Trigeminal Nerve Pathway

Question 1

Describe the Pain Pathway from the Face.

Answer 1

Primary Axon - About 1/2 of fibers Descend ONLY in the Descending Tract of V and terminate in the subnucleus caudalis of the descending nucleus of V; Type A, Delta Fibers (Fast Pain); Descending root of V is continuous with the dorsolateral fasciculus of Lissauer in the spinal cord.

Secondary Axon - Decussate and ascend in the trigeminal lemniscus (TL); TL terminates in the Ventral Posterior Medial (VPM) nucleus of the dorsal thalamus.

Tertiary Axon - Goes to Inferior Portion of Postcentral Gyrus via the posterior limb of the internal capsule and corona radiata

Question 2

Describe the Crude Tactile Pathway from the Face.

Answer 2

Primary Axon - Terminates in Subnuclei rostralis and interpolaris

Secondary Axon - Trigeminal Lemniscus (aka anterior trigeminothalamic tract) and some fibers that DO NOT CROSS will travel in the ipsilateral Dorsal Central Trigeminal Tract (aka posterior trigeminothalamic tract); Terminates in the Ventral Posterior Medial (VPM) Nucleus

Tertiary Axon - Goes to Primary Somesthetic Cortex

Question 3

Describe the Precise Tactile and Proprioceptive Pathways from the Face.

Answer 3

Primary Axon - ASCEND ONLY in the short ascending root of V and will terminate in the Main Sensory Nucleus of V

Secondary Axon - Most of the secondary axons are going to travel with the ipsilateral dorsal central trigeminal tract - In the brainstem, these fibers travel with the medial lemniscus, and terminate in the ipsilateral VPM nucleus of the thalamus.
- Some fibers will DECUSSATE and travel with the Trigeminal Lemniscus

Tertiary Axon - VPM to post central gyrus via the posterior limb of the internal capsule

Question 4

Describe the Proprioceptive Pathways from the Face

Answer 4

Mesencephalic Nucleus contains the jaw-jerk reflex!

Question 5

Where does the subnucleus caudalis in the Pain pathway send fibers to?

What does it play a big role in?

Answer 5

Ascending Reticular Activating System (ARAS)

*** ARAS plays a big role in the GLASCOW COMA SCALE

Question 6

What is the function of Subnucleus Caudalis?

Answer 6

Pain and Temperature

Question 7

What is the function of the Descending Tract of V?

Answer 7

Pain and Temperature to the FACE

Question 8

What is going to carry the modality of Pain and Temperature from the BODY?

Answer 8

Spinal Lemniscus

Question 9

What are the two structures that send fibers to the Cerebellum?

Answer 9

1. Subnuclei rostralis and Interpolaris –> “Crude” Tactile information; Trigeminocerebell Fibers are going to course through the INFERIOR CEREBELLAR PEDUNCLE and enter the Anterior Vermis
2. Main Sensory Nucleus –> “Precise” Tactile and Proprioceptive information; T**rigeminocerebellar Tract is going to course through the SUPERIOR CEREBELLAR PEDUNCLE and enter the Anterior Vermis

Question 10

Describe the clinical presentation of:

Unilateral Lesion of the Trigeminal Nerve

Answer 10

1. Anesthesia and loss of general sensations in the trigeminal dermatomes (loss of sensation to 1/2 of the face!)
2. Loss of ipsilateral and consensual corneal reflex
3. Paralysis of muscles of mastication
   - Palpate the temporalis and masseter muscles
   - Atrophy of the muscles of mastication
   - Loss of jaw jerk reflexes

Question 11

Describe the clinical presentation of Alternating Trigeminal Analgesia.

Answer 11

*** Lesion of Descending Tract of V and Spinal Lemniscus

1. Ipsilateral hemianalgesia of the FACE
2. Contralateral Hemianalgesia of the BODY

Question 12

Describe the lesion pattern for:

Alternating Trigeminal Hemiplegia

Answer 12

*** Lesion of Trigeminal Nerve and Corticospinal Tract

1. Ipsilateral Trigeminal anesthesia and paralysis
2. Contralateral Spastic Hemiplesia

Question 13

Describe Trigeminal Neuralgia

Answer 13

Nuclei that are spontaneously DEPOLARIZING in the Subnucleus Caudalis

Question 14

Answer 14

1. E

2.

3.

4.