During embryonic development, there is a vertical column in the brain stem from which the different nerve fiber types are derived. As the fetus develops, the column splits into different columns, which migrate away from it. In the mature nervous system, afferent cranial nuclei tend to lie more laterally in the brain stem, while efferent nuclei lie medially.
The most medially placed of the somatic efferent nuclei are termed general somatic efferent nuclei, and lie caudally to rostrally in the order oculomotor (III), abducens (VI), hypoglossal (XII), and accessory (XI). These nuclei innervate muscles that are derived from the embryonic somites; these muscles are termed myotome muscles. The oculomotor nucleus lies in the ventral apex of the peri-aqueductal gray matter at superior collicu-lar level. Its efferent nerve fibers constitute the oculomotor nerve, and innervate the extraocular muscles with the exception of the superior oblique, and the leva-tor palpebrae superioris. The trochlear nucleus lies at the level of the inferior col-liculus, and its efferents supply the superior oblique muscle of the eye. The hypo-glossal efferents innervate the extrinsic and intrinsic muscles of the tongue.
The somatic efferent nuclei that have migrated more laterally from the midline of the brain stem are the motor trigemi-nal nucleus (V), facial nucleus (VII), and the nucleus ambiguus (IX). They are termed special somatic efferent nuclei. They innervate muscles derived from the branchial arches. These are striated muscles of the pharynx, and the masticatory and facial muscles.
Lateral to the special somatic efferent nuclei are the parasympathetic visceral efferent nuclei. These are the Edinger-Westphal oculomotor nucleus (III), the superior (VII) and inferior (IX) salivatory nuclei, and the dorsal motor nucleus of the vagus (X). The visceral afferents terminate in one nucleus, the nucleus of the tractus solitarius. The Edinger-Westphal nucleus is the most rostrally placed, and lies in the periaqueductal gray matter near the oculomotor nucleus. Its efferents terminate in the ciliary ganglion, from where postganglionic efferents travel to the ciliary muscles and sphincter pupillae of the eye. The dorsal motor nucleus of the vagus is the largest of the parasympathetic pre-ganglionic nuclei, and lies beneath the floor of the fourth ventricle. Its efferents travel to many different visceral abdominal and thoracic targets. The superior and inferior salivatory nuclei lie in the tegmen-tum of the pons. The superior salivatory nucleus projects efferents in the facial nerve, and these supply the pterygo-palatine and submandibular ganglia. The postganglionic efferents travel to the mucous membranes of the mouth and nose and the lacrimal glands, and the sub-mandibular efferents to the sublingual and submandibular glands.
The somatic afferent nuclei are the most laterally placed of the cranial nerve nuclei. These are the trigeminal nucleus (V), the cochlear nuclei (VIII), and the vestibular nuclei(VIII). The term special sensory has been used to describe the olfactory and optic nerves, because of their origins in the specialized sensory organs, namely the nasal epithelium and the eye, respectively, and because of their fore-brain origins, as opposed to the brain stem origins of the other cranial nerve nuclei.
oculomotor, nucleus trochlear, nucleus trigeminal, motor nucleus abducens. nucleus facial motor, nucleus superior.
oculomotor, nucleus trochlear, nucleus trigeminal, motor nucleus
positions of efferent cranial nuclei on left, and afferent nuclei on right fdinger-Westphal nucleus trigeminal sensory nucleus salivatory nuclei dorsal motor, nucleus of the vagus nucleus, ambiguus hypoglossal nucleus accessory, nucleus positions of efferent cranial nuclei on left, and afferent nuclei on right nucleus solitarius
medial vestibular (VIM)
position of columns of the cranial nuclei; level of medulla somatic afferent visceral, afferent visceral, efferent somatii efferent position of columns of the cranial nuclei; level of medulla medial vestibular (VIM)
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