NBIO 401
Fall 2013
Cranial Nerves
Class 7 – Wednesday, October 9, 2013
Robinson
Objectives:
-Be able to describe the position at which each cranial nerve exits the brainstem.
-Be able to summarize the sensory and motor information that travels in each cranial nerve.
As we learned at the start of our study of cranial nerves, there is not a one-to-one
correspondence between cranial nerve nuclei and the cranial nerves that connect these
nuclei to structures outside the brainstem.
To review:
-Cranial nerve nuclei are either sensory or motor.
Sensory nuclei (e.g., the main sensory nucleus of the trigeminal) receive sensory
information from peripheral receptors in the head. These nuclei are analogous
to the neurons in the spinal cord that receive sensory information from
receptors in the body.
Motor nuclei (the motor trigeminal nucleus) contain the motoneurons of the
striated in the head and the preganglionic neurons for smooth muscles and
glands in the head and also the thorax and abdomen.
IN CONTRAST
-Cranial nerves are bundles of axons traveling into (sensory) or out of (motor) the
brainstem. A single cranial nerve can contain only sensory axons (carrying information to
sensory cranial nerve nuclei), only motor axons (carrying motor output signals), or both.
Today we will describe each cranial nerve, from III (oculomotor) to XII (hypoglossal).
For each nerve we will describe, and you should learn:
1) where it exits the brainstem
2) its components, i.e., what axons it contains.
(For each nerve there is also a drawing showing the course of the nerve from the brain
to the periphery. These drawings are interesting and help visualize where the nerve leaves
the brainstem. The rest of the pathway from the brain to the periphery may prove useful to
you in the future but for NBIO 401 you will not have to reproduce this pathway.)
-Class 7 page 1-
NBIO 401
Fall 2013
CRANIAL NERVE III - OCULOMOTOR
LOCATION
The oculomotor (IIIrd) nerve emerges from the ventral side of the midbrain near the
midline just rostral of the pons.
COMPONENTS
The oculomotor (IIIrd) nerve contains somatic motor (GSE) axons that innervate 4 of the 6
extraocular muscles, i.e., the medial, superior and inferior rectus muscles, and the inferior
oblique muscle . The cell bodies for these axons are in the oculomotor nucleus. We will
learn more about extraocular muscles in the Oculomotor Anatomy lecture on October 31.
The IIIrd nerve also contains visceral motor (GVE) axons that terminate on the ganglionic
neurons that constrict the pupil. The cell bodies for these fibers are in the Edinger-Westphal
nucleus dorsal and rostral to the oculomotor nucleus.
The chart and drawing on the next page summarize this information.
-Class 7 page 2-
NBIO 401
Fall 2013
-Class 7 page 3-
NBIO 401
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CRANIAL NERVE IV - TROCHLEAR
LOCATION
The trochlear (IVth) nerve emerges from the dorsal side of the brainstem on the rostral
edge of the inferior colliculus. The axons cross the midline, wrap around the brainstem just
rostral of the pons and course away from the brainstem once they are on the ventral side of
the brainstem. The IVth nerve is the only cranial nerve to exit the dorsal surface of the
brainstem and the only cranial nerve that completely crosses the midline.
COMPONENTS
The trochlear (IVth) nerve contains somatic motor (GSE) axons that innervate one of the
extraocular muscles not supplied by the IIIrd nerve, the superior oblique muscle. The cell
bodies of these axons are in the trochlear nucleus just caudal to the oculomotor nucleus.
-Class 7 page 4-
NBIO 401
Fall 2013
-Class 7 page 5-
NBIO 401
Fall 2013
CRANIAL NERVE V - TRIGEMINAL
LOCATION
The trigeminal (Vth) nerve exits the lateral edge of the brainstem directly in the rostralcaudal middle of the pons. It is a good landmark for the approximate rostral-caudal middle of
the pons.
COMPONENTS
The trigeminal (Vth) nerve contains 2 components. 1) Branchial motor (SVE) axons that
innervate the muscles of mastication. As the chart on the next page says, Vth nerve motor
axons also innervate several other muscles. In NBIO 401 we will focus only on the muscles
of mastication. 2) General sensory (GSA) axons carrying sensory information from specific
regions of the head into the main sensory trigeminal nucleus (analogous to the dorsal column
nuclei – conscious touch and proprioception), the spinal trigeminal nucleus (analogous to the
dorsal horn of the cord - pain) and the mesencephalic nucleus of the trigeminal (analogous to
the external cuneate nucleus and Clarke’s Column – unconscious proprioception). The chart
and the drawing on the next page summarize this information.
-Class 7 page 6-
NBIO 401
Fall 2013
-Class 7 page 7-
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Fall 2013
To the right we see the
three dermatomes of the
trigeminal nerve. The
top one (called V1)
sends information into
the brainstem via the
ophthalmic division of
the Vth nerve. The next
one (called V2) sends
information into the
brainstem via the
maxillary division of the
Vth nerve. The bottom
dermatome (called V3)
sends information into
the brainstem via the
mandibular division of
the Vth nerve.
To the left we see a review
of the locations and extents of
the 4 nuclei that either receive
input from the trigeminal nerve
(the mesencephalic nucleus;
the main sensory nucleus,
called the pontine trigeminal
nucleus here; the spinal
trigeminal nucleus) or send
motor axons out via the
trigeminal nerve (the motor
trigeminal nucleus, here called
the masticator nucleus.)
-Class 7 page 8-
NBIO 401
Fall 2013
CRANIAL NERVE VI - ABDUCENS
LOCATION
The abducens (VIth) nerve exits the ventral side of the brainstem several millimeters
lateral of the midline in the crease between the pons (rostrally) and the medulla (caudally).
COMPONENTS
The abducens (VIth) nerve contains only 1 type of axon, somatic motor (GSE) axons that
innervate the lateral rectus muscle, the one extraocular muscle not innervated by the IIIrd or
IVth nerves. The cell bodies of these axons are in the abducens nucleus.
The chart and drawing on the next page summarize this information.
-Class 7 page 9-
NBIO 401
Fall 2013
-Class 7 page 10-
NBIO 401
Fall 2013
CRANIAL NERVE VII - FACIAL
LOCATION
The facial (VIIth) nerve exits the ventral side of the brainstem in the crease between the
pons (rostrally) and the medulla (caudally) lateral to the abducens nerve but medial to the
auditory/vestibular (VIIIth) nerve. That is, the VIIth nerve is in the middle of the 3 nerves that
come out of the ponto-medullary junction on each side.
COMPONENTS
The VIIth nerve contains 4 components. 1) Branchial motor (SVE) axons that innervate
the muscles of facial expression as well as several other muscles that we will not worry about
for NBIO 401. The motoneurons for these fibers are in the facial nucleus. 2) Visceral motor
(GVE) axons that innervate the ganglion that drives salivation in several salivary glands. The
cell bodies of these neurons are in the superior salivatory nucleus. 3) General sensory
afferent (GSA) axons that carry touch information from the skin on part of the ear. 4) Special
visceral afferent (SVA) axons that bring taste information from the anterior 2/3 of the tongue
to the rostral solitary nucleus.
The chart and drawing on the next page summarize this information.
-Class 7 page 11-
NBIO 401
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-Class 7 page 12-
NBIO 401
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To the left we
see the pathway
from the
hypothalamus, to
the superior
salivatory
nucleus, to
peripheral
ganglia and
finally to salivary
glands.
To the right we see the pathway from
the anterior 2/3 of the tongue to the
solitary nucleus, thalamus, and finally
the taste region of the cerebral
cortex.
-Class 7 page 13-
NBIO 401
Fall 2013
Above we see the components of the facial nerve and the facial intermediate nerve. The
facial nerve contains all of the components described above. The facial intermediate nerve
contains the subset consisting of every type of axon except the motor fibers to the muscles of
facial expression (YELLOW).
Thus the facial intermediate nerve contains axons carrying:
1 – (ORANGE) output from the superior salivatory nucleus that, via a neuron in a peripheral
ganglion, drive several salivary glands to produce saliva
2 – (GREEN) taste information from the anterior 2/3 of the tongue to the rostral half of the
solitary nucleus
3 - (BLUE) somatosensory information form the outside of the ear to the spinal trigeminal
nucleus
-Class 7 page 14-
NBIO 401
Fall 2013
CRANIAL NERVE VIII – AUDITORY/VESTIBULAR
LOCATION
The VIIIth nerve is the most lateral cranial nerve to exit the brainstem at the junction
between the pons (rostrally) and the medulla (caudally).
COMPONENTS
The VIIIth nerve contains axons carrying two distinct types of sensory information,
auditory and vestibular. The cell bodies of auditory axons are in the spiral ganglion in the
cochlea. Those for the vestibular axons are in the vestibular ganglion also called Scarpa’s
ganglion.
The chart and drawing on the next page summarize this information.
-Class 7 page 15-
NBIO 401
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Below we see the auditory pathway from the cochlea via the VIIIth nerve to the dorsal and
ventral cochlear nuclei, superior olivary nucleus, inferior colliculus, thalamus, and finally the
auditory cortex.
-Class 7 page 16-
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Below we see the vestibular pathway from the peripheral vestibular apparatus, the
semicircular canals and otoliths, together called the labyrinth, via the VIIIth nerve to the 4
vestibular nuclei. The nuclei, in turn, project rostrally and caudally. The rostral projection
goes to the IIIrd, IVth & VIth nuclei that contain the motoneurons for the extraocular muscles.
The caudal projection goes to the spinal cord. There is also a small projection from the
vestibular nuclei to the thalamus (not shown) and then from the thalamus to the vestibular
part of the cerebral cortex to provide conscious awareness of vestibular stimulation.
-Class 7 page 17-
NBIO 401
Fall 2013
CRANIAL NERVE IX – GLOSSOPHARYNGEAL
LOCATION
The IXth nerve exits the lateral side of the rostral medulla just behind the medulla’s
junction with the pons. Several small rootlets are arrayed rostral to caudal in a small region.
COMPONENTS
The IXth nerve has 5 components. 1) Branchial motor axons (SVE) connecting
motoneurons in the nucleus ambiguus to muscles of the pharynx and larynx. 2) Visceral
motor (GVE) axons from the inferior salivatory nucleus to a peripheral ganglion that drives a
salivary gland. 3) Visceral sensory (GVA) axons from the carotid body to the posterior half of
the solitary nucleus. (Carotid body is group of receptor cells at the bifurcation of the carotid
artery that senses blood CO2, O2, pH, & temperature.) 4) Somatosensory (GSA) axons
carrying touch & pain information from the posterior 1/3 of the tongue and the inside of the
ear to the spinal trigeminal nucleus. 5) Taste (SVA) axons carrying taste information from the
posterior 1/3 of the tongue to the rostral half of the solitary nucleus.
The chart and drawing on the next page summarize this information.
-Class 7 page 18-
NBIO 401
Fall 2013
Below we see a close up view of the IXth nerve showing its 5 components.
1 – (YELLOW) branchial motor axons from motoneurons in the nucleus ambiguus to muscles
of the pharynx and larynx
2 – (ORANGE) visceral motor axons from the inferior salivatory nucleus to a peripheral
ganglion that drives a salivary gland
3 – (PURPLE) visceral sensory axons from the carotid body to the posterior half of the solitary
nucleus
4 – (BLUE) axons carrying touch & pain information from the posterior 1/3 of the tongue and
the inside of the ear to the spinal trigeminal nucleus
5 - (GREEN) axons carrying taste information from the posterior 1/3 of the tongue to the rostral
half of the solitary nucleus
-Class 7 page 19-
NBIO 401
Fall 2013
Above we see a lower power summary of the 5 components of the IXth nerve.
-Class 7 page 20-
NBIO 401
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The drawing to the left
shows the pathway from the
motor cortex to the nucleus
ambiguus and then, via the
IXth nerve, to muscles of
the larynx and pharynx.
The drawing to the right shows
the typical parasympathetic
pathway from the hypothalamus
to the inferior salivatory nucleus,
and then via the IXth nerve to a
peripheral parasympathetic
ganglion, to a salivary gland.
-Class 7 page 21-
NBIO 401
Fall 2013
The drawing to the
left shows the
pathway from the
carotid body via
the IXth nerve to
the posterior half of
the solitary
nucleus.
The drawing to
the right shows the
somatosensory
pathway from the
posterior 1/3 of the
tongue via the IXth
nerve to the spinal
trigeminal nucleus.
-Class 7 page 22-
NBIO 401
Fall 2013
The drawing above shows the pathway from the taste receptors on the posterior 1/3 of the
tongue via the IXth nerve to the rostral half of the solitary nucleus, which in turn projects to
the thalamus which projects to the taste region of the cerebral cortex.
-Class 7 page 23-
NBIO 401
Fall 2013
CRANIAL NERVE X - VAGUS
LOCATION
The vagus (Xth) nerve exits the lateral side of the medulla caudal to the IXth nerve. It
consists of a group of rootlets spread out over a small rostral-caudal region. The caudal part
of the Xth nerve is about even with the caudal end of the inferior olivary bulge.
COMPONENTS
The Xth nerve has 4 components. 1) Branchial motor (SVE) axons from motoneurons in
the nucleus ambiguus to muscles of the larynx and pharynx. 2) Visceral motor (GVE) axons
from the dorsal motor nucleus of the vagus (DMX) to parasympathetic ganglia in the larynx,
pharynx, thorax and abdomen that drive smooth muscle and glands. 3) Visceral sensory
(GVA) axons from the trachea, esophagus, thoracic and abdominal viscera, and aorta to the
caudal half of the solitary nucleus. 4) Somatosensory (GSA) axons carrying touch and pain
information from the outside of the ear and the pharynx to the spinal trigeminal nucleus.
The chart on the next page summarizes this information.
-Class 7 page 24-
NBIO 401
Fall 2013
-Class 7 page 25-
NBIO 401
Fall 2013
Below we see the Xth nerve showing its 4 components.
1 – (YELLOW) branchial motor axons from motoneurons in the nucleus ambiguus to muscles
of the pharynx and larynx
2 – (ORANGE) visceral motor axons from the dorsal motor nucleus of the vagus to peripheral
parasympathetic ganglia that drive smooth muscles and glands in the pharynx, larynx, thorax
and abdomen.
3 – (PURPLE) visceral sensory axons from the trachea, esophagus, thoracic and abdominal
viscera, and aorta to the caudal half of the solitary nucleus; there is also a small projection
(not shown but you need to know it) from taste buds on the epiglottis to the rostral half of the
solitary nucleus
4 – (BLUE) axons carrying touch & pain information from outside of the ear and the pharynx to
the spinal trigeminal nucleus
-Class 7 page 26-
NBIO 401
Fall 2013
The drawing above shows the pathway from the motor cortex to the ambiguus nucleus
which projects via the Xth nerve to muscles of the larynx and pharynx.
-Class 7 page 27-
NBIO 401
Fall 2013
The drawing above shows the pathway from the dorsal motor nucleus of the vagus (DMX) via
the Xth nerve to parasympathetic ganglia in the neck, thorax, and abdomen. Here the
ganglia are not shown but are at the ends of the orange nerves exiting the Xth nerve.
-Class 7 page 28-
NBIO 401
Fall 2013
The drawing above shows the pathway carrying sensory information from the viscera of the
abdomen, thorax, and throat via the Xth nerve to the caudal half of the solitary nucleus.
Again, there is also a small projection (not shown below but you need to know it) from taste
buds on the epiglottis to the rostral half of the solitary nucleus
-Class 7 page 29-
NBIO 401
Fall 2013
This drawing shows the pathway of somatosensory axons from the neck and ear via the
Xth nerve to the spinal trigeminal nucleus.
-Class 7 page 30-
NBIO 401
Fall 2013
CRANIAL NERVE XI – SPINAL ACCESSORY
LOCATION
Axons of the spinal accessory (XIth) nerve originate from neurons in the accessory
nucleus in the upper spinal cord. They travel rostrally through the foramen magnum and then
turn laterally to course away from the lateral side of the caudal medulla. This bundle is called
the “spinal part” of the XIth nerve. Some authors also identify a “cranial part” that consists of
axons originating from cells in the caudal ambiguus nucleus. You can see the cranial part of
the XIth nerve in the drawing below. In NBIO 401 we will not include the “cranial part” as part
of the XIth nerve. Here the XIth nerve consists only of axons originating in the spinal
accessory nucleus of the upper spinal cord and terminating in the trapezius and
sternocleidomastoid muscles of the upper body.
COMPONENTS
The XIth nerve has only 1 component, i.e., motor axons that originate in the spinal
accessory nucleus in the upper spinal cord and innervate the trapezius and
sternocleidomastoid muscles of the upper body. Some authors classify the XIth nerve a
branchial (the chart on the next page does this), others call it somatic, and still others make a
good case that it is not a cranial nerve at all. In NBIO 401 we will remain agnostic on the
classification of the XIth nerve.
The chart and drawing on the next page summarize this information.
-Class 7 page 31-
NBIO 401
Fall 2013
Below we see the pathway from the motor cortex to the spinal accessory nucleus and then,
via the XIth nerve, to the trapezius and sternocleidomastoid muscles.
-Class 7 page 32-
NBIO 401
Fall 2013
CRANIAL NERVE XII - HYPOGLOSSAL
LOCATION
The hypoglossal (XIIth nerve) exits the medulla via the crease between the pyramid
(medially) and the inferior olive bulge (laterally). The caudal end of the hypoglossal nerve is
about even with the caudal end of the inferior olive bulge.
COMPONENTS
The XIIth nerve has only 1 component, somatic motor axons from motoneurons in the
hypoglossal nucleus to the tongue.
The chart and drawing on the next page summarize this information.
-Class 7 page 33-
NBIO 401
Fall 2013
Below we see the pathway from the motor cortex to the hypoglossal nucleus, which in turn
projects via the XIIth nerve to the tongue.
On the next 2 pages are summary diagrams showing the components of the cranial
nerves originating from motor nuclei or bringing information to sensory nuclei. The
information on these two summary diagrams is what you need to know for NBIO 401.
Specifically, I will not quiz you about the components of the cranial nerves that convey touch
and pain information from the skin of the ear to the spinal trigeminal nucleus.
-Class 7 page 34-
NBIO 401
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-Class 7 page 35-
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-Class 7 page 36-
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The final summary drawing is a famous illustration from Frank Netter showing sensory
(blue) and motor (red) components of each cranial nerve. This is a very good illustration but
it contains more information than you are responsible for in NBIO 401.
-Class 7 page 37-