7th Grade Science Student ebook

UNIT 5 STRUCTURE AND FUNCTION IN LIVING THINGS

Figure 15.26: The mammalian eye.

cornea - part of the eye that,

along with the lens, refracts and

focuses light.

retina - a thin layer of cells in the

back of the eye that converts light

into nerve signals.

optic nerve - a nerve that

transmits signals from the eye

to the brain.

The mammalian brain and eye

The central

nervous system

The brain of a mammal is more developed than that of other

vertebrates. One difference is that mammals have a larger

cerebrum and cerebellum, as shown below. The cerebrum is the

part of the brain where most thinking takes place. The cerebellum

coordinates movement and balance. Their well-developed brains

allow mammals to think, learn, and quickly respond to changes in

their environment.

The mammalian

eye

Vision is an important way mammals perceive their environment.

Figure 15.26 shows the structures of the mammalian eye. The lens

is a transparent structure that, along with the cornea, refracts

and focuses light. The pupil is a hole in the iris that controls the

amount of light entering the eye. The iris is the pigmented part of

the eye. A ring of tiny ciliary muscles connects the lens to the inner

surface of the iris. Ciliary muscles contract to change the shape of

the lens. The retina is a thin layer of cells in the back of the eye

that converts light into nerve signals. Those signals are

transmitted to the brain by the optic nerve. The sclera is the

protective outer layer that gives the eye its shape. The chroroid

provides oxygen and nutrients to the retina. The eye is filled with

a jelly-like substance called vitreous and aqueous humor. External

muscles control eye movement and help focus images.