CN V: Trigeminal Nerve

Question 1

What type of axons are in the trigeminal nerve?

Answer 1

General Somatic Afferent: Spinal and Main sensory nuclei

Special Visceral Efferent: Tregeminal motor nucleus

Question 2

What is the major function of the trigeminal nerve?

Answer 2

Transmit tactile, porprioceptive, pain and temp from head to cortex (also cerebellum and RF)

Question 3

What are the three divisions of CN V?

Answer 3

Ophthalmic (V1): upper face; sensory
Maxillary (V2): middle face; sensory
Mandibular (V3): lower face; sensory and motor

Question 4

Which division is the only one with efferent axons?

Answer 4

V3 - Mandibular

Question 5

Which nucleus is found in the midbrain?

Answer 5

Trigeminal mesencephalic nucleus

Question 6

Which nucleus is found in the pons?

Answer 6

1. Trigeminal main/principal sensory nucleus
2. Trigeminal motor nucleus
3. Trigeminal spinal nucleus

Question 7

Which nucleus extends from the pons down into the midbrain?

Answer 7

Trigeminal spinal nucleus

Question 8

1. Where do the axons from the trigeminal motor nucleus terminate?
2. What would a lesion cause?

Answer 8

1. Muscles of Mastication and tensor twins

2. Weakened jaw closure and open jaw will lean towards affected side

Question 9

Describe path of an impulse coming into and going out of the mesencephalic nucleus.

Answer 9

V2 and V3 receptors -> mesencephalic nucleus -> axons to supratrigeminal nucleus and motor nucleus -> out to control vertical dimension of occlusion

Question 10

What is a major function of the mesencephalic nucleus?

Answer 10

Sense the position and tension of the jaw and muscles, and tell the motor nucleus so it can change vertical dimension of occlusion appropriately

Question 11

What would a lesion to the mesencephalic nucleus cause?

Answer 11

Inability to sense or control VDO

Question 12

What is the tract associated with the spinal nucleus after crossing the midline?

Answer 12

Tregeminothalamic tract

Question 13

What is the tract for the combination of main/principle nucleus axons and spinal nucleus axons after crossing the midline?

Answer 13

Trigeminal lemniscus

Question 14

Describe the path of the trigeminal lemniscus?

Answer 14

Axons from spinal nucleus and main/principle nucleus cross midline and combine -> thalamus VPM -> postcentral gyrus

Question 15

On the postcentral gyrus, what parts of the body are represented in which areas? (Medial to lateral)

Answer 15

Lower limb -> upper limb -> upper face -> lower face

The face accounts for as much area as all the limbs and trunk combined!!

Question 16

What is the main function of the main/principle nucleus?

Answer 16

Receives TOUCH and VIBRATION from face, head, oral cavity, and meninges.

Question 17

What happens to the crossed fibers from the main/principle nucleus?

Answer 17

They join the medial lemniscus and go to opposite VPM and postcentral gyrus

Question 18

What happens to the uncrossed fibers from the main/principle nucleus?

Answer 18

Become dorsal trigeminal tract goes to same side VPM and postcentral gyrus

Represents inside of mouth

Question 19

What function does the spinal trigeminal nucleus serve?

Answer 19

PAIN, crude touch, and TEMPERATURE from the face, oral cavity and meninges

Question 20

Describe the positioning of the spinal trigeminal nucleus and tract?

Answer 20

Nucleus is gray matter posterolateral (just lateral to fasciculus cuneatus) with tract between nucleus and border

Question 21

Describe the pathway of afferent neurons to the spinal trigeminal nucleus.

Answer 21

Come in at midpons and descend through spinal trigeminal tract to nucleus in caudal medulla

Question 22

Describe the pathway of efferent neurons in the spinal trigeminal nucleus?

Answer 22

Afferent synapse in the nucleus with efferent -> efferent cross midline -> join spinothalmic tract -> VPM -> postcentral gyrus

Question 23

Where is the spinalthalmic tract in relation to the medial lemniscus?

Answer 23

Typically just lateral and slightly posterior in the midbrain

Question 24

Of the three sensory nuclei which has lightly myelinated fibers?

Answer 24

Spinal nucleus

Question 25

What are the functions of the three sensory nuclei?

Answer 25

Mesencephalic - proprioception
Main/principal - discriminative touch
Spinal nucleus - pain and temperature

Question 26

In the event of an injury to the pars caudalis what would a more caudal injury result in?

Answer 26

Peripheral loss of pain and temp

Rostral = peripheral and central face

Question 27

What is trigeminal neuralgia?

Answer 27

Brief episodes of extreme pain to area of CN V distribution (mostly mandibular)

Question 28

How could surgery help trigeminal neuralgia?

Answer 28

Cutting nerve root, introducing lesion in trigeminal ganglion

Result: lose all tactile and pain to area

Question 29

The most effective CN V neuralgia treatment would be to cut afferents just slightly caudal to obex, what would be the result and risk?

Answer 29

Result: keep tactile but lose pain over half of face
Risk: close to medullary cardiovascular and respiratory centers