CN 5: Nuclei

CN 5: Nuclei

First, we will draw the anatomy of the trigeminal ganglion.
Draw the trifurcated trigeminal ganglion of the trigeminal nerve.
Its name means the “three twins.”
Indicate that it lies in a low depression known as the trigeminal impression at the apex of the petrous temporal bone.
Next, begin a table.
Write Trigeminal Ganglion and underneath, write: Divisions, Foramen, and Function.
Now show that from rostral to caudal, the divisions of the trigeminal ganglion are:

1. The ophthalmic division, which traverses the superior orbital fissure.
2. The maxillary division, which traverses foramen rotundum.
3. The mandibular division, which traverses foramen ovale.
   Indicate that sensory input ascends through all three divisions but that motor output descends through the mandibular division, only.
   The motor division of the trigeminal nerve passes ventrolaterally through the cerebellopontine angle cistern to exit the brainstem and joins the mandibular division as it exits the middle cranial fossa through foramen ovale to innervate the muscles of mastication.
   Lastly, indicate that the trigeminal ganglion is enveloped in Meckel’s cave — a dural-based, cerebrospinal fluid-filled cavern that lies adjacent to the posterolateral aspect of the cavernous sinus.
   Next, we will draw the anatomy of the trigeminal nuclei.
   Include the headers: Nucleus and Function
   In our table, include:
   1 motor nucleus: the trigeminal motor nucleus, and
   3 sensory nuclei: the principal sensory nucleus, mesencephalic nucleus, and spinal trigeminal nucleus.
   Now, let’s draw these nuclei.  Draw a sagittal view of the brainstem: label the midbrain, pons, and medulla; include the upper cervical cord and draw the superior colliculus in the midbrain.
   First, in the upper pons, draw the trigeminal motor and principal sensory nuclei.
   Next, draw an axial section through the upper pons.  Include the posterior/anterior axis.
   We will use this section to differentiate the trigeminal motor and principal sensory nuclei.
   Show that the trigeminal motor nucleus lies medial to the principal sensory nucleus in the dorsal pons.
   Both lie just above the abducens nucleus.
   Whereas the principal sensory and motor trigeminal nuclei are restricted to this upper pontine level, the two other trigeminal sensory nuclei combined span the height of the brainstem and upper cervical spinal cord.
   Next, show that the mesencephalic nucleus spans from the upper pons to the superior colliculus.
   The mesencephalic nucleus contains the primary sensory neurons for proprioceptive afferents from the muscles of mastication, which ascend through the mandibular division of the trigeminal nerve.
   Indicate that the mesencephalic nucleus is the only central nervous system nucleus to house primary sensory neurons: the primary sensory neurons of the mesencephalic sensory afferents do not lie within a peripheral ganglion.
   Notably, the mesencephalic nucleus projects to the trigeminal motor nucleus to produce the masseter reflex (the jaw jerk).
   Now, show that the spinal trigeminal nucleus and tract span from the upper pons to the upper cervical spinal cord (anywhere from C2 to C4).
   Trigeminal sensory afferents descend the spinal trigeminal tract and then synapse in the adjacent spinal trigeminal nucleus in a specific somatotopic pattern, drawn elsewhere. The caudal end of the spinal trigeminal nucleus is continuous with the substantia gelatinosa, which lies within the dorsal horn of the spinal cord, and the spinal trigeminal tract is continuous with the posterolateral fasciculus (aka Lissauer's tract), which lies along the dorsal edge of the dorsal horn of the spinal cord.