Trigeminal Pathway

Question 1

The sensory and motor roots of V pierce the ______ _______ _______.

Answer 1

middle cerebellar peduncle just posterolateral to the pons

Question 2

Describe the Trigeminal Nuclei

Answer 2

primary neurons ascend or descend conveying genreal tactile info. from the main sensory nucleus and the subnuclei rostralis and interpolaris of the descending nucleus of V

ascending fibers: precise discriminative from face
Mesencephalic tract of V: proprio fiber
descending fibers: pain/temp

Question 3

What are the four nuclei of the trigeminal nerve?

Answer 3

Three form the trigeminal sensory complex and one form the motor nucleus

1. main sensory nucleus
2. Descending Nucleus of V
3. Mesencephalic of V
4. Trigeminal Motor Nucleus

Question 4

Describe the main sensory nucleus of V.

Answer 4

analogous to the nuclei gracilis and cuneatus.
located at the local of the trigeminal nerve
The central processes of 1 neurons in the trigeminal ganglion and the mesencephalic nucleus terminate in the main sensory nucleus

function: precise tactile, crude tactile, and proprio info. from the face

Question 5

Describe the Descending Nucleus of V.

Answer 5

analogous to the dorsolateral fasciculus of Lissauer in the spinal cord
Functions: convey pain/temp.
3 subdivision:
1. Subnucleus Rostralis: tactile info. from the central region of the face
2. Subnucleus Interpolaris: receives info. from the peripheral region of the face
3. Subnulcues Caudalis: receives pain/temp info from the anterior 1/2 of the head

Question 6

Describe the mesencephalic nucleus.

Answer 6

nucleus is comprised of pseudounipolar neurons

Function: convey unconscious proprio/pressure info. from muscles of the head and oral region

Question 7

Describe the Trigeminal Motor Nucleus.

Answer 7

innervates muscles derive from mesechymal cell in the first branchial arch

Question 8

Describe the pain pathway from the face.

Answer 8

1 axons: 1/2 only descend in the descending root of V, and terminate in the subnucleus caudalis of the descending nucleus of V.
2 axons: subnucleus caudalis receives pain/temp info. from the anterior 1/2 of the head; decussate and ascend in the trigeminal lemniscus
3 axons: from the ventral posterior medial nucleus of the dorsal thalamus. theses axons project to the primary somethetic cortex via the posterior limb of the internal capsule

Question 9

Describe Trigemino-reticulo-thalamic Pathway

Answer 9

‘C’ fiber pain convey “slow” pain info. to the subnucleus caudalis; these fiber project bilaterally to the brainstem reticular formation as trigeminoreticular fibers

analogous to the spino-reticulo-thalamic pathway

the trigeminal input into the RF facilitates the ascending rreticular activating system (ARAS): arousal and alertness

Question 10

What is the crude tactile Pathway from the Face.

Answer 10

1 axons: enter brainstem then bifurcate conveying general tactile info. to both the main sensory nucleus and the subnuclei and interpolaris of the descending nucleus of V
2 axons: axons decussate and ascend in the trigeminal lemniscus (anterior trigeminothalamic tract) terminating in the VPM
uncrossed axon from the ipsilateral dorsal central trigeminal tract (DCTT)
3 axon: start in the VPM and project to the primary somesthetic cortex via the posterior limb of the internal capsule

Question 11

What is the Precise Tactile Pathway from the Face?

Answer 11

1. main sensory nucleus
2. most fibers ascend in the ipsilateral dorsal central trigeminal tract
3. VPM
4. Primary Somethetics Cortex

Question 12

What is the Proprioceptive Pathway from the Face?

Answer 12

mesencephalic nucleus receives unconscious proprio/pressure info. from muscles of the head and oral regions
1 axons: course w/ the mandibular n. who cell body are located in the mesencephalic root of V; the axon synapse in the main sensory nucleus

(connection permits the conscious awareness of facial and oral proprio via the trigeminal lemniscus

3. VPM
4. Primary Somesthetic Cortex

Question 13

Describe the Jaw-Jerk (Masseteric) Reflex.

Answer 13

stimulus: rapid depression of the chin
receptor: NMS
afferent: masseteric n.
Nucleus: mesencephalic nucleus to the motor nucleus of V (efferent)
Efferent: masseteric n.
effector: the motor end-plate

Question 14

What is the Trigemminocerebellar Pathways?

Answer 14

Trigeminocerebellar Tract
only the subnuclei rostralis and interpolaris project to the cerebellum; the subnuclei projects trigeminocerebellar fibers to the anterior vermis via the ipilateral cerebellar peduncle conveyng crude tactile info.

some 2 neurons in the main sensory nucleus project to the anterio vermis of the cerebellum via the superior cerebellar peduncle conveying precise tactile and proprio info.

Question 15

How does a unilateral lesion of the trigeminal Nerve present?

Answer 15

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

Question 16

How and Why does a alternating analgesia present?

Answer 16

brainstem lesions in the upper medulla may destroy the primary fibers in the descending tract of V and the 2 fiber in the spinal lemniscus:
ipsilateral hemianalgesia of the face
contralateral hemianalgesia of the body

Question 17

How and Why does Alternating Trigeminal Hemiplegia present?

Answer 17

unilateral destruction of the trigeminal nerve and corticospinal tract in the pons results in ipsilateral trigeminal anesthesia and paralysis, and contralateral spastic hemiplegia

Question 18

How and why does Trigmeinal Neuralgia present?

Answer 18

trigger zone in the head has “epileptic-like” discharges from the subnucleus caudalis
intractable, lacerating facial pain, which follows the distribution of the affected division of CN V