Sensory 2 and eyes- Dec. 2nd

Question 1

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

on the table:
number of?
vision in what colour?
sensitivity?
acuity?
night or day?
convergence?
concentrated where?

Answer 1

Rods
- 100:1 wiring ( 100 rods to 1 bipolar)
- somewhere within those hundred rods something got hit
- Low light is needed to stimulate 1 bipolar. night time
**Larger receptor field
- Poor acuity. can’t localize

Cones
- 1:1 wiring
- NEED a lot of light for AP. daytime
***Small receptor field. Can localize and know exactly where it is
- High acuity

Question 2

Photopigments

Rod pigment
rhodopsin?

Cone pigments
cones?

Answer 2

Photopigments. Light breaks down photopigment. triggers a chemical change. triggers a response to become Graded potential

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

Question 3

Photopigments
how do they change in light?
rhodopsin becomes?

Answer 3

Chemical change when activated by light.

RHODOPSIN GETS CHANGED into opsin and retinene

Opsin
* Protein that is integral part of disc membrane

Retinene
* Derivative of vitamin A
* Light-absorbing part of photopigment
if vitamin a deficiency, can see particularly at night, but eventual full blind

Question 4

Resting state – in the Dark
gates? Rods and cones? NT, example? Bipolar cells? AP?

In Light
photopigment? activate what?
gates? membrane? bipolars? ganglions? and optic nerve?
—–polarize the rods and cones?

Answer 4

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
HYPERPOLARIZE RODS AND CONES

Question 5

Colour Blindness

Protanopia
Deuteranopia
Tritanopia

Protanomaly
Deuteranomaly
Tritanomaly

how do cones work in response to light

Answer 5

***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

impulses you send are different in the rods and cones. different patterns of actions potentials and the brain can interpret it and say what colour you look at. MEMORY RESPONSE

Question 6

Dark Adaptation
rods or cones?
photopigment? threshold? sensitive? Rods? Vitamins? examples

Light Adaptation
photopigment, reform? effect? sensitive? Example

Answer 6

Dark Adaptation
USING RODS
- Go from light to dark
- Re-form more photopigment. Changes threshold. more likely to give graded potentials
- 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 breakdown of photo-pigment. don’t reform it keeps eyes less sensitive.

• Bleaching
• Eyes become less sensitive with less photopigment
  ***Eg. Walking outside after a movie

Question 7

How are images on the retina

optic chiasma

everything on right and left side of visual field

Answer 7

upside down and backwards
cross over onto the wrong and opposite sides

info crosses over at the optic chiasma. goes to the other side of the brain

everything on left side of FOV, gets processed on the right side.
everything on the right side of FOV, gets processedon the left side