Neurosurgery notes/Anatomy/Embryology/Parasympathetic development

Parasympathetic development

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Embryology
  • Parasympathetic ganglia
    • form in the 4th week close to the organs they are destined to innervate.
      • In contrast to sympathetic ganglia, which form relatively far from the organs they are destined to innervate.
    • Preganglionic parasympathetic neurons
      • Reside in
        • One of four motor nuclei in the brainstem (III, VII, IX, and X) or
        • Intermediolateral cell columns of the sacral cord (S2-S4).
      • Innervation
        • Cranial nuclei supply the head and the viscera superior to the hindgut,
        • Sacral neurons supply the viscera inferior to this point.
      • The preganglionic parasympathetic fibers associated with cranial nerves III, VII, and IX travel to parasympathetic ganglia located near the structures to be innervated, where they synapse with the second (postganglionic or postsynaptic) neuron of the pathway.
        • Organs receiving parasympathetic innervation in this way include
          • Dilator pupillae muscles of the eye,
          • Lacrimal and salivary glands,
          • Glands of the oral and nasal mucosa.
        • The neurons and glia in each ganglion arise from neural crest cells located at roughly the same level as the corresponding brain stem nucleus.
          • Ciliary ganglion of the oculomotor nerve (III) is formed by neural crest cells arising in the caudal part of the diencephalon and the cranial part of the mesencephalon.
          • Sphenopalatine and submandibular ganglia of the facial nerve (VII) are formed by neural crest cells that migrate from the cranial rhombencephalon.
          • Otic ganglion of the glossopharyngeal nerve (IX) and the enteric ganglia served by the vagus nerve are derived from neural crest cells originating in the caudal portion of the rhombencephalon.
          • In contrast, the preganglionic parasympathetic fibers associated with cranial nerve X join with somatic motor and sensory fibers to form the vagus nerve.
            • Some branches of the vagus nerve serve structures in the head and neck, but other parasympathetic and sensory fibers within the nerve continue into the thorax and abdomen, where the parasympathetic fibers synapse with postganglionic neurons in numerous small parasympathetic ganglia embedded in the walls of target organs such as heart, liver, suprarenal cortex, kidney, gonads, and gut.