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Embryonic cranial nerve nuclei are organized segmentally. A. In the developing hindbrain (seen here from the ventral side) special and general visceral
motor neurons form in each hindbrain segment (rhombomere) except rhombomere 1 (r1). Each special visceral motor nucleus comprises neurons in two
rhombomeres: the trigeminal nucleus is formed by neurons in r2 and r3, the facial nucleus by neurons in r4 and r5, the glossopharyngeal nucleus by
neurons in r6 and r7, and the motor nuclei of the vagus by neurons in r7 and r8. Axons of neurons in each of these nuclei course laterally within the brain,
leaving the brain through exit points in the lateral neuroepithelium (of r2, r4, r6, and r7) and running together outside the brain to form the respective cranial
motor nerves (V, VII, IX, X). The trigeminal (V) nerve innervates muscles in the 1st branchial arch, the facial (VII) nerve innervates muscles in the 2nd
Source: The Sensory, Motor, and Reflex Functions of the Brain Stem, Principles of Neural Science, Fifth Editon
branchial arch, and the glossopharyngeal (IX) nerve innervates muscles in the 3rd branchial arch.
Citation: Kandel ER, Schwartz JH, Jessell TM, Siegelbaum SA, Hudspeth AJ, Mack S. Principles of Neural Science, Fifth Editon; 2012 Available
All of the visceral motor neurons (green) develop initially next to the floor plate at the ventral midline; after extending their axons toward their respective
at: http://mhmedical.com/ Accessed: April 28, 2017
exit points, the cell bodies then migrate laterally (arrows). Exceptions are the facial motor neurons formed in r4 (red); the cell bodies, after extending their
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axons toward the exit point, migrate caudally to the axial level of r6 before migrating laterally.