What Is Photo transduction?

It is the process to convert light into electrical signal to understand the visual information by the brain in retina.

 

Fovea contains 1, 50,000 cones/sq.mm., when we focus on any object, image fall at fovea, to deliver information of the object in depth.

There are three types of cell in the retina

1.      Photo Receptor Cell

1.1  Rods Cells: Detects only non-colour light (bright or dark).

1.2  Cone Cells: Detects colours.

2.      Bipolar Cells

3.      Ganglion Cells

Note: Light first strike with the Ganglion cell and then Bipolar cell and the in the last Photo receptors.

 

Light Hyperpolarise the photo receptors, the signal propagate to the bipolar cell to the Retinal Ganglion Cell (RGC) which carries visual information to the brain,

RGC have a receptor field that can be describe two co-centric circles, in circle in the centre and the broader ring around the centre called “Surround” and these receptor field falls into two categories

1.      Off Centre – On Surround

When light on in centre, simulates the RGC fire at a maximum rate

 

 

1.      On Centre – Off Surround.

When light on in centre, simulates the RGC fire at a maximum rate

 

When no light simulates the RGC fire at a base line rate

 

As light circle expand and cover all the Centre and Surround centre, the RGC fire at a base line rate

Inhibition surround can be implemented by lateral inhibition from neighbouring receptor cells. And only main receptor sends the signal to the brain and blocks other receptor by inter-neuron, connected to each other.

There are two type of Lateral Inhibition  

1.      Feed Forward Lateral Inhibition: Neuron may be inhibited by inter neuron as soon as then get signal from receptor cell.

 

2.      Feed Back Lateral Inhibition: Neuron may also inhibit them self in a negative fashion to prevent extra excitement in signal by feeding back signal.