Transcript The process by which the sensitivity to a certain sensory __________.

The process by which the sensitivity to a certain
stimulus is modified by previous exposure is called
sensory __________.
A) transduction
B) adaptation
C) modulation
D) amplification
E) range fractionation
Each taste bud is composed of taste cells,
supporting cells, and basal cells.
A) True
B) False
T F In order for taste and/or olfaction to occur, the
chemical being sensed must be first be in
solution.
Outline
I. How do our eyes sense light
II. How our eyes adapt to the light & dark
Back
of Eye
Front
of Eye
Choroid
Rods &
Cones
Bipolar Ganglion
Cells
Cells
Back
of Eye
Front
of Eye
Visual Pathway of the Retina
• Rods & Cones
–
–
–
–
Photoreceptors of eye
some convergence occurs
100 million rods/eye
3 million cones/eye
Visual Pathway of the Retina
• Rods & Cones
–
–
–
–
Photoreceptors of the eye
some convergence occurs
100 million rods in each eye
3 million cones in each eye
• Bipolar cells
– synapse with ganglion cells
– large amount of convergence
Visual Pathway of the Retina
• Rods & Cones
–
–
–
–
Photoreceptors of the eye
some convergence
100 million rods in each eye
3 million cones in each eye
• Bipolar cells
– synapse with ganglion cells
– lots of convergence
• Ganglion cells
– axons of these form optic nerve
– more convergence
Rods:
• High sensitivity
• Low acuity
• Allow “night vision”
• Outside fovea
Rod
Rods:
• High sensitivity
• Low acuity
• Allow “night vision”
• Outside fovea
Cones:
• Low sensitivity
• High acuity
• Allow color vision
• Mainly in fovea
Rod
Cone
Rod and Cone Distribution in Eyes
Structure of a Rod
Outer
Segment
(contains
photopigment)
Inner
Segment
Photopigments: Light-sensitive Proteins
• Photopigment of rods is ____________
Photopigments: Light-sensitive Proteins
•
Photopigment of rods is ____________
•
Photopigments have two parts:
1) protein called opsin
2) derivative of vitamin A called retinal
Photopigments: Light-sensitive Proteins
•
Photopigment of rods is ____________
•
Photopigments have two parts:
1) protein called opsin
2) derivative of vitamin A called retinal
•
Cones contain photopsin
–
–
Opsins have different amino acids that determine
which wavelengths are absorbed
Red, green, and blue cones absorb red, green, and
blue light, respectively
Selectivity of Rods & Cones
Rods are generalists
Cones are specialists
- Blue cones
- Green cones
- Red cones
Cone Absence leads to Colorblindness
Red-Green Colorblindness:
results from absence of red
or green cones in retina
Transduction in Rods and Cones
• In complete darkness, rods and cones are
___________ by influx of Na+
Transduction in Rods and Cones
• In complete darkness, rods and cones are
___________ by influx of Na+
• Send IPSP’s to bipolar neuron
Transduction in Rods and Cones
• In complete darkness, rods and cones are
___________ by influx of Na+
• Send IPSP’s to bipolar neuron
• Light stimulates breakdown of photopigments
Transduction in Rods and Cones
• Photopigment breakdown results in the closing
of Na+ channels
Transduction in Rods and Cones
• Photopigment breakdown results in the closing
of Na+ channels
• IPSP’s stop
Total Dark
Na+ Influx
(depolarization)
IPSP’s to
Bipolar Neuron
No AP to
Ganglion Cell
No AP to
Visual Cortex
Total Dark
Light
Na+ Influx
(depolarization)
Photopigment
Breakdown
IPSP’s to
Bipolar Neuron
Na+ channels
Close
No AP to
Ganglion Cell
Stop IPSP’s
to BPN
No AP to
Visual Cortex
AP sent to
Ganglion Cell
AP sent to
Visual Cortex
Outline
I. How do our eyes sense light
II. How our eyes adapt to the light & dark
Light/Dark Adaptation of Eyes
Dark Adaptation of Eyes
• Visual sensitivity depends on concentration of
photopigments
Dark Adaptation of Eyes
• Visual sensitivity depends on concentration of
photopigments
When first entering the dark theatre, you see:
Dark Adaptation of Eyes
• Photopigments broken down by light
Dark Adaptation of Eyes
• Photopigments broken down by light
• Photopigments regenerated in the dark
(created faster than broken down)
Dark Adaptation of Eyes
• Photopigments broken down by light
• Photopigments regenerated in the dark
(created faster than broken down)
• Highly-sensitive rods “turned on”
Light Adaptation of Eyes
When leaving the theater ….
• Eyes highly sensitive to bright light
Light Adaptation of Eyes
• Photopigments break down
Light Adaptation of Eyes
• Photopigments break down
• Light sensitivity decreases
Light Adaptation of Eyes
• Photopigments break down
• Light sensitivity decreases
• Rods “burned out” as rhodopsin is
broken down
Light Adaptation of Eyes
• Photopigments break down
• Light sensitivity decreases
• Rods “burned out” as rhodopsin is
broken down
• Brain switches vision from _____ to _____
Changes in Pupil Size
• Circular and Radial Muscles
• Pupil size controlled by sympathetic and
parasympathetic nervous stimulation
Dude, What Just Happened?
Summary
• Rods allow high sensitivity/low acuity night
vision; Cones allow low sensitivity/high acuity
daylight vision
• Vision is somewhat counterintuitive
• Photopigment breakdown and regeneration,
change in pupil diameter, and switching of
photoreceptor type allows for light/dark
adaptation of the eyes