Hearing and Vestibular Lecture (Dr. Karius) TEST 2

Question 1

Hearing

Answer 1

The Outer, Middle, and Inner Ear each play an Important role in Hearing
1) OUTER EAR: Funnel the Sound Waves into the Ear

2) MIDDLE EAR: Impedance matching, the sound wave has been moving though AIR, but now we are going to have it move in Liquid/ Water
3) INNER EAR: COCHLEA coverts the Sound Waves to ACTION POTENTIALS

Question 2

Cochlea

Answer 2

1) The SCALA VESTIBULE is the MOST SUPERIOR

** The REISSNER’S MEMBRANE separates the Scala Bestibuli with the Scala Media

2) The SCALA MEDIA is in the MIDDLE

• ** The BASILAR MEMBRANE separates the Scala Media and the Scala Tympani
• It is important with SOUND!!!

3) The Most INFERIOR Compartment is the SCALA TYMPANI

Question 3

Hearing, circulation between the Scala Vestibule and Scala Tympani

Answer 3

*** The SCALA VESTIBULE and the SCALA TYMPANI are continuous, Fluid- filled compartments. The Fluid inside is PERILYMPH!!!!

Helicotrema

Question 4

Perilymph

Answer 4

• Contents are similar to ECF

- Contains HIGH Na+ and LOW K+

Question 5

Hearing with the Basiar and Reissner’s Membranes

Answer 5

• The BASILAR and REISSNER’S MEMBRANE create a Chamber (The Scala Media) that is ISOLATED from Perilymph
• ENDOLYMPH (Fluid inside the Scala Media) is HIGH in K+ and LOW in Na+

**The Composition of the Endolymph will have a SIGNIFICANT EFFECT on the TRANSDUCTION of SOUND WAVES int ACTION POTENTIALS

Question 6

Compare and Contrast Perilymph and Endolymph

Answer 6

1) PERILYMPH
- Found in the Scala Vestibule and Scala Tympani
- Most similar to ECF/ CSF
- HIGH in Na+ and LOW in K+

2) ENDOLYMPH
- Found in the Scala Media
- Most similar to INTRACELLULAR FLUID
- HIGH in K+ and LOW in Na+

***If something disrupts the Endolymph and Perilymph distributions, then HEARING will be profoundly IMPACTED!!!

Question 7

External Ear

Answer 7

• Crucial for “FUNNELING” the Sound Waves into the EAR
• Head motions are Crucial to helping this happen, we will turn TOWARDS the NOISE to Improve the ability of the EAR to COLLECT the SOUND WAVES

Question 8

Middle Ear

Answer 8

• The MIDDLE EAR transmits the Sound Waves from the AIR Environment of the Middle Ear to the AQUEOUS Environment of the COCHLEA
• The OSSICLES Transmit and AMPLIFY the COCHLEA!!!!

Question 9

Inner Ear

Answer 9

• In the Inner Ear, the IMPACT of the STAPES on the Oval Window causes the BASILAR MEMBRANE to Virabte at the SAME FREQUENCY of the Sound (Down with Impact, Up with Release)

1) COMPRESSION of STAPES on OVAL WINDOW:
- Stapes moving IN Causes a DOWNWARD Motion of the BASILAR MEMBRANE

2) RAREFACTION of the STAPES on the OVAL WINDOW:
- Stapes Moving OUT causes an UPWARD Motion of the BASILAR MEMBRANE

Question 10

High Frequency and Low Frequency Waves

Answer 10

1) HIGH FREQUENCY Sound (Short Wavelengths) :
- Cause the MAXIMUM VIBRATION of the Basilar Membrane CLOSEST to the OVAL WINDOW

2) LOW FREQUENCY Sound (Long Wavelengths):
- Sounds cause the MAXIMUM Vibration of the Basilar Membrane FARTHEST AWAY from the OVAL WINDOW (Towards the HELICOTREMA)

Question 11

Organ of Corti

Answer 11

• Has a TECTORIAL MEMBRANE that DOESNT Connet all the way across and DOESNT MOVE when he Basilar Membrane moves
• There are Inner and Outer HAIR CELLS embedded into the TECTORIAL MEMBRANE

***The OUTER HAIR CELLS are the ones important for HEARING!!!!!!!!

Question 12

Hair Cells

Answer 12

• Each Hair Cell is composed of a distinct arrangement of Shorter STEREOCILIA that INCREASE in Length. The Stereocilia are NOT true Cilia
• Each Stereocilia is connected to other at the top by an Extracellular Filamentous Protein. This protein filament is known as the TIP LINK
• During development, there is a SINGLE TRUE Cilium, the KINOCILIUM!!!!!!
• The KINOCELIUM is the TALLEST of the “Hairs” on the Hair Cell. In Mammals, it degenerates beginning around the time of Birth

Question 13

Movement of the Basilar Membrane and result on Tectorial Membrane

Answer 13

**When sound causes the Basilar Membrane to VIRBATE, the Connections between the Basilar Membrane and the Tectorial Membrane cause the TECTORIAL MEMBRANE to move as well. THIS MOTION BENDS THE HAIR CELLS!!!!!!

• During TRANSDUCTION, if the STEREOCILI are Bent TOWARDS the KINOCILIUM, the Hair Cell DEPOLARIZES!!!!!!

**Bending the Hair Cells TOWARDS the Kinocilium OPENS POTASSIUM CHANNELS that DEPOLARIZE the Cell. Due to the Composition of the Endolymph, POTASSIUM ENTERS the Hair Cells and causes it to DEPOLARIZE Calcium is also Involved!! **

• If the STEREOCILIA move AWAY from the KINOCILIUM, the Hair Cell HYPERPOLARIZES!!!!!!

Question 14

Summary of Depolarization of the Hair Cells

Answer 14

1) Sound Waves are funneled into the Ear by the EXTERNAL EAR
2) The Middle Ear OSSICLES are required to generate enough Force to cause the Water-filled COCHLEA to Vibrate at the Frequency of the Sound (IMPEDANCE MATCHING)

3) In the Cochlea:
a) Vibration of the Basilar Membrane is determined by the Frequency of the Sound
- HIGH Frequency Sounds are near the BASE of the Basilar Membrane

• LOW Frequency Sounds are Near the BASE of the Basilar Membrane
  b) The Vibration causes BENDING of the Hair Cells
  c) DEPOLARIZATION of the Hair Cells is produced by INFLUX of K+ and probably Ca2+

Question 15

Pathways in the Cochlea

Answer 15

1) VENTRAL Pathway:
- Starts processing of TEMPORAL and SPECTRAL features of the Sound (Tells about the Sound)

2) DORSAL Pathway:
- Integrates the ACOUSTIC Information with SOMATOSENSORY Information for LOCALIZING SOUND (Where the Sound Started)

3) The MEDIAL SUPERIOR OLIVE generates a MAP of the INTRA-AURAL TIME DIFFERENCES (How the sound arrived at the two Ears differently)
- Sound will reach one ear milliseconds before it reaches the other ear

4) The LATERAL SUPERIOR OLIVE generates a Map of the INTRA-AURAL INTENSITY DIFFERENCES (How the Sound arrived at the Two Ears differently)
- If the Left Ear is farther away from the source of the sound, the Intensity (Amplitude) of the Sound is SLIGHTLY REDUCED compared to what the Right Ear detected!!!!

TIME and INTENSITY differences are CRUCIAL INFORMATION in Determining where a SOUND Originated from!!!!*

5) INFERIOR COLLICULUS:
- SUPPRESSES Information relates to Echoes (They Interfere with Location) and arrives at a FINAL Estimation of the SOUND LOCATION on the Horizon (Horizontal Plane)

6) SUPERIOR COLLICULUS:
- Takes the Location Data from the Inferior Colliculus and ADDS the THIRD DIMENSION to it (VERTICAL HEIGHT) to create the Spatial Map of the Sound’s LOCATION (ADDS DEPTH)

Question 16

Primary Auditory Cortex and Auditory Association Cortex

Answer 16

1) The PRIMARY AUDITORY CORTEX (A1) has a TONOTOPIC (Orientated by Tone) representation of the Sounds, More ROSTRAL area are ACTIVATED by LOW FREQUENCY Sounds, while CAUDAL area receive Information about HIGH FREQUENCY Sounds
- There are several other Characteristics of the Sound that Map to areas of A1, including Loudness and Modulations in Volume, Rate of Frequency Modulation

2) AUDITORY ASSOCIATION CORTEX:
- Is composed of Several Different Types of areas (BROCA’S, WERNICKE’S, etc). A1 has a lot of Neurons that detect PURE TONES while the ASSOCIATION Cortex, in Contract, has more Neurons that are activated by COMPLEX SOUNDS

Question 17

Summary of Cochlea and Cortexes

Answer 17

1) COCHLEAR NUCLEI:
• VENTRAL: the Nature of the sound (high,low)
• DORSAL: the Location of the sound

2) SUPERIOR OLIVE:
• Medial: differences in time of arrival to the ears
• Lateral: differences in intensity

3) INFERIOR COLLICULUS: Spatial map of sound (where is it coming from)
4) PRIMARY AUDITORY CORTEX (A1) – tonotopic map, beginning to know WHAT the Sound is.

5) ASSOCIATED AUDITORY CORTICAL AREAS:
• PROCESSING of complex sounds (e.g.music)
• IDENTIFICATION of sound (naming)
• SPEECH

Question 18

Vestibular

Answer 18

• The Inner ear also contains the SENSORY Receptors that will tell us about ACCELERATION. Linear Acceleration is a MOTION that occurs in Either the Horizontal or Vertical Plane
• ANGULAR ACCELERATION requires Rotation around One ro More Planes

Question 19

Vestibular Summary

Answer 19

1) LINEAR ACCELERATION:
- MOVING along a LINE (Particularly the Head)
- HORIZONTALLY (Walking is a Good Example of a Linear Acceleration)
- VERTICALLY (Jumping Up or Down is a Good Example)

2) ANGULAR (Rotational) Acceleration:
- The motion includes Rotation (Spinning or Turning)
- Can:
a) Spin around a VERTICAL AXIS
b) Fall FORWARD
c) Fall BACKWARD
d) Each of these will have different effects.

3) IN Real Life Most of our MOTIONS are COMBINATIONS of SEVERAL of these!!!

Question 20

Vestibular Parts

Answer 20

• Acceleration in these Different Planes is DETECTED by the SEMICIRCULAR CANALS, the UTRICLE (Swelling where all three Canals Connect), and the SACCULE (Below the Utricle). Each is ORIENTED to be BEST at Detecting Acceleration in ONE of the Planes
• Just like in the Cochlea, we have ENDOLYMPH (High K+) INSIDE each of these Five Regions. PERILYMPH (High Na+) si=urrounds the Vestibular Apparatus (between the Membranes you see here and the Bone, which you dont see)

Question 21

Utricle

Answer 21

• The UTRICLE is best situated to Detect LINEAR MOTION occurring on the HORIZONTAL PLANE

Question 22

Saccule

Answer 22

• The SACCULE is best positioned for VERTICAL (UP and DOWN) Acceleration

Question 23

Semicircular Canals

Answer 23

1) HORIZONTAL SEMICIRCULAR CANALS:
- A TURNING Motion is BEST Detected by the Horizontal (Lateral) Canals

2) POSTERIOR SEMICIRCULAR CANAL:
- Falling (or being thrown BACKWARDS) MAXIMALLY Activates the Posterior Semicircular Canal

3) ANTERIOR SEMICIRCULAR CANAL:
- While Falling FORWARDS Maximally activates the Anterior Semicircular Canal

Question 24

Vestibular Organs

Answer 24

• The process of ACTIVATING the difference Vestibular Organs is SIMILAR to that we saw in the Cochlea, Movement of HAIR CELLS in ONE Direction is EXCITATORY, and Movement in the OPPOSITE Direction INHIBITS.
• In the Semicircular Canals, the AMPULLA is Specialized for this PROCESS!!!!!!
• Movement stimulates Hair Cells, which send a Signal through the SENSORY NERVE***
• In the Utricle and Saccule (The Otolith Organs), the MACULA is Specialized for this Process!!!

Question 25

Vestibular Motion

Answer 25

• Motion of the BODY (Particularly the Head) will produce Motion of the ENDOLYMPH in the appropriate Vestibular Organ, bending the Hair Cells the AMPULLAE or MACULA (Depending on the Type of Motion) and activating the Nerves

Question 26

Summary of Forces that activate the Vestibular Components

Answer 26

1) ANTIEOR Semicircular Canal: Falling FORWARD
2) HORIZONTAL Semicircular Canal: SPINNING
3) POSTERIOR Semicircular Canal: Falling BACKWARD
4) UTRICLE: WALKING Forward
5) SACCULE: Jumping UP or DOWN

In All Cases:

• The Motion starts ENDOLYMPH MOVIGN
• Causing Beinding of the Hair Cells
• Initiation of Action Potentials

Question 27

Vestibule- Optic Reflexes

Answer 27

• Regardless of which war we are falling/ Moving, the Reflexes are designed to keep our FOCUS on the Horizon (a Spot directly in Front of us)
• As I spin to execute my Kick, my eyes Rotate HORIZONTALLY (Side to Side) until I can no Longer Physically Focus on that Spot, at which time they Jump to pick a New Spot
• If I fall FORWARD: My Eyes Move UP!!!
• If i Fall BACKWARDS: My Eyes Move DOWN!!!!!

Question 28

Muscles activated while Moving

Answer 28

1) If the ANTERIOR Semicircular Canal is ACTIVE, the SUPERIOR RECTUS MUSCLE is ACTIVATED while the INFERIOR RECTUS is INHIBITED. My Eyes move UP to Continue to Focus as I Fall Forward

2) If the POSTERIOR Semicircular Canal is ACTIVE, the SUPERIOR OBLIQUE MUSCLE is ACTIVATED while the INFERIOR OBLIQUE is INHIBITED.
- My eyes move DOWN to Continue to Focus on a Point as I Fall Backward

3) If the HORIZONTAL (Lateral) Semicircular Canal is ACTIVE

Question 29

Summary of Vestibule- Optic Reflexes

Answer 29

GOAL: Maintain Focus on a Point on Horizon in Front of US until Impossible to do so

1) If Im falling FORWARD, my Eyes go UP (SUPERIOR RECTUS)
2) If Im falling BACKWARD, Eyes of DOWN (SUPERIOR OBLIQUE)
3) If Im Spinning, it depends on the Direction of my TURN, but MEDIAL and LATERAL RECTUS MUSCLES are Invovled

Question 30

Cerebral Cortex and Cerebellum in Integration of Vestibular Information and Control of Gaze

Answer 30

• The Vast Majority of the CORTICAL and CEREBRAL Involvement in the VESTIBULOOPTIC Reflexes is to SUPPRESS THE REFLEC TO ALLOW FOR VOLUNTARY MOTION!!!!!!!!!!