Wednesday April 18, 2014.

Sensory systems II – color vision and hearing

1. No Prelecture quiz3. Review vertebrate eyes4. Color vision5. Evolution of the vertebrate eye6. Intro to hearing

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

Important Point #1. The wavelengths available for sight are relatively limited.

The fact that animals rely onsuch a very narrow band of electromagnetic spectrumsupports the idea that animalsevolved in water.

Animals living in water canonly use a narrow bandof spectrum. The rest getsfiltered out as it travelsthrough water.

Attenuation = the extent towhich light is filtered out asit travels through space.

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.

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.

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).

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.

Even within vertebrates, visual properties vary widely among species.

Let's consider color vision.

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Does the blue absorb light at 450 nm?

A. YesB. No

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Does the blue absorb light at 600nm?

A. YesB. No

Humans have 3 different cone cells – a red, a green and blue. R

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

Bluefin Killifish

0

0.2

0.4

0.6

0.8

1

350 400 450 500 550 600 650 700 750

wavelength

absorbance

Bluefin killifish have 5 cones!

Lots of major types of “color”.

If bluefin killifish have 5 different cone cell types, then how many different types of opsins do they have?

A. 3B. 4C. 5D. 6E. 7

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

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

Captures and funnels sound to tympanic membrane

Townsend's big-eared bat (Corynorhinus townsendii)

Amplifies sound and transfers energy the oval window

• Pathway:1. Sound waves in air

travel through outer ear until they reach tympanic membrane

2. Sound waves vibrate membrane, which in turn vibrates 3 bones of middle ear:

MalleusIncusStapes(outin: “MIS”)

Hearing- Mammals (con’t)

• Pathway:

3. Stapes transmits sound to the oval window

-membrane on the surface of cochlea

Hearing- Mammals (con’t)

Detects sound frequency transmits signal to the auditory nerve

• Pathway:

3. Stapes transmits sound to the oval window

-membrane on the surface of cochlea

4. Vibration on oval window causes vibration of perilymph (fluid) in the cochlea

Hearing- Mammals (con’t)