Vision Flashcards
What are ommatidia?
Long cylindrical light sensory units in compound eyes
What are the 2 major components of a ommatidium?
A light gathering optical part with an external lens or cornea and a sensory receptor below the optical unit with reticular cells
Why is the cornea immovable?
Because the cornea is continuous with the cuticle
What are reticular cells?
They are cells with many minute neurofibrillae on their surfaces
What do reticular cells do?
Their dendritic extensions form a central, compound, light sensitive rod-like structure called a rhabdom.
What do rhabdom do?
Contain visual pigments called rhodopsin which undergo structural changes in their molecular configuration when illuminated which changes their energy state and relays this to the sensory neurons in the brain.
What does the crystalline cone do?
Funnels light to the rhabdom
What are the primary properties of light?
Intensity and colour
What limits the detail of an image?
The number of ommatidia in the compound eye
What is an apposition image? What causes it?
An image formed when the secondary screening pigment extends down between each ommatidium so the rhabdom is stimulated only by light that enters directly above the lens of the ommatidium - it is common in diurnal insects and used to detect movement
What happens to the ommatidia in dim light?
The secondary screening pigment is contracted and light entering the eye stimulates several ommatidia which superimposes a clear image across numerous reticular cells and these are called ‘clear-zone’ eyes and are more common in nocturnal insects - used to detect changes in intensity of light
What is flicker vision?
The ability to distinguish rapid changes in light over time
Why can the insect eye see successively different images at short intervals?
Because the rhabdoms recover rapidly from the stimulation of light
What receptors occur in what insects?
Green and ultraviolet appear in most insects, blue are usually present in bees and red is generally absent.
