Page 533 - Fundamentals of anatomy physiology

The Optic Nerves (II) The reorganized axons continue toward the lateral geniculate
nuclei of the thalamus as the optic tracts (Figures 14–19 and
Primary function: Special sensory (vision) 14–21). After synapsing in the lateral geniculates, projection
fibers deliver the information to the visual cortex of the occipital
Origin: Retina of eye lobes. With this arrangement, each cerebral hemisphere receives
visual information from the lateral half of the retina of the eye
Pass through: Optic canals of sphenoid p. 243 on that side and from the medial half of the retina of the eye of
the opposite side (Figure 14–17). A few axons in the optic tracts
Destination: Diencephalon by way of the optic chiasm bypass the lateral geniculate nuclei and synapse in the superior
colliculi of the midbrain. We will consider that pathway in
The optic nerves (II) carry visual information from special sen- Chapter 17.
sory ganglia in the eyes (Figure 14–21). These nerves contain
about 1 million sensory nerve fibers. The optic nerves pass The Oculomotor Nerves (III)
through the optic canals of the sphenoid. Then they converge
at the ventral, anterior margin of the diencephalon, at the optic Primary function: Motor (eye movements)
chiasm (chiasma, a crossing). At the optic chiasm, fibers from
the medial half of each retina cross over to the opposite side of Origin: Midbrain
the brain.
Pass through: Superior orbital fissures of sphenoid pp. 237,
Figure 14–21 The Optic Nerve. 244, 246, 249

Pituitary Eye Destination: Somatic motor: superior, inferior, and medial rectus
gland Olfactory bulb muscles; inferior oblique muscle; levator palpebrae superioris
Olfactory tract muscle. Visceral motor: intrinsic eye muscles
Optic nerve
(N II) The midbrain contains the motor nuclei controlling the third and
Optic chiasm fourth cranial nerves. Each oculomotor nerve (III) innervates
four of the six extrinsic muscles that move the eye, and the leva-
Optic tract tor palpebrae superioris muscle, which raises the upper eyelid
(Figure 14–22). On each side of the brain, nerve III emerges from
Lateral the ventral surface of the midbrain and penetrates the poste-
geniculate rior wall of the orbit at the superior orbital fissure. Individuals
nucleus (in with damage to this nerve often complain of pain over the eye,
thalamus) droopy eyelids, and double vision, because the movements of
the left and right eyes cannot be coordinated properly.

The oculomotor nerve also delivers preganglionic autonomic
fibers to neurons of the ciliary ganglion. These neurons control
intrinsic eye muscles. These muscles change the diameter of the
pupil, adjusting the amount of light entering the eye. They also
change the shape of the lens to focus images on the retina.

Midbrain Visual cortex Optic projection
(cut) (in occipital lobes) fibers

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