1.
Trigeminal nerve
(thin myelinated/ unmyelinated fibers; midpons)
Neuro Objectives 23
Trigeminal nerve contents : general sensory afferents of the face and anterior
2/3 of the tongue; special visceral efferents to the muscles of mastication
Trigeminal nuclei location : a.
Spinal nucleus : mediolateral in the medulla and caudal pons b.
Main sensory nucleus : dorsolateral in the midpons; dorsal to motor nucleus c.
Motor nucleus : dorsolateral in the midpons; ventral to main sensory nucleus d.
Mesencephalic nucleus : mediolateral in the rostral pons and medulla; actually NOT a nucleus, but a ganglia for psuedounipolar primary afferents (mostly mechanoreceptors from muscles around temporomandibular junction)
Central pathways : a.
Pain/temperature : midline
Thalamus
Spinal trigeminal tract
Spinal nucleus
(caudal medulla)
Spinothalamic tract

b.
Touch/position : midline
Thalamus
Trigeminal nerve
(thick myelinated fibers; midpons)
2.
Main sensory nucleus
Medial lemniscus
Somatotopic arrangement of fibers/terminations in the spinal tract/nucleus :
The more anterior (CN V
1
) sensory aspects terminate anteriorly in the spinal nucleus (near the obex) while the posterior (CN V
3
) sensory aspects terminate posteriorly in the spinal nucleus (in the caudal medulla)
3. Facial motor nucleus location : medial to the spinothalamic tract in the caudal pons
Pathway of facial nerve fibers : leave the facial motor nuclei dorsally and wrap around the adbucens nucleus (internal genu of the facial nerve) before leaving the caudal pons
4.
5.
6.
Motor neurons for the pharynx/larynx (IX, X) : Nucleus ambiguus (blends into reticular formation ventrolaterally in the medulla)
Pre-ganglionic parasympathetic neuron location (CN X) : Dorsal motor nucleus of vagus (between hypoglossal nucleus and sulcus limitans in the caudal medulla)
Visceral afferent pathway (CN VII, IX, X) : Solitary nucleus (ventral to the floor of the 4 th
ventricle and lateral to sulcus limitans in the medulla and caudal pons)
7. Gustatory information pathway (CN VII, IX) : Rostrolateral part of solitary nucleus (ventral to the 4 th
ventricle and lateral to sulcus limitans in the rostral medulla and caudal pons)

8. Neural circuitry of : a.
Jaw-jerk reflex (CN V) : mesencephalic nucleus
Muscle spindle
Masseter
Motor ending trigeminal motor root b.
Blink reflex (CN V afferent, CN VII efferent) :
Eye touch
Orbicularis
oculi
V sensory afferent
VII facial
motor
nuclei mesencephalic tract trigeminal motor nucleus
V spinal nucleus

9. Effects of damage : a.
Trigeminal motor nucleus : a.
Nucleus damage : ipsilateral weakness in the muscles of mastication b.
Corticobulbar damage : slight contralateral weakness in the muscles of mastication b.
Facial motor nucleus : a.
Nucleus damage : ipsilateral weakness in all the facial muscles b.
Corticobulbar damage : contralateral weakness in the lower face muscles (bilateral projection to upper face) c.
Nucleus ambiguus : a.
Nucleus damage : ipsilateral weakness in the larynx/pharynx b.
Corticobulbar damage : no real effect (bilateral projection to the larynx/pharynx) d.
Accessory nucleus : a.
Nucleus damage : ipsilateral weakness in the sternocleidomastoid b.
Corticobulbar damage : ipsilateral weakness in the sternocleidomastoid (contralateral head rotation) e.
Hypoglossal nucleus : a.
Nucleus damage : ipsilateral weakness in the tongue b.
Corticobulbar damage : slight contralateral weakness in contralateral tongue
10. Location/contents of : a.
Spinal trigeminal tract/nucleus : a.
Location : mediolateral extending from the caudal medulla to the caudal pons b.
Contents : primary facial pain/temperature afferents (CN V) b.
Main sensory nucleus of trigeminal : a.
Location : dorsolateral to the area where trigeminal fibers enter the midpons (mediolateral caudal pons, dorsolateral to motor nucleus of c.
trigeminal) b.
Contents : primary facial touch/position afferents (CN V)
Motor nucleus of trigeminal : a.
Location : where trigeminal fibers enter the midpons (mediolateral caudal pons, ventromedial to main sensory nucleus of trigeminal) b.
Contents : Primary efferents to the muscles of mastication (CN V) d.
Motor nucleus of facial : e.
a.
Location : medial to spinothalamic tract in the caudal pons b.
Contents : ipsilateral lower motor neurons (CN VII)
Internal genu of facial : a.
Location : facial wraps ventromedially around the abducens nucleus near the midline and 4 th ventricle in the caudal pons b.
Contents : lower motor neuron axons leaving the motor nucleus of the facial nerve (CN VII)

f.
Solitary tract/nucleus : a.
Location : ventral to the floor of the 4 th ventricle and lateral to sulcus limitans in the medulla b.
Contents : site of primary visceral afferent termination of the tongue
(CN VII, IX) and abdomen (CN X) g.
Nucleus ambiguus : a.
Location : blends into the posterolateral reticular formation in the medulla b.
Contents : branchial muscle efferents to larynx/pharynx (CN IX, X) h.
Dorsal motor nucleus of vagus : a.
Location : lateral to hypoglossal nucleus and medial to sulcus limitans in the rostral medulla b.
Contents : preganglionic parasympathetic efferents to the abdomen
(CN X)