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 efferentparasympathetic 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
This diagram concisely shows where each nucleus lies. Note that sensory nuclei are shown on the left of the picture, motor nuclei on the right.
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

 

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