Trigeminal nerve (ch 12)

Question 1

what other CNs use CN V as a street to get where they are going?

Answer 1

CN VII: lacrimal gland; anterior 2/3 of the tongue

CN IX: submandibular gland

Question 2

what is the largest CN?

Answer 2

Trigeminal

Question 3

CN V is a ___ nerve?

Answer 3

mixed

large motor component
even larger sensory component

Question 4

what is the functional component of CN V?

Answer 4

GSA

SVE

Question 5

the motor root supplies:

Answer 5

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

Question 6

the sensory root supplies:

Answer 6

face
mouth
nasal cavity
orbit
anterior half of the scalp
dura mater

Question 7

what are the 3 portions of the trigeminal nerve? and what do their sensory branches innervate?

Answer 7

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)

Question 8

what are the 4 nuclei of the trigeminal nerve?

Answer 8

(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

Question 9

where is the mesencephalic nucleus and what does it control?

Answer 9

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

Question 10

trigeminal afferents from mechanioreceptors for tactile discrimination, joint position sense, and pressure sensation terminate in the :

Answer 10

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)

Question 11

fibers of trigeminal ganglion cells mediating the sensations of pain, temperature and light touch form the:

Answer 11

spinal tract of the trigeminal nerve– gives off terminal branches to the nucleus of the spinal tract of V

Question 12

where is the motor nucleus of V located and what does it do?

Answer 12

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

Question 13

why does the mandibular division have proprioceptors? where do the fibers go?

Answer 13

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

Question 14

what are the 3 parts of the spinal nucleus?

Answer 14

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

Question 15

what is jaw jerk?

Answer 15

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

Question 16

what is the VTTT? how is it formed?

Answer 16

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

Question 17

what is the VPM?

Answer 17

ventral posteromedial nucleus of the thalamus

Question 18

what does the VTTT process?

Answer 18

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

Question 19

what is the DTTT? how is it formed?

Answer 19

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

Question 20

what are the pain and temp afferents of the head?

Answer 20

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

Question 21

what is the corneal blink reflex?

Answer 21

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

Question 22

the response on the side stimulated is termed:

Answer 22

direct corneal reflex

Question 23

the response in the contralateral eye is termed:

Answer 23

consenual corneal reflex

Question 24

interruptions of the trigeminal nerve on one side:

Answer 24

abolishes BOTH the direct and the consensual response to stimulation

Question 25

a disorder affecting the facial nerve on one side:

Answer 25

touching the ipsilateral cornea does not evoke a direct response but does evoke a consensual response and also increases lacrimation

Question 26

lesions in the lateral part of the medulla or lower pons that damage the spinal tract of V frequently include:

Answer 26

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

Question 27

what is trigeminal neuralgia? what are trigger zones?

Answer 27

“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)??