fixing faulty circuits

Question 1

What is a channel rhodopsin ?

Answer 1

light-gated ion channels - non sective to K+,Na+, Ca2+ and H+
stimulate with blue light -480 nm

Question 2

what is halorhodopsin

Answer 2

light-gated ion pump, specific for chloride ions
activated by yellow light
hyperpolarises membrane - so no spiking

Question 3

2 ways to introduce channel rhodopsin and halorhodopsin into the body

Answer 3

• virus to induce expression of channel

- small organic compounds that change channel mechanism

Question 4

how are trans and cis isomers used to effect channels

Answer 4

different light waves cause transformation from trans isomer to cis isomer

e.g if 380nm light causes to become cis, 500nm = trans

the trans isomer may block channel (small current) and cis may not (large current)

Question 5

why may it be beneficial to use a organic compound that can enter the cells

Answer 5

can manipulate channel from the inside without risk of diffusing away, will stay with that cell

Question 6

what is retinitis pigments

Answer 6

disease that effects field of view - becomes smaller over time till blind

photoreceptors, ganglion and bipolar die off over time

Question 7

2 ways to restore vision (theoretically) to patients with retinitis pigmentosa

Answer 7

1. stimulate the visual system in brain - dorsal and ventral stream through opening skull
2. stimulate ganglion cells in retina - easiest to access as they are in front of photoreceptors (first layer)

Question 8

what are the disadvantages of using electrodes to stimulate neurones

Answer 8

if chronic implantation (in permentantly) they can cause cells around to die due to overheating, kill neurones

Question 9

why is stimulation ganglion cells not the best option to cure blindness, what is the solution

Answer 9

they are extremely diverse in function and project to many different areas of the brain

solution - stimulate deeper cells - bipolar or photoreceptors

Question 10

2 types of ganglion cells and their differences

Answer 10

parvocellular - small dendritic tree

magnocellular - large tree

Question 11

explain direction selectivity

Answer 11

only responds to light moving in one direction (specific to e.g. left to right horizontal, not activated if right to left)

Question 12

what is centre surround organisation

why does this occur in ganglion cells

Answer 12

change in the size of spot of light will effect response

peaks at certain diameter and then decreases again if any bigger

occurs because they have inhibitory surrounding receptive field

Question 13

what can halo and channel rhodopsin also be used to treat

Answer 13

seizures