Trigeminal Pathway

Question 1

3 divisions of Trigeminal N and what they innervate

Answer 1

1. ophthalmic–forehead and orbital regions
2. maxillary–malar and infraorbital
3. mandibular–cheek and lower jaw

Question 2

main sensory nucleus of V

Answer 2

• at the level of trigeminal N
• central processes of primary neurons in the trigeminal ganglion and mesencephalic nucleus terminate here
• receives precise tactile, crude tactile, and proprioceptive info from the face

Question 3

Pain and Temp from the Face

Answer 3

1. GSA fibers enter the brainstem with the trigeminal N
2. the fibers for pain and temp DESCEND ONLY win the descending tract/root o V
3. these fibers terminate in the sub nucleus caudalis of the descending tract of V
   
   • conveying A delta pain fibers and temp info from face
   • receives pain and temp from anterior 1/2 of head
4. secondary axons decussate and ascend in the trigeminal lemniscus
5. TL terminates in the ventral posterior medial (VPM) nucleus of the dorsal thalamus
6. axons from VPM project thru the posterior limb of the internal capsule to the post central gyrus (primary somesthetic_

Question 4

Trigemino-Reticulo-Thalamic Pathway

Answer 4

• C type pain fibers convey slow pain in the sub nucleus caudalis
  
  • these neurons project bilaterally to the brainstem reticular formation as trigeminoreticular fibers
  • these fibers go to the centromedian and reticular nuclei of the thalamus
• analogous to spinoreticulothalamic pathway–slow pain pathway in the SC

Question 5

crude tactile pathways from the face

Answer 5

1. axons enter the brainstem with the trigmeminal N and bifurcate to ascending and descending roots
   
   • the ascending fibers go to the main sensory nucleus–receives crude tactile from face
   • the descending fibers go to the subnuclei rostral and interpolaris of the descending nucleus of V–receives general tactile from face
2. secondary axons
   
   • most decussate and ascend in the trigeminal lemniscus (anterior trigeminothalamic tract) which is adjacent to the medial lemniscus
   • some remain uncrossed and ascend in the ipsilateral dorsal central trigeminal tract (DCTT) and travel with the medial lemniscus
3. both sets of fibers terminate in the ventral posterior medial (VPM) nucleus of the dorsal thalamus
4. tertiary axons projet to the posterior limb of internal capsule to the primary somesthetic cortex

Question 6

precise tactile pathway from face

Answer 6

1. fibers come in with the trigeminal N
2. fibers ASCEND ONLY in the short ascending root of V
3. terminate in the main sensory nucleus of V–for precise tactile info
4. secondary axons
   
   • most fibers go to the ipsilateral dorsal central trigeminal tract and travel with the medial lemniscus
   • some fibers decussate and ascend in the trigeminal lemniscus
5. both sets terminate in the ventral posterior medial nucleus of the dorsal thalamus
6. fibers from VPM go thru the posterior limb of the internal capsule to the primary somesthetic cortex

Question 7

proprioceptive pathway from face

Answer 7

1. cell body of the primary neuron is in the mesencephalic nucleus
   
   • only nucleus in CNS with pseudo unipolar neurons
2. central process terminates in main sensory nucleus
3. most fibers ascend in the ipsilateral dorsal central trigeminal tract and a few in the contralateral trigeminal lemniscus
4. terminate in the ventral posterior medial nucleus
5. goes to the primary somesthetic cortex

Question 8

mesencephalic nucleus

Answer 8

• involves with proprioception of the face
• receives unconscious proprioceptive and pressure info from Ms of the head and oral region
• peripheral process of pseudo unipolar primary neurons course with the mandibular N–>pass thru the trigeminal ganglion–>enters brainstem with trigeminal N–>ascend towards the mesencephalic nucleus in mesencephalic root of V

Question 9

jaw jerk reflex

Answer 9

• rapid depression of the chin results in reflex clenching of the teeth
• invovles neuromuscular spindles in the masseter M–>masseteric N–>mesenephlaic nucleus–>motor nucleus of V–>masseteric N–>MEP

Question 10

trigeminocerebellar tract

Answer 10

• crude tactile:
  
  • subnuclei rostralis and interpolaris–>trigeminocerebellar fibers to the anterior vermis–>ipsilateral inferior cerebellar peduncle
• precise tactile and proprioception:
  
  • main sensory nucleus–>superior cerebellar peduncle–>anterior vermis

Question 11

unilateral lesions of the trigeminal N:

Answer 11

• anesthesia and loss of general sensations in trigeminal dermatomes
• loss of jaw jerk reflex
• atrophy of the Ms of mastication
• loss of ipsilateral and consensual corneal reflex

Question 12

alternating anesthesia

Answer 12

• brainstem lesions in the upper medulla may destroy the primary fibers in the descending tract and V and secondary fibers in the spinal lemniscus
• pts show ipsilateral hemianalgesia (loss of pain and temp) of the face and contralateral hemianalgesia to the body

Question 13

alternating trigeminal hemiplegia

Answer 13

• result of unilateral destruction of the trigeminal N and corticospinal tract in the pons
• results in ipsilateral trigeminal anesthesia and paralysis and contralateral spastic hemiplegia

Question 14

trigeminal neuralgia

Answer 14

• cutaneous region in the head may initiate abnormal epileptic like discharges from the sub nucleus caudal its
• intractable, lacerating facial pain which follows distribution of the trigeminal N
• treated with anticonvulsant meds, cryosurgery of trigeminal ganglion or trigeminal or medullary tractotomy