Trigeminal nerve (ch 12) Flashcards
what other CNs use CN V as a street to get where they are going?
CN VII: lacrimal gland; anterior 2/3 of the tongue
CN IX: submandibular gland
what is the largest CN?
Trigeminal
CN V is a ___ nerve?
mixed
large motor component
even larger sensory component
what is the functional component of CN V?
GSA
SVE
the motor root supplies:
the muscles of mastication:
temporalis
masseter
medial & lateral pterygoids
also smaller muscles: tensor tympani tensor veli palatini mylohyoid anterior belly of digastric
*these muscles arise embryologically from the first branchial arch– SVE
the sensory root supplies:
face mouth nasal cavity orbit anterior half of the scalp dura mater
what are the 3 portions of the trigeminal nerve? and what do their sensory branches innervate?
V1- opthalmic
-skin of the forehead and nose
(no proprioceptors or motor fibers)
V2- maxillary
-cheeks and upper lip
(discriminative fibers to cheek, no motor or prop)
V3- mandibular
-lateral side of the face and lower jaw
(motor (SVE, ipsilateral) and proprioceptors, pain receptors, discriminative sensations)
what are the 4 nuclei of the trigeminal nerve?
(nuclei range from midbrain to ~C3)
spinal- lower pons, medulla and upper SC
main sensory nucleus- middle pons
motor nucleus- middle pons
mesencephalic- upper pons and midbrain
where is the mesencephalic nucleus and what does it control?
most rostral nucleus
located in the dorsolateral part of the pontine tegmentum and the lateral periaquductal gray area of the midbrain
GSA
unipolar cells
conveys stretch information to neurons in the motor nucleus of V (group Ia, Ib, II from ms spindles/proprioceptors of the mandible)
stretch reflex
trigeminal afferents from mechanioreceptors for tactile discrimination, joint position sense, and pressure sensation terminate in the :
principle/main sensory nucleus of nerve V
analogous to dorsal column nuclei- discriminative sensations (2pt, vibration, texture, touch) (group II fibers)
GSA- discriminative sensations to face (touch and pressure)
fibers of trigeminal ganglion cells mediating the sensations of pain, temperature and light touch form the:
spinal tract of the trigeminal nerve– gives off terminal branches to the nucleus of the spinal tract of V
where is the motor nucleus of V located and what does it do?
fibers from the motor nucleus of V in the lateral tegmentum of the rostral pons enter the mandibular branch of the trigeminal nerve and innervate the muscles of mastication
SVE
jaw jerk
why does the mandibular division have proprioceptors? where do the fibers go?
because the jaw moves
goes into mandibular division of trigeminal and goes to the mesencephalic nucleus (receiving end for large afferents group I, II)
motor fibers (SVE) go to motor nucleus
what are the 3 parts of the spinal nucleus?
1- caudalis analogous with nucleus proprius -wide dynamic range neurons -concerned with pain & temp to the FACE -somatotopically arranged (V1-ventrolat; V3-dorsomed)
2- interpolaris
sensation to the TEETH
3- oralis
- similar to main
- touch from MOUTH, LIPS and nose
what is jaw jerk?
a stretch reflex obtained by placing the examiner’s index finger over the middle of the patient’s chin with the patient’s mouth slightly open and tapping the finger gently with a reflex hammer
normal response= slight contraction of the masseter and temporal is muscles bilaterally, causing the jaw to close slightly
exaggerated by UMN lesions rostral to the level of the pons
decreased/absent with lesions that interrupt the reflex arc
what is the VTTT? how is it formed?
ventral trigeminothalamic tract
formed by the fibers arising from cells of the nucleus of the spinal tract that cross to the opposite side of the brain stem to form the VTTT
they then ascend with the spinothalamic tract through the pons and midbrain to the medial part of the VPM of the thalamus
what is the VPM?
ventral posteromedial nucleus of the thalamus
what does the VTTT process?
inputs from pain, thermal and touch receptors in the skin throughout the distribution of the trigeminal nerve and from small area of skin in the auricle (innervated by GSAs in CN VII, IX and X)
branches of the 5th CN mediate pain sensation from the cornea, the mucous membranes of the oral and nasal cavities, the teeth, and the dura in the anterior part of the cranial cavity
what is the DTTT? how is it formed?
dorsal trigeminothalamic tract
trigeminal nerve fibers from mechanoreceptors for tactile discrimination project to the principle sensory nucleus and to the rostral part of the nucleus of the spinal tract (these neurons function similarly to those of the NG and NC- send crossed fibers to accompany the contralateral medial lemniscus).
these crossed fibers terminate in the VPM, but they project to neurons separate from those receiving projections from the intermediate and caudal parts of the spinal nucleus of V. In addition, the dorsal portion of the principal sensory nucleus gives off a fascicle of uncrossed fibers that ascend to the ipsilateral VPM as part of the central segmental tract- these fibers are termed the DTTT
what are the pain and temp afferents of the head?
CN V- face
CN VII- skin external ear, ext auditory meatus
CN IX: ear, post 1/3 tongue, auditory
CN X: ear, lower pharynx, upper esophagus
**all do pain and temp but all terminate on spinal nucleus of V !!!!
synapse on 2nd order neurons, cross over and ascend to thalamus to form VTTT
what is the corneal blink reflex?
when a foreign body touches the cornea of one eye, the reflex evokes prompt closure of BOTH eyelids.
sensory fibers entering the upper part of the spinal tract of V synapse with cells of the nucleus of the spinal tract, which sends axons to the nucleus of the facial nerve. –> motor fibers of the facial nerve then activate the orbicular is oculi muscle to close the eye on the side that had been touched. interneurons in the nucleus of the spinal tract project to the facial nucleus of the opposite side, where they synapse on motoneurons that close the eye on that side too
the response on the side stimulated is termed:
direct corneal reflex
the response in the contralateral eye is termed:
consenual corneal reflex
interruptions of the trigeminal nerve on one side:
abolishes BOTH the direct and the consensual response to stimulation
a disorder affecting the facial nerve on one side:
touching the ipsilateral cornea does not evoke a direct response but does evoke a consensual response and also increases lacrimation
lesions in the lateral part of the medulla or lower pons that damage the spinal tract of V frequently include:
the spinothalamic tract as well causing loss of pain and temp sense on the SAME side of the face as the lesion and loss of pain and temp sense on the OPPOSITE side of the body beginning at the neck
what is trigeminal neuralgia? what are trigger zones?
“tic douloureux”
episodic paroxysmal pain
disorder characterized by attacks of unbearably severe pain lasting only for seconds over the distribution of 1 or more branches of the trigeminal nerve
may have TRIGGER ZONES- stimulation by light touch, temp changes, or facial movement that may set off pain
unknown cause- may be compression of the trigeminal nerve by a small artery
(viral, autoimmune, lyme or idiopathic)??
