CHAPTER 1 The Microscope and How It Works 19
type receiving a narrow band of light which largely corresponds to the single
colors
red, green, or blue. The signals received by the cones are transmitted via
the optic nerves to the brain where they are interpreted as color. Color-blind
people are either missing or deficient in one (or more) of these types of cones.
Funny side fact
Plenty of animals beat us out in the color vision department. Many birds, fish
or insects have four types of cones; for example, they can also see ultraviolet
light. To a bumblebee roses may not be so red after all, but full of patterns
which we can’t see.
Structure Function
Cornea Clear window of the eye, covering iris and pupil
Sclera White part of the eye protecting the eyeball
Pupil Opening that allows light to enter into the eye
Iris Colored part, surrounding the pupil, controlling how much light
enters the eye by changing the size of the pupil
Lens Jelly-like structure behind the pupil helping to focus the light onto the
retina
Retina Over 100 million light-sensitive cells detecting light, turning it into
electrical impulses and transmitting messages to the brain
Optic nerves Carry information to the brain for processing
Table 1.1: Having an eye on the eye
Seeing a Human Hair With a Human Eye
When we talk about microscopes and their function we need to keep some size
relations in mind. According to different sources, the smallest object that an average
human can see with the naked eye close up is about 0.1 mm, providing that
your eyes are in a good shape and you have enough light. This is about the size of a
human ovum and definitely smaller than some of the largest protists like amoebas.
0.001 mm 1 m 1,000 nm