The retina – the light detector of the eye, Physics

The retina – the light detector of the eye:


The physical aspects of the retina:
1.The absorption of a light photons in a photoreceptor triggers an electrical signal to the brain-an action potential fig(4).
2. The energy of the photon is about 3 eV: the action potential has an energy millions of times greater.
3. The light photons apparently causes a photo chemical reaction in the photoreceptor which in some way initiates the action potential.
4.the photon must be above the minimum energy to cause the reaction.

 

1583_The retina – the light detector of the eye.png



The image on the retina is very small .A convenient equation for determining the size of the image on the retina comes from the ratios of the lengths of the sides of similar triangle fig (4).


O/P=I/Q


Where O is the object size ,I the image size ,P the object distant and Q the image distance usually about 2 cm. Fig(5)

 

1132_The retina – the light detector of the eye 2.png


There are two photoreceptor in the retina:

The cones and the rods .Though out most of the retina cones and rods are not on the surface of the retina but lie behind several layers of nerve tissue through which the light must pass fig(6) The rods and cones distributed symmetrically in all directions from the visual axis except in one region- the blind spot.

 

269_The retina – the light detector of the eye 3.png


-The rods are used for night or scayopic vision and for peripheral vision, they are much more abundant than the cones(~120 million in each eye).
- The rods are most sensitive to blue- green light(~510 nm).

The blind spot: It is a region from about 13o to 18o  that has neither cones nor rods ,this is the point at which the optic nerve.


-The cones (~ 6.5 million in each eye),they are primarily used in day light or photopic vision.
- With cones we can see fine details  and recognize deferent colors.
- The cones are not uniformly sensitive to all colors but have maximum sensitivity at about 550 nm in the yellow- green region .

Posted Date: 10/1/2012 8:42:20 AM | Location : United States







Related Discussions:- The retina – the light detector of the eye, Assignment Help, Ask Question on The retina – the light detector of the eye, Get Answer, Expert's Help, The retina – the light detector of the eye Discussions

Write discussion on The retina – the light detector of the eye
Your posts are moderated
Related Questions
Q. State the fundamental postulates of special theory of relativity? The two basic postulates of the special theory of relativity are: (i) The laws of Physics are the simila

what is dynamics

what is gravitational field is?

what multiplication fact can be found by using the arrays or 2times9 and 5times9?

measurement and calculation with formula

The index of refraction of a particular medium is nearly the same for all wavelengths hence we often associate a single value the average value of the index of refraction to the me

Trying to make an interesting pattern, an artist slowly pours 1.00 cm 3 of liquid gold onto a large block of ice at 0.00°C. While being poured, the liquid gold is at its melt

In the circuit shown in Figure, with the switch in position 1, the capacitor is uncharged. If he switch is moved to position 2 at time t =0s, measure (i) The initial curren

What are the units of fibre optic communication system? Fibre Optic Communication System: This comprises of the given three most important units: a. Transmitter: It has i

1]What is the difference between a photon and a neutron? 2]Why are they massless?