212 Neuroanatomy: Draw It to Know It
Know-It Points
Cranial Nerve 5: Peripheral Innervation
■ Th e peripheral divisions of the trigeminal nerve are
division 1 — the ophthalmic division, which covers
the eyes; division 2 — the maxillary division, which
covers the cheeks; and division 3 — the mandibular
division, which covers the jaw.
■ Th e main function of the trigeminal motor system is
mastication (ie, chewing ), which requires the
trigeminally innervated medial and lateral pterygoids,
masseter, and temporalis muscles.
■ In a lower trigeminal motor neuron lesion (eg, when
a trigeminal motor nucleus or nerve is injured or
when a lateral pterygoid is damaged), the jaw deviates
toward the injured side.Cranial Nerve 5: Nuclei
■ Th e trigeminal ganglion lies in Meckel’s cave: a
dural-based, cerebrospinal fl uid-fi lled cavern that lies
along the posterolateral aspect of the cavernous sinus.
■ Th e ophthalmic division traverses the superior orbital
fi ssure; the maxillary division traverses foramen
rotundum; and the mandibular division traverses
foramen ovale.
■ Th e ophthalmic and maxillary divisions (divisions 1
and 2, respectively) pass through the lateral wall of
the cavernous sinus and then merge together along
with the mandibular division to form the trigeminal
ganglion within Meckel’s cave.
■ Th e trigeminal motor nucleus and the principal
sensory nucleus lie in parallel just above the abducens
nucleus in the upper pons.
■ Th e mesencephalic nucleus spans from the upper
pons to the level of the superior colliculus (in the
midbrain).
■ Th e spinal trigeminal nucleus and tract span from
the upper pons to the upper cervical spinal cord.
■ Th e motor division of the trigeminal nerve passes
through the cerebellopontine angle cistern and joins
the mandibular division as it exits the middle cranial
fossa through foramen ovale.Cranial Nerve 5: Tracts ( Advanced )
■ Th e central sensory aff erents of the trigeminal nerve
relay to the cortex through two diff erent
trigeminothalamic pathways: anterior and posterior.
■ S m a l l fi ber sensory modality trigeminal nerve fi bers
project to the spinal trigeminal tract and nucleus and
large fi ber sensory modality trigeminal nerve fi bers
project to the principal sensory nucleus.
■ Th e spinal trigeminal nucleus divides from superior
to inferior into pars oralis, pars interpolaris, and pars
c a u d a l i s.Cranial Nerve 7: Innervation
■ Th e upper division of the facial nucleus receives
bilateral corticonuclear projections and the lower
division receives contralateral projections, only.
■ Fibers from the upper division innervate the upper
face and fi bers from the lower division innervate
the lower face.
■ In a right cerebral cortical stroke, the left upper face is
strong and the left lower face is weak.
■ In a left Bell’s palsy, both the left upper face and left
lower face are weak.