04 Trigeminal sensory system

Question 1

What part of brainstem does CN V come from

Answer 1

Ventrolateral part of Pons

Question 2

Trigeminal sensory tracts:

• tract name
• nucleus location
• which spinal tracts analogous to?

Answer 2

1. Trigeminal lemniscus tract.
   - Chief trigeminal sensory nucleus
   - PCML (light touch, proprioception, vibration, dental pressure)
2. Trigeminothalamic tract
   - Spinal trigeminal nucleus
   - Anterolateral (pain, temp)
3. Mesencephalic trigeminal nucleus
   - proprioception
4. Dorsal Trigeminal Tract–a minor pathway for oral cavity sense, some neurons are ipsilateral

Question 3

Major Pathway of Trigeminal fine touch

Answer 3

1. enter Pons to Chief nucleus V
2. decussate immediately to Trigeminal lemniscus, then to VPM
3. VPM to lateral SI cortex, through internal capsule

Question 4

How does the Minor pathway for crude touch based on trigeminal lemniscus pathway differ from fine touch?

Answer 4

-After entering pons to Chief nucleus V, 2nd neuron DESCENDS to caudal medulla before decussating and entering trigeminal lemniscus

Question 5

Dorsal Trigeminal Tract

Answer 5

-A minor tract for oral cavity. Neurons enter Pons, synapse at Chief nucelus V. Some neurons decussate, others stay ipsilateral to go to VPM. So, oral cavity is bilaterally innervated.

Question 6

Somatotopy of VPM and SI cortex

Answer 6

VPM: (lateral) face, oral cavity, tongue (medial)
SI: (lateral) tongue/pharynx, oral cavity, face (medial)

Question 7

Trigeminothalamic tract pathway

Answer 7

1. Nociceptors enter Pons, descend ipsilaterally to cervical cord to synapse in Spinal nucleus V
2. Decussate, then ascend via trigeminothalamic tract, next to spinothalamic tract, to VPM
3. VPM to SI cortex

Note: Just like anterolateral pathway, there are also neurons that ascend to reticular formation and midbrain instead of thalamus.

Question 8

Disorders of CN V

Answer 8

• Trigeminal neuralgia

- Temporomandibular joint disorder