Question

This is a list of some of the steps in the process of seeing a flash of light. Put them in cause-and-effect order from first to last.

A. Photons pass through the ganglion and bipolar cells in the retina
B. Phosphodiesterases break down cyclic GMP
C. A photon is absorbed by a retinal molecule
D. The rod is hyperpolarized
E. Photons are refracted by the lens
F. Transducin molecules bind GTP
G. cGMP-gated Na⁺ channels close
H. Rhodopsin changes shape to its active conformation
I. Photons pass through the cornea
J. Transducin molecules activate phosphodiesterases

Answer 1

Answer )

I) Photons pass through Cornea

E)Photons refracted by Lens

C)Photons absrbed by retinal molecule

A) Photons pass through Retinal and Bipolar cells in Retina .

H)Rhodopsin changes shape to its active configuration

F)Tranduscin bind with GTP

J) Transducin activate Phosphodiesterases

B) Phosphodiestaerase breakdown Cyclic GMP

D) The rod is Hyperpolarized .

Sodium (Na+) channels in the outer segments of the rods and cones are open in the dark, so current flows from the inner to the outer segment. This is known as ‘dark current’.

Current also flows to the synaptic ending of the photoreceptor.

The Na+ – K+ pump in the inner segment maintains ionic equilibrium. Release of synaptic transmitter (glutamate) is steady in the dark .

Phototransduction mechanism

1)First when light falls it enters Cornea ans then through Lens it reaches the Retinal .
Here light is absorbed by retinal molecule and then is passes through Bipolar and Retinal cells in Retina .

2)Retina has rods and cones .Rods for dark vision and cones for Colour vision .

3)When light strikes the outer Segment of Rods ( 11 cis retinal + Opsin) dissociate into All trans Retinal and Opsin separates out .

4)After formation of All trans retinal ,trnasducin get activated by releasing GDP and get converted into activated Transducin with GTP .

5)Activated trabsducin activate Phosphodiesterases enzyme which is responsibe for degradation of Cyclic GMP .

6)Cyclic GMP is responsible for opened Na+ Channels .

7) Separated opsin produces these reactions timately leads to close some of the Na+ channels, and the result is a hyperpolarizing receptor potential.

8)The hyperpolarization reduces the release of Synaptic transmitter and this generates a signal in the bipolar cells that ultimately leads to action potentials in ganglion cells.

9)The action potentials are transmitted to the brain.