BMS11004 WEEK 8 - WEDNESDAY

Question 1

name rod photopigment

Answer 1

rhodopsin

Question 2

give 2 parts of rhodopsin (rod photopigment), with their roles

Answer 2

retinol- absorb light, change config
opsin- confirmational change due t retinol shape change
shape change causes rhodopsin to act differently with GPCR

Question 3

name cone photopigment

Answer 3

3 types of opsin (S, M, L)

Question 4

what is retinal ganglion photopigment

Answer 4

melanopsin

Question 5

when are photoreceptor hyperpolarise/depolarised

Answer 5

hyperpolarised by light
depolarised at rest

Question 6

describe phototransduction

Answer 6

in dark lots of cGMP bind to channels in photoreceptor membranes
cGMP-gated channel is non-selective cation
open in dark, allow Na influx into photorec “dark current”
to prevent overdepolarisation, K leave cell, regulates MP
light reduces cGMP levels, closing channel, prevent Na influx leading to hyperpolarisation of photoreceptors

Question 7

explain how cGMP is a ligand in phototransduction

Answer 7

cGMP is ligand for channel
if less cGMP, more channel shut, less Na enter, but K still leaving causes hyperpolarisations

Question 8

how many photons evokes sensations of light in humans

Answer 8

5-7

Question 9

how is rhodopsin used in phototransduction

Answer 9

activated by light and stimulate G-protein transduction, to become transduction GTP
activate enzyme PDE, reducing cGMP levels, closing Na channels
signal amplification due to enzyme cascade

Question 10

explain differences in rods and cones when saturated with bright light

Answer 10

rods cannot process bright lights= becomes easily saturated
rhodopsin is bleacher, cGMP level so low that no extra hyperpolarisation
cone not easily saturated, so used in bright light

Question 11

what ion is required for light adaptations

Answer 11

calcium

Question 12

in dark, how does calcium impact phototransduction

Answer 12

Ca enter cells via nonselective cation channel, blocking guanylyl cyclase and reducing cGMP production so close some ion channel
keep cGMP levels steady in dark

Question 13

in light, how does Ca work alongside phototransduction

Answer 13

channel shut, so Ca cant enter
releases blocked guanylyl cyclase
so increase cGMP production meaning more channels open and sodium, calcium enter

Question 14

provide summary of phototransduction

Answer 14

Na enter via cGMP-dependent non-selective cation channel “dark current”, causes photoreceptor depolarisation in dark
photons activate photopigment, causing cGMP breakdown
Ca mediates adaption to continued light stimulation

Question 15

explain why bipolar cells are not just relay cells

Answer 15

downstream of photoreceptor bypasses bipolar cells
bipolar cell also integrates and processes info
when light enters, increase glutamate crossing so bipolar cell can send info to retinal ganglion cell

Question 16

what are 2 type of bipolar cells

Answer 16

on, off

Question 17

outline on bipolar cells

Answer 17

more glutamate to bind to receptor so more response meaning bipolar cells depolarise (in dark)

Question 18

what type of receptor do on bipolar cell express

Answer 18

ionotropic glutamate receptors that can be inhibitory

Question 19

what are off bipolar cells

Answer 19

less glutamate to bind to receptors so less response meaning bipolar cells hyperpolarise (light)

Question 20

what receptors do off bipol cells express

Answer 20

metabotropic glutamate receptors

Question 21

photoreceptor hyperpolarises to light which reduces glutamate release. if bipolar cell hyperpolarises, what type is it

Answer 21

off bipolar cell

Question 22

photoreceptor hyperpolarises to light which reduces glutamate release. if bipolar cell depolarises, what type is it

Answer 22

on bipolar cell

Question 23

what eye parts have increased focused receptive-field

Answer 23

fovea