Wednesday April 18, 2014. Sensory systems II – color vision and hearing

1. Wednesday April 18, 2014. Sensory systems II – color vision and hearing 1. No Prelecturequiz 3. Review vertebrate eyes 4. Color vision 5. Evolution of the vertebrate eye 6. Intro to hearing

2. http://www.neitzvision.com/content/genetherapy.html

3. Important Point #1. The wavelengths available for sight are relatively limited. Attenuation = the extent to which light is filtered out as it travels through space. Animals living in water can only use a narrow band of spectrum. The rest gets filtered out as it travels through water. The fact that animals rely on such a very narrow band of electromagnetic spectrum supports the idea that animals evolved in water.

4. Important Point #2. Animals use rods and cones to detect light. Rods and cones contain photopigment. Different cones (and rods) contain different types of photopigments (also called rhodopsins). Rods function in dim light. Cones function in color vision.

6. All animals detect light using photopigment (i.e. rhodopsin) that consists of combining an opsin protein with retinal (vitamin A). The mechanism of initial light detection is highly conserved. When light of the right wavelength strikes the photopigment, the photopigment changes shape. This starts a signal transduction cascade.

7. Vertebrates In vertebrates, in the dark, the rod/cone cells are "on" (i.e. relatively depolarized & releases neurotransmitter) In the dark, rod sends message saying "don't fire" to the bipolar cell. In the light, the rod stops sending this message and the bipolar cell fires (i.e. triggers an action potential).

8. Important Point #3. Cone cells and rod cells point to the back of your eyeball. They don’t face the light. In fact, all vertebrates (including you) see through a layer of nerve cells.

9. Even within vertebrates, visual properties vary widely among species. Let's consider color vision.

10. Relative Probability of Absorption Does the blue absorb light at 450 nm? A. Yes B. No

11. Relative Probability of Absorption Does the blue absorb light at 600nm? A. Yes B. No

12. Humans have 3 different cone cells – a red, a green and blue. Relative Probability of Absorption

13. 3. Animals differ in how many types of cones they have and in the sensitivities of those cones.

14. Bluefin Killifish

15. Lots of major types of “color”. Bluefin killifish have 5 cones!

16. If bluefin killifish have 5 different cone cell types, then how many different types of opsins do they have? A. 3 B. 4 C. 5 D. 6 E. 7

17. Radio Lab: http://www.radiolab.org/story/211178-rip-rainbow/ http://www.nature.com/news/mantis-shrimp-s-super-colour-vision-debunked-1.14578

18. Cosmos - evolution of the eye • http://www.openculture.com/2014/03/neil-degrasse-tyson-tells-fox-viewers-evolution-is-a-scientific-fact-on-cosmos.html

19. Captures and funnels sound to tympanic membrane

20. Townsend's big-eared bat (Corynorhinus townsendii)

21. Amplifies sound and transfers energy the oval window

22. Hearing- Mammals (con’t) • Pathway: • Sound waves in air travel through outer ear until they reach tympanic membrane • Sound waves vibrate membrane, which in turn vibrates 3 bones of middle ear: Malleus Incus Stapes (outin: “MIS”)

23. Hearing- Mammals (con’t) • Pathway: • Stapes transmits sound to the oval window -membrane on the surface of cochlea

24. Detects sound frequency transmits signal to the auditory nerve

25. Hearing- Mammals (con’t) • Pathway: • Stapes transmits sound to the oval window -membrane on the surface of cochlea • Vibration on oval window causes vibration of perilymph (fluid) in the cochlea