What do mechanoreceptors do?
Transformation of mechanical stimuli into electrical signal.
What are the two main mechanical receptor-coupled proteins required to generate potential? (Identified via genetic studies in Drosophila and C. Elegans).
- ENaC
- Epithelial sodium channel
- Similar to those responsible for salt-tasting
- TRP
- Transient receptor potential channels
What are statocysts?
- Hollow, fluid-filled cavities
- Contain dense calcium carbonate particles –> statoliths
- Lined with mechanosensory neurons
Describe octopi’s “complex” statocysts.
- Two statocysts
- The cristae detect angilar acceleration
- Macula detects forward acceleration
Where is the “simple ear” in insects?
Sensilla that senses vibration.
What are the three more complicated hearing organs in insects?
- Subgenual organ (legs)
- Johnston’s organ (antenna base)
- Tympanal organ (legs, abdomen, thorax, wing base)
Describe the subgenual organ.
- Eg. cockroaches, honeybees, water striders
- Detects vibrations from ground or water (substrate!)
- Leg vibrations cause subgenual organ to vibrate
- Opens mechanosensitive ion channels
Describe the Johnston’s organ.
- Antenna base
- Eg. moth, fruit fly, mosquitoes
- Detects airboene vibration
- Mechano-sensitive channels are activated
Describe the tympanal organ.
Membrane based “hearing”
Describe the parts involved in vertebrate hearing.
- 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
Describe the mammalian middle ear.
- 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
Describe the mammalian inner ear.
- Coiled cochlea
- Vestibular duct and tympanic duct filled with perilymph
- Cochlear duct filled with endolymph
Explain the importance of tip links.
- 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
Describe signal transduction of the stereocilia of hair cells (hearing).
- 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
Does direction matter in the stimulation of hair cells in the ear?
Yes
- Movement of stereocilia towards kinocilium or longest stereocilia
- depolarization
- Movement away from kinocilium/longest stereocilia
- hyperpolarization
What is the role of tip links?
- Serve as gating mechanism that pulls gates open
- Attached to mechano-gated ion channels via elastic connector proteins that act as springs
Describe the basilar membrane.
- 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
What are the differences between inner and outer hair cells?
- 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
What are the 3 semicircular canals?
- Ampulla
- Utricle
- Saccule
What help utricle and saccules sense linar acceleration?
Otoliths
The utricle detects _______ acceleration and saccules detect _________ acceleration.
Horizontal, vertical
Which of the 3 semicircular canals detect angular momentum?
Ampulla
