494
UNIT 3
Regulation and Integration of the Body
13
Table 13.2
Cranial Nerves
I Olfactory Nerves
(ol-fak
9
to-re)
Origin and course:
Olfactory nerve fibers arise from
olfactory sensory neurons located in olfactory epithelium
of nasal cavity and pass through cribriform plate of
ethmoid bone to synapse in olfactory bulb. Fibers of
olfactory bulb neurons extend posteriorly as olfactory
tract, which runs beneath frontal lobe to enter cerebral
hemispheres and terminates in primary olfactory cortex.
See also Figure 15.20.
Function:
Purely sensory; carry afferent impulses for
sense of smell.
Clinical testing:
Ask subject to sniff and identify aromatic
substances, such as oil of cloves and vanilla.
Homeostatic Imbalance
Fracture of
ethmoid bone or lesions of olfactory fibers may result
in partial or total loss of smell, a condition known as
anosmia
(an-oz
9
me-ah).
II Optic Nerves
Origin and course:
Fibers arise from retina of eye to form
optic nerve, which passes through optic canal of orbit.
The optic nerves converge to form the optic chiasma
(ki-az
9
mah) where fibers partially cross over, continue
on as optic tracts, enter thalamus, and synapse there.
Thalamic fibers run (as the optic radiation) to occipital
(visual) cortex, where visual interpretation occurs. See
also Figure 15.19.
Function:
Purely sensory; carry afferent impulses for
vision.
Clinical testing:
Assess vision and visual field with eye
chart and by testing the point at which the person first
sees an object (finger) moving into the visual field.
View fundus of eye with ophthalmoscope to detect
papilledema (swelling of optic disc, the site where the
optic nerve leaves the eyeball) and examine optic disc
and retinal blood vessels.
Homeostatic Imbalance
Damage to
optic nerve results in blindness in eye served by nerve.
Damage to visual pathway beyond the optic chiasma
results in partial visual losses. Visual defects are called
anopsias
(ah-nop
9
se-ahz).
Frontal lobe
of cerebral
hemisphere
Olfactory bulb
Olfactory
tract
Cribriform
plate of
ethmoid bone
Filaments of
olfactory
nerve (I)
Nasal mucosa
Eyeball
Retina
Optic nerve (II)
Optic chiasma
Optic tract
Lateral
geniculate
nucleus of
thalamus
Optic
radiation
Visual
cortex
previous page 528 Human Anatomy and Physiology (9th ed ) 2012 read online next page 530 Human Anatomy and Physiology (9th ed ) 2012 read online Home Toggle text on/off