Transcript Lecture_33x - life.illinois.edu.

Wednesday April 18, 2014.
Sensory systems II – color vision and hearing
1. No Prelecture quiz
3. Review vertebrate eyes
4. Color vision
5. Evolution of the vertebrate eye
6. Intro to hearing
http://www.neitzvision.com/content/genetherapy.html
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.
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.
Relative Probability of Absorption
Does the blue absorb light at 450 nm?
A. Yes
B. No
Relative Probability of Absorption
Does the blue absorb light at 600nm?
A. Yes
B. No
Relative Probability of Absorption
Humans have 3 different cone cells – a red, a green and blue.
3. Animals differ in how many types of cones they have and in the sensitivities of those
cones.
Bluefin Killifish
Lots of major types of “color”.
Bluefin killifish have 5 cones!
1
absorbance
0.8
0.6
0.4
0.2
0
350
400
450
500
550
wavelength
600
650
700
750
If bluefin killifish have 5 different cone cell types,
then how many different types of opsins do they
have?
A.
B.
C.
D.
E.
3
4
5
6
7
Radio Lab: http://www.radiolab.org/story/211178-rip-rainbow/
http://www.nature.com/news/mantis-shrimp-s-super-colour-vision-debunked-1.14578
Cosmos - evolution of the eye
• http://www.openculture.com/2014/03/neildegrasse-tyson-tells-fox-viewers-evolution-isa-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
Hearing- Mammals (con’t)
• 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:
Malleus
Incus
Stapes
(outin: “MIS”)
Hearing- Mammals (con’t)
• Pathway:
3. Stapes transmits sound to
the oval window
-membrane on the
surface of cochlea
Detects sound frequency
transmits signal to the auditory
nerve
Hearing- Mammals (con’t)
• 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