Physiology Of Vision II

Question 1

What are Visual pigments ?

Answer 1

Disc’s of outer segment in both rods and cones contain this pigment and this is where light absorption occurs and is a derivative of rhodopsin

Question 2

What are the 3 types of cones?

Answer 2

Red
Green
Blue

Question 3

What is colour blindness?

Answer 3

Inability to distinguish colours
When one or more classes of cones are non-functional and unable to manufacture necessary visual pigments

Question 4

What is Photoreception?

Answer 4

It begins when photon hits the retinal portion of a rhodopsin molecule that’s in membrane of disc the opinion is activated

Question 5

What are the 2 possible configurations of Bound retinal molecule?

Answer 5

11 cis firm and 11 trans form

Question 6

What happens to the 11 cis form?

Answer 6

When it absorbs light it changes to a more linear 11 trans form this then activates opsin molecule

Question 7

What is Transducin?

Answer 7

It is a G proteins a membrane bound enzyme complex

Question 8

How is transducin activated?

Answer 8

It is activated by opsin and transducin will activate PDE

Question 9

What is PDE?

Answer 9

It is an enzulyme that breaks down cGMP and the levels decline and gated Na close

Question 10

How are the Na channels inactivated?

Answer 10

When cGMP is removed and this will the decrease Na entry into cytoplasm

Question 11

What happens at -40Mv during photoreception?

Answer 11

Photoreceptors are continously releasing NT (glutamate) across synapses at the inner segment and Na is constantly being pumped out

Question 12

What is dark current?

Answer 12

The constant movement of Na from outer segment to inner segment and out of cell

Question 13

What happens when Na channels close?

Answer 13

The transmembrane potential drops towards-70MV and reduction of Na entry will reduce dark current because the active transport continues to move Na from cytoplasm

Question 14

What happens when membrane hyperpolarizes?

Answer 14

The rate of glutamate release will decrease and this will cause Na channels on bipolar cells to open indicating to the adjacent bipolar cell that the photoreceptir has absorbed the photon

Question 15

What is bleaching?

Answer 15

After absorbing the photon the retinal does not revert the 11 cis form the entire rhodopsin breaks down into retinal and opsin and reassemble before it revombine with opsin retinal enzymatically converts 11 cis form

Question 16

What us the cause of night blindness?

Answer 16

Lack of vit A because Vit A is a source of retinin

Question 17

What us the Dark adapted state?

Answer 17

After 30 min or more being in the dark the visual pigments will have recovered from photo bleaching and fully receptive to stimulation

Question 18

What are ganglion cells?

Answer 18

They monitor a specific portion of the visual field and are made of two types M and P cells

Question 19

What are M cells?

Answer 19

They monitor the rod and are really big they provide information on motion,depth perception,location of objects and general form of object

Question 20

What are P cells?

Answer 20

They monitor the cones and are much smaller provide information about edges,colour and fine detail

Question 21

What are on center neurons?

Answer 21

Excited by light arriving in center and inhibited when light strikes edges of receptive field

Question 22

What are off center neurons?

Answer 22

Inhibited by light in central zone and are stimulated by illumination at edges

Question 23

What are visual pathways?

Answer 23

They begin at photoreceptors
And end at visual cortex of cerebral hemispheres
Message crosses two synapses before it heads towards brain

Question 24

What are the two synapses of visual pathways?

Answer 24

Photoreceptor to bipolar cell
Bipolar cell to ganglion cell

Question 25

What are the central pathways of visual information?

Answer 25

Axons from ganglion cells converge on optic disc and penerate wall of eye and more to the diencephalon as optic nerve 2 the two optic nerves reach duencephalon at optic chiasm

Question 26

What us visual data?

Answer 26

It is the combined field of vision that arrives at visual cortex of opposite occipital lobe
Left half at right occipital lobe
Right half at left

Question 27

Want is optic radiation?

Answer 27

A bundle of projection fibers that link lateral geniculate with visual cortex