The process by which the sensitivity to a certain stimulus is modified by previous exposure is called sensory __________.

A) transductionB) adaptationC) modulationD) amplificationE) range fractionation

Each taste bud is composed of taste cells, supporting cells, and basal cells.

A) TrueB) 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

Backof Eye

Frontof Eye

BipolarCells

Rods &Cones

GanglionCells

Choroid

Frontof Eye

Backof 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

Rod

Rods:• High sensitivity• Low acuity• Allow “night vision”• Outside fovea

Rod Cone

Rods:• High sensitivity• Low acuity• Allow “night vision”• Outside fovea

Cones:• Low sensitivity• High acuity• Allow color vision• Mainly in fovea

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 opsin2) derivative of vitamin A called retinal

Photopigments: Light-sensitive Proteins• Photopigment of rods is ____________

• Photopigments have two parts:1) protein called opsin2) 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)

No AP to Ganglion Cell

IPSP’s to Bipolar Neuron

No AP to Visual Cortex

Total Dark

Na+ Influx(depolarization)

No AP to Ganglion Cell

IPSP’s to Bipolar Neuron

No AP to Visual Cortex

Light

PhotopigmentBreakdown

Na+ channelsClose

Stop IPSP’s to BPN

AP sent to Ganglion Cell

AP sent toVisual Cortex

Outline

I. How do our eyes sense light

II. How our eyes adapt to the light & dark

Light/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”

Dark Adaptation of Eyes

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