Cranial nerve nuclei
Oculomotor nerve (III)
- somatic motor (GSE) in rostral midbrain; extrinsic eye muscles
- autonomic visceral motor (GVE) – sphincter pupillae and ciliary muscles; preganglionic parasympathetic
Trochlear nerve (IV)
- somatic motor (GSE) – in caudal midbrain; superior oblique muscles
Abducens nerve (VI)
- somatic motor (GSE) – caudal pons; lateral rectus muscle
Hypoglossal muscle (XII)
-somatic motor (GSE) - intrinsic/extrinsic muscles of tongue
1. Trigeminal nerve (V)
- branchial motor root (SVE) for mastication and tensor tympani is at midpontine level in between midline and sulcus limitans (SL)
- sensory parts of trigeminal feed into reflexes, pathways to cerebellum, and pathways to thalamus (touch/position and pain/temp). Somatic sensory nuclei are lateral to SL
- main sensory nucleus of trigeminal (midpontine level) located where trigeminal nerve enters brainstem;
- the main sensory nucleus merges with inferiorly with spinal nucleus (from midpontine level to upper cervical spinal cord); it merges with the dorsal horn
- The most superior mesencephalic nucleus extends from rostral midbrain to midpontine level; pseudounipolar afferent collection; should be in periphery, but is in CNS; The cell bodies of master muscle spindle afferents (and other mechanoreceptors) in the mouth around temporomandibular joint comprise mesencephalic nucleus; mesencephalic tract is made up of processes of these primary afferents (act as central branches of trigeminal ganglion cells)
Pain/Temp (contralateral representation in cortex)
1. Small-diameter trigeminal primary afferents (with cell bodies in trigeminal ganglion) turn caudally after entering pons traveling laterally to the spinal trigeminal nucleus in spinal trigeminal tract
2. At caudal medulla they begin to terminate in spinal trigeminal nucleus, which contains second-order neurons that cross midline, join the STT, and project to thalamus
- pain/temp mapping in spinal trigeminal nucleus; rostral-caudal order in which pain/temp fibers terminate in the spinal trigeminal nucleus: parts of face nearest cervical dermatomes (laterally) are represented in most caudal part of medulla; parts of face nearest mouth and nose (midline) are represented nearer the level of the obex (rostrally);
- ipsilateral half of face represented upside down: neurons in ventral parts of spinal nucleus respond to areas of face in ophthalmic distribution and neurons in mandibular division are most dorsal; this arrangement allows for smooth transition from spinal levels processing cutaneous info from back of head to brainstem levels processing similar cutaneous info from face

Touch/position (contralateral representation in cortex) –
1. Large-diameter trigeminal primary afferents end directly in main sensory nucleus
2. Axons of second-order neurons cross midline, join medial lemniscus, and project to thalamus
Jaw-Jerk Reflex-
1. Masseter stretch receptors have cell bodies in mesencephalic nucleus
2. Their central processes synapse on masseter motor neurons (in motor nuclei)
Blink reflex (withdrawal reflex) – touch one cornea and both eyes blink
1. interneurons in trigeminal spinal nucleus which project bilaterally to facial motor nucleus
2. Afferents carrying light touch information end at these levels of the spinal nucleus
3. Second order neurons cross the midline to join STT and project to thalamus
3. Facial Nerve (VII)
- branchial motor nucleus (SVE) in caudal pons near STT between midline and sulcus limitans
(SL) – facial muscles, stylohyoid, ant posterior digastric
- visceral motor (GVE) in caudal pons immediately medial to SL – nasal, lacrimal, palatine glands, sublingual/submandibular glands
- special sensory/ visceral sensory at pontomedullary junction immediately lateral to SL – taste in palate and ant 2/3 of tongue
- afferents travel through solitary tract until they reach the appropriate level of the surrounding nucleus of the solitary tract, where they synapse
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second order neurons in solitary tract nucleus project to visceral reflex arcs, taste cortex via thalamus, to hypothalamus (uncrossed). Taste afferents end in most rostral part of solitary tract nucleus
- efferents are LMN for muscle of facial expression and stapedius; axons of motor neurons wrap around abducens nucleus forming internal genu of the facial nerve before leaving brainstem; paralysis in ipsilateral face and lowered threshold in ipsilateral ear
Glossopharyngeal nerve (IX)
- special/ general visceral/somatic afferents – in nucleus of solitary tract in rostral medulla – SA: taste post 1/3 tongue, Somatic: post 1/3 tongue, pharynx, middle ear, carotid body and sinus
- branchial motor neurons (SVE) in rostral medulla between midline and SL – stylopharyngeus muscle
- visceral motor neuron (GVE) – rostral medulla; parotid gland
- Taste (post 1/3 tongue) afferents enter solitary tract and end in surrounding nucleus caudal to where facial taste afferents end. ; somatic afferents enter solitary tract nucleus more caudally
(CV and resp. reflexes)
-LMNs of larynx/pharynx muscles located in brainstem tegmentum near STT; not concentrated in visible nucleus; they, instead, form a diffuse column called nucleus ambiguus (extends longitudinally through rostral medulla); Most rostral through IX to ipsilateral stylopharyngeus

Vagus nerve (X)
- Visceral sensory afferents – in nucleus of solitary tract at caudal medulla; viscera supplied by
GVE fibers; enter solitary tract and end in caudal parts of nucleus of solitary tract feeding into visceral reflexes
- Special afferents (visceral sensory) in nucleus of solitary tract at caudal medulla; taste, epiglottis
- branchial motor neurons (SVE) in caudal medulla between midline and SL in nucleus ambiguus
– skeletal muscle of palate/pharynx/larynx/esophagus;
- visceral motor neurons (GVE) – caudal medulla; thoracic and abdominal viscera to left of colic flexure; preganglionic parasympathetic neurons live in dorsal motor nucleus of vagus and project through vagus to viscera
Accessory Nerve (XI) –
- branchial motor neurons (SVE) – ipsilateral trapezius, SCM, nucleus is in cervical cord (ventral horn) and caudal medulla
Corticobulbar tract –
UMN of brainstem; start from motor cortex and descend through internal capsule and cerebral peduncle, they cross the midline when they get near the level of the nucleus they will innervate
-many cranial nerve nuclei receive corticobulbar innervation from both cerebral hemispheres
- variation exists in crossed:uncrossed projections from one hemisphere
- muscles contracted bilaterally and symmetrically (forehead, pharynx/larynx) have bilateral corticobulbar inputs
- independently contracted muscles (orbicularis oris) get crossed inputs
- UMN damage on one side causes weakness of contralateral lower quadrant of face, weakness of contralateral masseter/trapezius, contralateral weakness of tongue, no problems with larynx/pharynx, ipsilateral SCM weakness