1. Lecture 16 : Hearing
Fain ch 6
10/28/09

2. Midterm project Dr. Payne is in search of - # trp channels in inverts
Is there conservation of pore - Ca+2 selectivity
Evolutionary constraint across inverts
All inverts have the same Ca+2 selectivity
All have D621
There is more than one type of invert Trp
Might differ in pore region, D621

3. Align w/ Drosophila Trp

4. Tree
TrpN
TrpV
TrpM
TrpC
TrpA

5. Trp M D
Trp C

6. How should we name sequences for big tree?
Dme = First letter of Genus , 1st two of species
Add last four or five numbers of gene #
Gi| |

7. What do you want for an outgroup?
Possibilities:
Make fasta file with all of your sequences + Dr Paynes limulus + outgroup + Drosophila trp + trpl + trpgamma + Human trpC1 and 3

8. What data should each of you give him?
Table of genes - acc# - Trp box1 seq - pore site (5 AA) - site 621
Notes - ex. Missing pore region - ignored
Tree w/ TrpM, N, V , A

9. How should we present data to Dr. Payne next week?
Tree -
For TrpCs label pore site and Trp box1

10. To do list Today - Fasta file with renamed seqs
Next week - one ppt slide with tree (TrpCs labeled with pore)
Stuff ed to Dr Payne
Wait till after class on Wed

11. Monday I will be visiting Duke to give a seminar
Dr. Chris Hofmann will give a lecture on vertebrate vision and my favorite cichlid fish
He can answer questions on phylogenetics

12. Questions What is the structure of the ear?
Why are hair cells important?
How do hair cells transmit signals?
What molecules are important?

13. Hearing is a key sense
Detect sound
Intensity
Frequency
Direction

14. Ear

15. Vestibular organs Semicircular canals Otolith organs Anterior
Posterior
Lateral
Otolith organs
Utriculus
Sacculus
Lagena (sometimes)
Anterior
Posterior
Lateral
Hair cells in ampullae

16. Hair cells in ampulae All hair cells point same way in a given canal
Detect fluid or otolith motion
Fig 6.15

17. Vestibular
Endolymph
High in Ca+2 K+
Depolarize when K+ enters through hair cell channels

18. Sensing head motion
Fig 6.16

19. Hair cells in semicircular canals
Detect position and movement of head
Hair cells detect motion in different directions
Fig 6.1

20. Neuromast with cupula Cupula - gelatinous covering
Cupula - gelatinous covering

21. Ear

22. Middle ear

23. Inner ear Semicircular canals Cochlea

24. Cochlea has hair cells supported by basilar membrane
Basilar membrane responds to high, med and low freq as move down the cochlea

25. Organ of Corti
15,000 hair cells in mammals
Fig 6.18

26. Hair cells in cochlea Inner hair cells
Organ of Corti on basilar membrane
Outer hair cells
Cochlear hair cells have lost kinocilium

27. Organ of Corti Stereocilia bathed by endolymph: K+ rich
Tectorial membrane
Stereocilia bathed by endolymph: K+ rich
Rest of cochlea bathed in perilymph Na+ rich
Fig 6.18

28. Frequency response Frequency response differs down membrane
Frequency response differs down membrane
Actual freq response is narrower than expect

29. Cochlear amplifier Inner hair cells make 90-95% of neural connections
Outer hair cells
Tune frequency response
Change shape in response to sound
Depolarize - shorten
Hyperpolarize - lengthen
Motion conferred by protein called prestin
Moves Organ of Corti up and accentuates basilar membrane motion

30. Hair cells

31. Electrical resonance
Cells have frequencies at which respond maximally to oscillating potential
Response to sounds at resonant frequency will be amplified
Cells differ in electrical response down cochlea
Difference in Ca+2 gated K+ channels

32. Cell response Mechanosensation - depolarize
Opens voltage gated Ca+2 channels - depolarize and let in Ca+2
Ca+2 triggers Ca+2 gated K+ channels - hyperpolarize
Density of channels and properties of Kca channels will “tune” resonant frequency
Depolarization changes membrane potential. This potential change opens the voltage gated Ca channels. These depolarize and let calcium in. Calcium gates the calcium gated potassium channels which hyperpolarize - let K out.

33. Electrical resonance
Cells have frequencies at which respond maximally to oscillating potential
Response to sounds at resonant frequency will be amplified
Cells differ in electrical response down cochlea
Difference in Ca+2 gated K+ channels