Neuroanatomy Draw It To Know It

390 Neuroanatomy: Draw It to Know It

Visual Pathways: Axial View

Here, we will draw an axial view of the visual pathways
from the retinae to the occipital cortices. We will show
only the right visual fi eld projection to the left visual
cortex for simplicity — the left visual fi eld projects to the
right visual cortex in mirror-image fashion. First, let’s
address the visual fi elds: the visual fi elds represent the
person’s view of the world. Draw axial sections through
the left and right eyes and draw projections from central
vision to the fovea of each eye. Using the fovea as the
midpoint of the retina, subdivide the retinae into nasal
and temporal hemiretinae. Now, we are ready to march
through the optic projections from the right visual fi eld
to the left visual cortex.
First, show that the right visual fi eld projects to the
temporal left hemiretina and the nasal right hemiretina.
Next, let’s establish the key structures along the path of
the optic projections. Draw the optic chiasm, the lateral
geniculate nuclei, and the visual cortices. Indicate that

the left visual cortex receives the right visual fi eld and

that the right visual cortex receives the left visual fi eld.

Now, show that the left temporal hemiretina projects

ipsilaterally to the left lateral geniculate nucleus, and

then, show that the right nasal hemiretina sends crossing

fi bers through the optic chiasm to the contralateral lat-

eral geniculate nucleus (the left lateral geniculate

nucleus). Finally, show that the left lateral geniculate

nucleus sends optic radiations to the left occipital cortex.

We have now completed the path from the right visual

fi eld to the left visual cortex.

Next, let’s defi ne the optic nerve and optic tract.

Encircle the optic projection between the retina and

the chiasm and label it as the optic nerve, and encircle

the projection between the optic chiasm and the lateral

geniculate nucleus and label it as the optic tract. Optic

nerve injuries are prechiasmatic and optic tract injuries

are postchiasmatic.

Temporal pole

Anterior commissure

Lateralgeniculate

nucleus

Optic radiations

Primary visual area(occipital lobe)

Medial geniculatenucleus

Crus cerebri

Optic chiasmaOptic tract

Olfactory tract

Optic nerve (CN II)

FIGURE 22-1 Axial view of optic pathway. Used with permission from Bruni, J. E. & Montemurro, D. G. Human Neuroanatomy: A Text, Brain Atlas,
and Laboratory Dissection Guide. New York: Oxford University Press, 2009.