Question

12. Write out the sequence of events when light passes through our pupil and ends in acknowledging the object we are viewing. 13. Name and define the stages of processing for our special senses.

Answer 1

12. The sequence of events for a image formation of an object is given below.13. There are basically three stages of processing a vision of an image by the eye.

Light rays in visible wavelength focussed on the retina Activation of photopigment of rods and cones Light induces dissociation of the retinal form opsin resulting in the changes in the structure of the opsin. Membrane permeability of rods and cones changes, Potential difference generated in the photoreceptor cell. It generates action potential in the ganglionic cells through the bipolar cells. Action potentials are transmitted by the optic nerve to the visual cortex of brain. Image formed on the retina is recognised based on earlier memory and experience.

Light adaption or optical stage - During this stage the retina adjust to the various levels of light. The eye quickly adapt to the amount of light available for viewing an object when it falls on the retina.

Retinal stage - In this the falling light on the cones and rods causes changes in their structure which lead to the generation of an action potential. These cells convert the light energy into nerve impluses for processing by the brain.

Neural stage - The nerve impluses generated by the eye is transmitted by the optic nerve to the brain. The main function of the eye is to perceive the light only but its the brain that analyse those signals from optic nerve to form an image of the object that eye is perceiving.