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Unit 19: Biology Part 2 Page 71 of 137
important role in allowing the other
body systems to function.
Eyes and Vision
Try to think of an activity you do,
while you are awake, that does
involve sight. If you are not
visually impaired, this is probably
Figure 55 – Seeing and kicking hard to do. Human beings, more
a soccer ball requires the than many other animals, rely of
sensory division and the their sense of sight to survive.
somatic nervous system, within Sight is our single most important
motor division of the PNS.
sense. For this reason, human
sight is very highly developed.
The autonomic nervous system
is in charge of involuntary motions, As humans, we can see objects
or motions over which you have that are both close up and far
more control. These include such away. We can also tell that they
essential actions as breathing, are close ore far apart because we
digestion, and even the circulation can see in three dimensions. We
of blood. Under normal are able to see in three dimensions
circumstances, the because we have two eyes, both
parasympathetic division of the facing the same direction, a few
autonomic nervous system handles inches apart. So, we see things
all of the necessary involuntary with both our eyes, but from
motions. However, in and slightly different angles. The closer
emergency, the sympathetic an object is to you, the more
division takes over, controlling different the angle from each eye
what is known as the “fight or is. Your brain can use this
flight” response to dangerous or information to see how far apart
frightening situations.
objects are.
As you can see, the nervous Along with being able to see in
system does many things and has three dimensions, humans have
many parts. Consider the chart the ability to see in color. We can
below, which lists the divisions of do this because the eye contains
the system. Each part of the special cells called rods and cones.
system plays a unique and
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