Sensory 2 and eyes- Dec. 2nd

Question 1

Photopigments
Rod pigment
Cone pigments

how do they change in light
OPSIN
RETINENE

Answer 1

Photopigments
Rod pigment
- Provide vision only in shades of grey
- Rhodopsin
- Absorbs all/most visible wavelengths
Cone pigments
- Colour Vision
- Red cones. Green cones. Blue cones

Chemical change when activated by light. RHODOPSIN GETS CHANGED
Opsin
* Protein that is integral part of disc membrane
Retinene
* Derivative of vitamin A
* Light-absorbing part of photopigment

Question 2

Resting state – in the Dark
gates, Rods and cones, NT, AP

In Light
photopigment, activate what, gates, membrane, bipolars, ganglions and optic nerve.

Answer 2

Resting-state – in the Dark
- Na+ gates are open
- Rods and cones are depolarized
- Release inhibitory NT. glutamate
- Bipolar cells are inhibited
- No AP’s to ganglions / optic nerve

In Light
- Light breaks down photopigment
- Activates transducin / ↓ cGMP
- Closes Na+ gates
- Hyperpolarizes membrane
- Decreases inhibition of bipolars
* Bipolars excited
* GRADED POTENTIAL’s to ganglions
* ACTION POTENTIAL’s to Optic nerve

Question 3

Colour Blindness

Protanopia
Deuteranopia
Tritanopia

Protanomaly
Deuteranomaly
Tritanomaly

Answer 3

***Poor or lack of function in one or more colour cones
Protanopia
* Lack or red cones
Deuteranopia
* Lack of green cones
Tritanopia
* Lack of blue cones

Protanomaly
* Poor red funcion
Deuteranomaly
* Poor green function
Tritanomaly
* Poor blue function

Question 4

Dark Adaptation
photopigment, threshold, sensitive, Rods, Vitamins? examples

Light Adaptation
photopigment, sensitive. Example

Answer 4

Dark Adaptation
- Go from light to dark
- Re-form more photopigment
- Changes threshold
- Eyes become more sensitive
- More rods used
- Vitamin A needed for regeneration
***Eg. Entering movie theatre

Light Adaptation
- When you go from dark to bright light
- Sudden break-down of photo-pigment
- Bleaching
- Eyes become less sensitive with less photopigment
***Eg. Walking outside after a movie

Question 5

Rods vs Cones
what to what wiring
light needs
receptor field
acuity

Answer 5

Rods
- 100:1 wiring (rods to bipolar)
- Low light is needed to stimulate 1 bipolar
- Larger receptor field
- Poor acuity
Cones
- 1:1 wiring
- Need a lot of light for AP
- Small receptor field
- High acuity