Cranial Nerve Nuclei

Summary

• The cranial nerve nuclei
  • Key rules of brainstem nuclei

The Cranial Nerve Nuclei

• Cranial nerves are numbered from how their nuclei are ordered, rostral to caudal (i.e. front to back/superior to inferior).
  • The names reflect general distribution/function.

• There are 12 nuclei for the 12 cranial nerves (remember in groups of 4)
  1. Four above pons
     • CNI and CNII are not in the brainstem and lie in the cerebrum
       • CNI to the forebrain
       • CNII to the thalamus + occipital lobe
     • CNIII and CNIV nuclei are in the midbrain
  2. Four in pons
     • CNV nuclei span the brainstem
     • CNVIII at pontomedullary junction
     • CNVI and CNVII lie in-between
  3. 4 in medulla

• Note that there are 4 types of cranial nerve nuclei:
  1. Afferents (sensory are towards the side)
     • These contain cell bodies of primary neurones (analogous to the DRG in spinal nerves)
  2. Somatic efferent (motor are medial)
     • Within the brainstem
     • Contain cell bodes of motor cranial nerves
     • Analogous to the ventral horn in spinal nerves
  3. Visceral efferent – parasympathetic fibres that correspond to a somatic efferent of the same nerve.
     • Note that there is 1 nucleus per region of the brainstem
       1. Edinger-Westphal for CNIII (in midbrain)
       2. Superior salivary for CNVII (in pons)
       3. Inferior salivary for CNIX (at pontine-medullary junction)
       4. Dorsal Nucleus of Vagus Nerve for CNX (medulla)
     • 1 combined nucleus – Nucleus Ambiguus
       • Combines for CNIX, CNX, and XI
  4. Parasympathetic sensory comes from one nucleus
     • Nucleus Solitarius – sensory (SVA, GVA) for several nerves
       • Contains CNVII, CNIX, CNX

Key Rules of brainstem nuclei

1. Brainstem nuclei lie where cranial nerve exits the brainstem
   • 2 of each nuclei (one for each side)
2. Motor and sensory fibres will have independent nuclei for the same cranial nerve
   • Motor nuclei in the Middle
   • Sensory nuclei on the Side
   • Parasympathetic nuclei – one in each section + combined nuclei
3. CNV is special
   • Combines parasympathetic and sensory neurones
   • Sensory nucleus spans across brainstem
   • Carries visceral afferents from other nerves (trigeminothalamic tract)
4. NB some sensory nuclei are unusual
   • CNV sensory nucleus combines parasympathetic/sensory nuclei
   • Vestibulocochlear nucleus is in 2 parts (CNVIII is 2 nerves)
   • CNXI nucleus lies primarily in SC
     • Collaterals from nucleus ambiguus in medulla
5. Nucleus ambiguus and solitarius are the only combined nucleus’ – both are:
   1. In the medulla
   2. Parasympathetic + to visceral structures