vision

Question 1

what is rodopsin composed of?

Answer 1

Rodopin composed of an opsin and a retinal GPCR

Question 2

how does Rodopsin function

Answer 2

When light interacts with opsins it changes structure of opsin from trans to cis isomer de-activating the transducin GPCR

Question 3

explain the different types of visual states

Answer 3

Photopic vision datlight cones only used
Mesotopic vision -twightlight mixture of both rod and cones
Scotopic vision- rods only used

Question 4

how is light and dark adaption achived?

Answer 4

Light adaptation -pupil constriction, shift from rod to cone function, resynthesis of photopsin
Dark adaptation- pupil dilation, shift from cone to rod vision, resynthesis of rodopsin

Question 5

approximately how much cortical space does vision take up?

Answer 5

1/3

Question 6

what is myopia

Answer 6

Myopia- short sightedness

Question 7

what is hypermetropia?

Answer 7

farsightedness

Question 8

what is Astigmatism

Answer 8

rugby ball shaped cornea

Question 9

roughly how many rods cones and retinal ganglion cells do we have per retina?

Answer 9

125m rods
7m cones
1m retinal ganglion cells

Question 10

where are graded potentials used?

Answer 10

Graded potentials are used for all the pre ganglionic cells

Question 11

what role do amacrine cells play?

Answer 11

have a central role in cone and rod pathways linking pathways via gap junctions so in mesopic light cone signals can be boosted by rod detection.

Question 12

explain photo transduction in rods and cones

Answer 12

1) light induces a con change in rodopsin/photopsin cis–> trans activating transductin the G protine
2) g protine subunits then activate cGMP Phosphodiesterase (PDE)
3) PDE reduces the concentration of cGMP leading to closure of Na+ channels and hyperpolarisation of the cell ~35mV–>65mV

Question 13

state the function of horizontal cells in the retina

Answer 13

Horizontal cells in the retina connect peripheral photoreceptors to central photoreceptors by inhibitory GABA ergic synapses creating center surround antagonism

Question 14

what is the difference between on and off bipolar cells?

Answer 14

ON and off bipolar cells express different Glutamate receptors on their dendrites
Off bipolar express AMPA opens cation channel prevents hyperpolarisation
On bipolar cell expresses mGluR6 glutamate binding closes cation channel hyperpolarizes for graded response

Question 15

explain types and percentages of ganglion cells

Answer 15

90% P(parvocellular) type historically called midget cells due to dendritic tree , pick up colour and contrast better
5% M (Magnocellular) -parasol cells due to broad dendritic trees only pick up black and white, low contrast, highly sensitive to rapidly changing stimulus. In lower order animals they are movement sensitive cells but not in humans
Non M/Non-P cells (5% Koniocellular, or K pathway; can be called Bistratified cells) – less well characterized, many subtypes Photosensitive ganglion cells
(i) contain the photopigment melanopsin, projected to the SCN via the retinohypothalamic tract, involved in setting and maintaining circadian rhythms.

Question 16

Why is V1 considered v1? what do lessions create?

Answer 16

Most of the lgn neurons terminate here, all cells are exited by vision, lesions create absence of conscious vision

Question 17

what does damage to magnocellular and parvocellular LGN create deficits in?

Answer 17

Damage to magnocellular LGN - sharp reduction in the ability to perceive rapidly changing stimuli.
No effect on visual acuity or colour vision.

Damage to parvocellular LGN – no effect on motion perception, but severely impairs visual acuity
and chromatic perception.

Conclusion : Parvocellular stream is important for high spatial resolution – size, shape and colour of
objects. Magnocellular stream is critical for tasks that require high temporal resolution – location,
speed and direction of a rapidly moving object

Question 18

in V1 what is significant about the orientation of lines cells will respond to in a column?

Answer 18

will all be parallel and adjacent columns will show slight rotation

Question 19

what is significant about cortical blobs in V1 and how can they be imaged

Answer 19

Blobs can be stained using cytochrome oxidase a mitochondrial enzyme
Blobs are primarily concerned with colour
Cells in blobs can be both single and double opponents.