p r o c e ss
diagram
Tracing th e visual p ath w ay from
th e ey e to th e brain • Figure 8.10
PLANNEF
9
Optic nerves
Optic chiasm
Optic
tracts
Thalamus
Right
brain
Impulses travel out of the eyeball
through the optic nerve.
Light
Left'
eye
Right
eye
At the optic chiasm
(point of crossing), half
of the axons from
each eye cross to
the opposite side
of the brain.
Axons from the optic
tract
synapse on
neurons in the
thalamus. These
neurons project to the
primary visual cortex
in the occipital lobe
Left
brain
Uncrossed axon
Crossed axon
Primary
visual areas in the occipital
lobes receive input from both eyes.
Because of the crossing in the optic
chiasm, the following occurs:
• Left side of brain interprets visual
information from right side of an object.
• Right side of brain interprets visual
information from left side of an object.
Signals Travel from the Eye
to the Brain
The action potentials follow a pathway
from the receptor through several neu-
rons into the optic nerves. Along the
way to the brain, the optic nerves cross
at a point called the optic chiasm. In
the
optic chiasm,
some
nerve
fibers
cross to the other side of the brain and
subsequently to the brain’s visual cortex
in the occipital lobe of the cerebrum
(Figure 8.10). There, the impulses are
integrated to form a representative im-
age of the visual field of each eye. Some
information is also relayed to the cer-
ebellum to coordinate eye movements
and balance cues.
1.
How
do tears flow over the
eye?
2.
What
part of the eyeball sup-
plies blood and nutrients?
3.
Which
photoreceptors respond
to colors?
4.
What
is nearsightedness, and
how can it be corrected?
5.
Where
in the brain is visual
information processed?
240 CHAPTER 8
Somatic Senses and Special Senses
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