair cell cilia?

Answer 22

Basilar membrane

Question 23

What structure secretes endolymph

Answer 23

Stria Vascularis

Question 24

How does the basilar membrane move within the ear?

Answer 24

Perilymph is incompressive, inward movement of oval window causes downward movement of basilar membrane, this pressure is relieve by outward movement of round window

Question 25

Traveling Wave

Are these uniform?

Answer 25

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)

Question 26

How are the basilar membrane’s vibrations optimized?

Answer 26

High Frequency - Large deformations near base of cochlea

Medium Frequency - Large deformations near middle of cochlea

Low Frequency - Large deformations near apex of cochlea

Question 27

What is the nature of the basilar membrane along it’s length?

Answer 27

Base = Narrow and Stiff (high frequency)

Apex = Wife and Floppy (low frequency)

Question 28

Auditory Hair Cell Function - Membrane Involvement in Sensory Transduction

Explain the Process

Answer 28

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

Question 29

How is a signal transmitted in hair cell function?

Answer 29

As the membranes move up and down, alternating depolarization and hyperpolarizations

= Increase and decrease in transmitter release

= Increase and decrease in afferent firing