Hearing

Question 1

What do mechanoreceptors do?

Answer 1

Transformation of mechanical stimuli into electrical signal.

Question 2

What are the two main mechanical receptor-coupled proteins required to generate potential? (Identified via genetic studies in Drosophila and C. Elegans).

Answer 2

• ENaC
  
  • Epithelial sodium channel
  • Similar to those responsible for salt-tasting
• TRP
  
  • Transient receptor potential channels

Question 3

What are statocysts?

Answer 3

• Hollow, fluid-filled cavities
• Contain dense calcium carbonate particles –> statoliths
• Lined with mechanosensory neurons

Question 4

Describe octopi’s “complex” statocysts.

Answer 4

• Two statocysts
• The cristae detect angilar acceleration
• Macula detects forward acceleration

Question 5

Where is the “simple ear” in insects?

Answer 5

Sensilla that senses vibration.

Question 6

What are the three more complicated hearing organs in insects?

Answer 6

• Subgenual organ (legs)
• Johnston’s organ (antenna base)
• Tympanal organ (legs, abdomen, thorax, wing base)

Question 7

​Describe the subgenual organ.

Answer 7

• Eg. cockroaches, honeybees, water striders
• Detects vibrations from ground or water (substrate!)
• Leg vibrations cause subgenual organ to vibrate
• Opens mechanosensitive ion channels

Question 8

Describe the Johnston’s organ.

Answer 8

• Antenna base
• Eg. moth, fruit fly, mosquitoes
• Detects airboene vibration
• Mechano-sensitive channels are activated

Question 9

Describe the tympanal organ.

Answer 9

Membrane based “hearing”

Question 10

Describe the parts involved in vertebrate hearing.

Answer 10

• Multiple mechanosensory cells
• Mechanoreceptor cells - modified **epithelial cells **that synapse with a sensory neuron
• Hair cells
  
  • Kinocilium (not present in adult mammals)
  • Stereocilia
    
    • Connected via tip links

Question 11

Describe the mammalian middle ear.

Answer 11

• Improves detection of sounds in air
• Air-filled space
  
  • Separated from outer ear by tympanic membrane
  • Separtated from inner ear by oval window
• Sound waves –> middle ear
  
  • Tympanic membrane vibrates
  • Vibration transferred from malleus to incus to stapes to oval window

Question 12

Describe the mammalian inner ear.

Answer 12

• Coiled cochlea
• Vestibular duct and tympanic duct filled with perilymph
• Cochlear duct filled with endolymph

Question 14

Explain the importance of tip links.

Answer 14

• Stereocilia connected to each other via tip links
• Critical for mechanosensitivy
  
  • Removal of tip links results in loss of voltage response
• Protein recently identified as protocadherin 15

Question 15

Describe signal transduction of the stereocilia of hair cells (hearing).

Answer 15

• Mechanosensitivy ions channels near tips of stereocilia
• Channels are constitutively open
  
  • at rest ~ 15% channels open - giving a resting membrane potential of -60 mV
  • small # Ca²⁺ channels open
  • some NT release
  • modest APs in afferent neuron

Question 16

Does direction matter in the stimulation of hair cells in the ear?

Answer 16

Yes

• Movement of stereocilia towards kinocilium or longest stereocilia
  
  • depolarization
• Movement away from kinocilium/longest stereocilia
  
  • hyperpolarization

Question 17

What is the role of tip links?

Answer 17

• Serve as gating mechanism that pulls gates open
• Attached to mechano-gated ion channels via elastic connector proteins that act as springs

Question 18

Describe the basilar membrane.

Answer 18

• Stiff and narrow at attachments near round and oval windows
  
  • Vibrates for high frequency sound
• Wider and more flexible at distal end
  
  • Vibrates for low frequency sound

Question 19

What are the differences between inner and outer hair cells?

Answer 19

• Inner
  
  • loud signal
  • increased depolarization of hair cells
  • increased frequency of APs
• Outer
  
  • amplify sound; a noise causes depolarization, voltage-sens protein contracts causing the basilar membrane to become more responsive to sound
  • change shape in response to sound waves rather than release NT
  • tempers the amount of the basilar membrane moves in response to a sound
  • form synapses with effernt neurons
    
    • ACh released in response to loud noises

Question 20

What are the 3 semicircular canals?

Answer 20

• Ampulla
• Utricle
• Saccule

Question 21

What help utricle and saccules sense linar acceleration?

Answer 21

Otoliths

Question 22

The utricle detects _______ acceleration and saccules detect _________ acceleration.

Answer 22

Horizontal, vertical

Question 23

Which of the 3 semicircular canals detect angular momentum?

Answer 23

Ampulla