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The Cranial Nerve Nuclei and the
Trigeminal System
General Organization of the Cranial Nerve
Nuclei and the Trigeminal System
I.
Introduction to the cranial nerves and nuclei
A. The 12 cranial nerves, their location, and
functions.
B. Categories of cranial nerves, and the
columnar organization of their nuclei.
II. Functional anatomy of the trigeminal system
A. Ascending pathway for touch (using main
trigeminal sensory nucleus).
B. Ascending pathway for pain and temp (using
spinal trigeminal nucleus).
General Organization of the Cranial Nerve
Nuclei and the Trigeminal System
III. Regional anatomy
A. Key components of the trigeminal system
within the medulla (e.g., spinal trigeminal
nucleus + tract).
B. Components within the pons – main
trigeminal
accessory nucleus.
C. Midbrain: mesencephalic trigeminal nucleus.
D. VPM + projections to 1° somatic sensory
cortex.
Fig. 6-1
I. Introduction to the Cranial Nerves
and Nuclei
A. 12 pairs:
I. Olfactory – enters telencephalon (cerebral
hemispheres).
II.Optic – a part of the diencephalon.
Both are purely sensory.
III. Oculomotor
IV. Trochlear – the only cranial nerve on
dorsal brainstem surface.
Both are purely motor and exit from midbrain.
I. Introduction to the Cranial Nerves
and Nuclei
12 pairs:
V. Trigeminal – in middle of pons – and have
mixed sensory/motor with separate roots.
VI. Abducens – motor
VII. Facial – mixed – muscles of facial
expression and taste.
VIII. Vestibulocochlear – sensory – vestibular
and auditory.
All originate at the ponto-medullary junction
I. Introduction to the Cranial Nerves
and Nuclei
12 pairs:
IX. Glossopharyngeal – mixed (main = sensory; post
1/3 of tongue for taste + pharynx).
X. Vagus – mixed – many functions: taste, visceral
sensory (i.e., gut, aortic arch receptors, peripheral
autonomic (gut, respiratory, cardiac), some
muscles (pharnyx, larynx, lungs).
XI. Spinal accessory – motor (neck muscles).
XII. Hypoglossal – motor (tongue muscles).
Mnemonics
• “On Old Olympus’ Towering Top, A Finn
And German Viewed A Hop”
Or more contemporarily:
• “Oh, Oh, Oh To Take A Family Vacation!
Go Vegas After Hours!”
To remember which are sensory and/or motor:
“Some Say Marry Money But My Brother
Says Better Brains Matter More”
Cranial nerves are analogous to spinal nerves
in many ways (as the bs is analogous to sc),
serving sensory and motor functions of the
head, rather than trunk and limbs.
1 Difference: a greater variety of sensory
modalities served - “special senses”, such
as sight and hearing.
B. Seven functional categories of cranial
nerves and the columnar organization of
their nuclei.
1. General somatic afferents [somatic sensations of head
(touch, pain, proprioception)].
2. General visceral afferents [visceral sensations,
chemoreception].
3. General somatic motor (inervation of striatal muscle].
4. General visceral motor [axons of autonomic neurons].
5. Spinal somatic afferents [vision, hearing, balance].
6. Spinal visceral afferents [taste, smell].
7. Special visceral motor [muscles from bronchial arches].
Cranial nerve nuclei:
Sensory, motor – analogous to dorsal,
ventral horn neurons of sc.
Organization of each category of nuclei in
rostral-caudal columns.
See Figs. 6-3 and 6-4
Columnar Organization of Cranial Nerve
Nuclei
Fig. 6-3
Note that sensory
columns are located
lateral to motor columns.
Cranial nuclei columns (Fig. 6-3)
Fig. 6-4
• General somatic motor  extraocular and tongue muscles.
• Spinal visceral motor  jaw, facial, throat, and many neck
muscles (derived from the broncial arch).
• General visceral motor  pre-ganglionic autonomics.
• Visceral afferents (general and spinal combined):
• Solitary Nucleus:
rostral  special – taste…VII, IX, X.
caudal  general – sometimes from visceral organs and
chemoreceptors…IX, X.
• Special somatic afferents - vestibular, cochlear
nuclei…VIII.
• General somatic afferents – trigeminal nuclei…V.
II. Functional Anatomy of the Trigeminal
System
• Serving somatic sensations of head.
• Analogous to dorsal column – medial lemniscal
and anterolateral systems of the lower body
(separate pathways mediate touch and pain-temp).
A.Ascending pathway for touch (using main
trigeminal sensory nucleus).
The most important cn in these systems is V (VII,
IX, X cover the small area shown in Fig. 6-6 –
Shows the ascending pathways.
Review for yourself that touch is mediated by largerdiameter myelinated axons.
Most neurons synapse in the main decussate in the
pons.
Trigeminal sensory nucleus  ascend in trigeminal
lemniscus (near medial lemniscus)  VPM (note
the other system used VPL)  1° sensory cortex
(specific area within the homonculus – lateral)
(Fig. 6-6A).
A smaller ipsilateral (non-decussating) pathway
processes mechanical stimuli from teeth and soft
tissues of the oral cavity.
B. Ascending pathway for pain/temp (using spinal
trigeminal nucleus).
* review diam, unmyelinated fibres enter at pons
and descend to the various levels (divisions) of the
spinal trigeminal nucleus.
Fig. 6-6A.
Ascending
Trigeminal
Pathways for
Touch:
main trigeminal
sensory nucleus
Fig. 6-6B. Trigeminal
pathway for Pain and
Temperature:
spinal trigeminal
nucleus
3 Components: oral,
interpolar, and caudal nuclei.
After synapsing, ascending
pathway is crossed and travels in
trigeminalthalamic tract of the
anterolateral system.
This path is important mainly for
facial and dental pain.
Pathway synapses onto VM 
past central gyrus for
discriminative aspect of pain and
also interlaminar nuclei  diffuse
projections for emotional aspects
of pain (should also be familiar).
III. Regional Anatomy of the Trigeminal
System
A. Cranial nerve involvement and key components within
medulla
3 trigeminal sensory roots, all serving different regions of
the head:
- opthalmic (skin, mucous membranes)
- maxillary (skin, mucous membranes)
- mandibular (includes most of mouth interior, except for
pharynx and post 1/3 of tongue). Fig. 6-8.
Note: very little overlap compared to spinal dermatomes 
significant regarding lesions.
Contributions from VII, IX, X: skin of ear (VII, X), larynx
(X), pharynx, post 1/3 of tongue (IX), dura mater (V, X).
Fig. 6-8.
Somatotopic
Organization:
Peripheral sensory ganglia:
V – semilunar
IX and X – superior
VII – geniculate
Specifically for stretch receptors of jaw muscles:
Soma contained in brainstem rather than in a
ganglion.
3rd trigeminal nucleus: mesencephalic trigeminal
nucleus.
Somatotropic organization of the ascending
trigeminal pathways: slices organized like an
‘inverted face’ (Fig. 6-8).
Rostral-caudal somatotropic organization of
medullary trigeminal spinal nuclei (like an onion
skin) (Fig. 6-8B).
May correspond to caudal, interpolar and oral
divisions.
Caudal Medullary Level (Fig. 6-9)
Spinal trigemenal nuc:
Organized much like sc
dorsal horn within the
caudal medulla
‘Rexed’s Laminae’
Spinal trigeminal tracts –
much like a continuation
of Lissauer’s Tract.
Reticular formation is
continuous with
intermediate zone.
Mid-medullary section
B. Components within the Pons – main trigemenal
sensory nucleus subserving touch (tactile
sensations of face, head, teeth).
This nucleus, along with the trigeminal lemniscus,
can be viewed in a pontine section: Fig. 6-12.
This is the trigeminal equivalent of dorsal column
nuclei.
Note: dorsal 1/3 of nucleus receives
mechanoreceptive signals from teeth and mouth
and gives rise to ipsilateral pathway (dorsal).
Therefore, VPM receives bilateral projections for
each region.
Pons (Fig. 6-12)
C. Midbrain: mesencephalic trigeminal nucleus.
As noted earlier, this nucleus is equivalent to a ganglion,
containing the axons of jaw, muscle stretch receptors.
Found in midbrain, in lateral portions of periaquaductal grey
(PAG).
A projection to trig motor n. mediates the jaw jerk reflex
(analogous to knee-jerk reflex).
In this section, can also see trig lemniscus (med to med lem).
D. Thalamus (VPM) and projections to 1° somatic sensory cortex.
Fig. 6-14: VPL: somatic sensations from trunk and limbs.
VPM: somatic sensations from head (medial magnocellular).
VPM: somatic sensations from taste relay nuc. (parvocellular) 
Projections to 1° somatic sensory cortex (face area, Fig. 6-15).
Fig. 6-14
Fig. 6-15:
“Face Area” of
Primary Somatic
Sensory Cortex: