Trigeminal Pathways

Question 1

Primary afferents (1st order neuron) of the trigeminal N extend from the cell bodies in the _____.

It attaches to the brainstem as two adjacent roots (large sensory and smaller motor) on the ____.

Answer 1

Trigeminal ganglion

Ventrolateral aspect of the pons

Question 2

Three sensory nuclei and one motor nucleus form a continuous cell column that extends from the _____ junction to rostral levels of the _____.

What are the four trigeminal nuclei?

Answer 2

Spinomedullary junction; mesencephalon/midbrain

Main sensory nucleus: forms an enlargement in the midpons slightly lateral motor nucleus

Trigeminal motor nucleus

Spinal nucleus: extends caudally form this level

Mesencephalic nucleus: extends rostrally all the way to the midbrain

Question 3

The trigeminal nuclei have segregated distribution of afferent fibers depending upon modalities.

What do they convey?

Answer 3

Main sensory nucleus: fibers conveying touch and pressure terminate here

Spinal nucleus: fibers carrying pain and temp info terminate here

Mesencephalic nucleus: proprioceptive afferent from muscles of mastication and the TMJ

Question 4

The main sensory nucleus is concerned with ____ and _____.

What are its two divisions?

Afferent somatotopic representation is inverted in the nucleus. Where are the three branches?

Answer 4

Discriminative tactile and proprioceptive sensations

Dorsomedial division: afferent input from oral cavity

Ventrolateral division: afferents from V1, V2, V3

V1: anterior
V2: in between
V3: posterior

Question 5

The main sensory nucleus relays discriminative tactile info from the head to the ____ of the thalamus.

The ventrolateral division projects to the contralateral VPM via the _____. This will be joined by fibers from the spinal nucleus of V.

Answer 5

Ventral posteromedial nucleus (VPM)

Trigeminal leminiscus (anterior trigeminothalmic tract)

Question 6

Dorsomedial division projects to the ipsilateral VPM via the ______. This ascends laterally to periaqueductal gray.

It terminates somatotopically within the VPM. The oral cavity is represented medially, external face laterally.

The tertiary axons from the VPM project via the _____ of the internal capsule to the ____.

Answer 6

Posterior dorsal trigeminothalmic tract (dorsal central trigeminal tract)

Posterior limb; primary somatosensory cortex

Question 7

Anterior trigeminothalmic tract contains the ____.

Posterior trigeminothalmic tract contains the ___.

Answer 7

Trigeminal lemniscus

Dorsal central trigeminal tract

Question 8

Spinal trigeminal nucleus receives info about ____ from the anterior half of the head.

Primary afferent fibers reach nucleus by turning caudally as they enter the pons to join the ____ and are positioned lateral to the nucleus.

Answer 8

Pain and temp

Spinal trigeminal tract

Question 9

The spinal trigeminal nucleus has three regions?

Answer 9

Pars/subnuclues caudalis: most caudal part extending from the spinal cord to the obex

Pars/subnucleus oralis: most rostral part, extending from the main sensory nucleus to pontomedullary junction

Pars/subnucleus interpolaris: located in between in rostral medulla

Question 10

Both the spinal trigeminal nucleus and tract extend caudally to about the _____.

They descend in the _____, a fiber tract lying immediately superficial to the nucleus.

The tract becomes continuous with ___ in the upper cervical cord.

Answer 10

3rd cervical segment

Spinal trigeminal tract

Lissauer’s tract

Question 11

The different parts of the ipsilateral half of the face are represented in the _____ and ___.

____ fibers are most posterior.
____ are most anterior.
____ are in between.

Answer 11

Caudal spinal trigeminal tract and nucleus

Mandibular division; ophthalmic division; maxillary division

Question 12

Each trigeminal division has a somatotopic arrangement with a rostral-caudal distribution. Fibers representing areas near the center of the face end near the ___.

Fibers representing areas toward the back of the head end in the ____.

Answer 12

Obex

Upper cervical cord

Question 13

Arrangement of the pars/subnuclues caudalis allows for a smooth transition of ____ with _____.

Answer 13

Spinal levels processing cutaneous info originating at the back of the head

Brainstem levels processing similar cutaneous info from face

Question 14

Trigeminal fibers ending in the cervical cord overlap ____ that represent adjacent areas of the skin.

Damage to the spinal trigeminal tract causes a pattern of sensory loss called ____.

The more caudal lesion causes ____. The more rostral lesion causes ____.

Answer 14

Spinal fibers

Onion-skin distribution

A larger area surrounding the mouth to be spared from sensory loss

Sensory loss that starts at the back of the head and converges on the mouth

Question 15

In the pars/subnucleus caudalis pathway, second order axons from the caudal nucleus decussate and ascend in the ____.

It terminates in the ____ of the thalamus.

The tertiary axons extend in the posterior limb of the ____ to the primary somatosensory cortex.

Answer 15

Anterior trigeminothalmic tract (trigeminal lemniscus)

Contralateral VPM

Internal capsule

Question 16

____ extends from the level of the entrance of V to the upper medulla. They receive _____ info from the central region of the face.

____ extends from the upper medulla to the level of the obex. It receives info from the peripheral region of the face.

They are involved in fx homologous to somatic fx of the spinal cord. They project fibers to the ____ through the _____ and carry tactile info projected to the _____.

Answer 16

Pars/subnucleus oralis; tactile info

Pars/subnucleus interpolaris

Cerebellum; inferior cerebellar peduncle

Contralateral VPM

Question 17

The _____ is comprised of pseudounipolar neurons. It is the only nucleus in the CNS and can be considered as displaced trigeminal ganglion cells.

It conveys unconscious proprioceptive and pressure info from ____.

Answer 17

Mesencephalic nucleus

Muscles of the oral region

Question 18

The mesencephalic nucleus projects to the _____. This allows _____ via the anterior/posterior trigeminothalmic tract.

Some axons terminate in the ____ to form the circuit for the ____ reflex.

Answer 18

Main sensory nucleus; conscious awareness of facial and oral proprioception

Trigeminal motor nucleus; jaw-jerk reflex

Question 19

____ innervates the muscles of the PA 1 such as the muscles of mastication, tensor tympani, tensor palatini, mylohyoid, anterior belly of digastric.

The nucleus is located in the ____; the fibers emerge as a separate motor root and are distributed peripherally with the ____.

Answer 19

Trigeminal motor nucleus

Midpons; mandibular division

Question 20

What are the two reflexes done by the trigeminal N?

Answer 20

Jaw-jerk

Corneal

Question 21

The afferent limb of the corneal reflex originates from _____ in the cornea.

Their fibers travel on the V1 with their cell bodies in the _____. They terminate in the ipsilateral ____.

Trigeminothalamic fibers send collaterals bilaterally into the ____.

Answer 21

Pain/touch receptors

Trigeminal ganglion; spinal trigeminal nucleus

Facial motor nucleus (efferent limb of the reflex)

Question 22

The jaw-jerk reflex is done by the afferent limb of the ____. Its peripheral process innervates the ____ and its central process synapses on a ____.

Answer 22

Mesencephalic trigeminal neuron

Masseter m spindle

Trigeminal motor neuron

Question 23

The mesencephalic nucleus via the spinal nucleus (pars interpolaris) gives what info via what?

The main sensory nucleus moderates what via what?

Both process what info?

Answer 23

Proprioceptive input from the jaw related to chewing/jaw placement; via the inferior cerebellar peduncle (restiform body)

The amount of secondary neurons that project to the anterior vermis of the cerebellum; superior cerebellar peduncle

Info regarding jaw placement during mastication; food texture and consistency are altered as it is chewed, changing the demands on jaw muscles

Question 23

What does a unilateral lesion in the trigeminal N cause?

Answer 23

Anesthesia and loss of general sensations in the trigeminal dermatomes

Loss of jaw-jerk reflex

Atrophy of muscles of mastication

Loss of ipsilateral and consensual corneal reflex

Question 23

What is alternating analgesia?

What are the effects in pts?

Answer 23

Brainstem lesions in the upper medullary may destroy primary fibers in the spinal trigeminal tract and secondary fibers in the spinal lemniscus

Pt have ipsilateral hemianalgesia of the face and contralateral hemianalgesia of the body

Question 23

What is alternating trigeminal hemiplegia?

Answer 23

Unilateral destruction of the trigeminal N and corticospinal tract in the pons

Ipsilateral trigeminal anesthesia and paralysis and contralateral spastic hemiplegia

Question 24

Lateral medullary (Wallenberg) syndrome is caused by the _____ that supplies the anterolateral system and the spinal trigeminal nucleus/tract.

A vascular lesion of this vessel causes what?

Answer 24

Posterior inferior cerebellar A

Contralateral loss of pain (hemianalgesia) and temp (hemithermoanesthesia) over the body with ipsilateral loss of these modalities over the face

Question 25

Tic douloureux (trigeminal neuralgia) produces ____ symptoms. Where?

What causes this?

Answer 25

Severe, episodic (paroxysmal) pain; “trigger zones”= the peripheral division of the maxillary or mandibular division ipsilaterally

Vascular compression of the trigeminal N root/ presence of microneuromas