Lecture 5: Trigeminal Pathways

Question 1

The trigeminal nerve is the main sensory nerve for the ______ and innervates which muscles?

Answer 1

• Main sensory nerve for the head
• Innervates muscles of mastification

Question 2

Where do the primary afferents of the trigeminal nerve attach to brainstem?

Answer 2

• 2 adjacent roots
• Large sensory and small motor
• Ventrolateral aspect of the pons

Question 3

What are the 4 Trigeminal nuclei?

Answer 3

1. Main sensory nucleus (msT): forms an enlargement in the midpons, slightly lateral to motor nucleus
2. Trigeminal motor nucleus (mT): controls motor efferent
3. Spinal nucleus extends caudally from this level
4. Mesencephalic nucleus (mes): extends rostrally (all the way into midbrain)

Question 4

Fibers conveying what information terminate in the Main Sensory Trigeminal nucleus?

Answer 4

Touch and pressure

Question 5

Fibers conveying what information terminate in the Spinal Trigeminal nucleus?

Answer 5

Pain and temperature from anterior 1/2 of head

Question 6

Fibers conveying what information terminate in the Mesencephalic Trigeminal nucleus?

Answer 6

Proprioceptive afferents from muscles of mastification and the TMJ

Question 7

What kind of afferents do the dorsomedial and ventrolateral division of the Trigeminal Main Sensory nucleus receive?

Answer 7

Dorsomedial division: afferent input from oral cavity

Ventrolateral division: afferents from V₁, V₂, V₃

Question 8

What occurs to afferent somatotopic representation of V1, V2, and V3 in the Trigeminal Main Sensory nucleus and what portion is each division located on?

Answer 8

• Afferent somatotopic representation is inverted in the nucleus
• V1 is anterior
• V2 is sandwiched in between
• V3 is posterior

Question 9

Where does the Ventrolateral Division of the Trigeminal Main Sensory nucleus project and via what; will be joined by fibers from where?

Answer 9

• To contralateral VPM via the:
• Trigeminal leminiscus (anterior trigeminothalamic tract)
• Joined by fibers from the spinal nucleus of V

*Carrying afferents from V1, V2, and V3

Question 10

Where does the Dorsomedial Division of the Trigeminal Main Sensory nucleus project and via what?

Answer 10

• To the ipsilateral VPM via the:
• Posterior dorsal trigeminothalamic tract (dorsal central trigeminal tract)

*Carries afferents from the oral cavity

Question 11

After receiving seconday afferents in the Trigeminal pathway where do the tertiary axons from the VPM project and via what?

Answer 11

• To the primary somatosensory cortex
• Via the posterior limb of the internal capsule

Question 12

How do primary afferent fibers reach the Spinal Trigeminal Nucleus and what do they join?

Answer 12

• By turning caudally as they enter the pons
• Join the spinal trigeminal tract (aka descending tract of V)

Question 13

What are the 3 regions of the Spinal Trigeminal Nucleus?

Answer 13

1. Pars/Subnucleus caudalis: most caudal part, extending from the spinal cord to the obex
2. Pars/Subnucleus oralis: most rostral part, extending from the main sensory nucleus to pontomedullary junction
3. Pars/Subnucleus interpolaris: located in between, in rostral medulla

Question 14

What does the spinal trigeminal tract (descending tract of V) become continous with?

Answer 14

Lissauer’s tract in the upper cervical cord

Question 15

How are the mandibular, opthalmic, and maxillary divisions of the ipsilateral half of face represented systematically in the caudal spinal trigeminal tract AND nucleus?

Answer 15

• Mandibular division fibers are most posterior

- Opthalmic division fibers are most anterior

• Maxillary division fibers are in between

Question 16

Each trigeminal division has a somatotopic arrangement with a rostral-caudal distribution, where are the fibers near the center of the face and those toward the back of the head?

Answer 16

• Fibers representing areas near the center of face end near the Obex
• Fibers representing areas towards the back of head end in the upper cervical cord

Question 17

The inverted arrangement in the Pars/Subnucleus Caudalis allows for smooth transition of what?

Answer 17

• Spinal levels processing cutaneous information originating at the back of the head with:
• Brainstem levels processing similar cutaneous information from the face

Question 18

What happens between the Trigeminal fibers ending in the cervical cord and the spinal fibers that represent adjacent areas of skin; why is this clinically relevant?

Answer 18

• Trigeminal fibers overlap these spinal fibers
• Characteristic pattern of sensory loss when spinal trigeminal tract is damaged, onion-skin distribution

Question 19

The more caudal the lesion to the Spinal Trigeminal tract is, what occurs with sensory loss?

Answer 19

Larger the area surrounding the mouth that is spared from sensory loss

Question 20

The more rostral the lesion (into brainstem) of the Spinal Trigeminal tract is, what occurs with sensory loss?

Answer 20

Can cause sensory loss that starts at the back of the head and converges on the mouth

Question 21

Explain the path of second-order neurons from the Pars/Subnucleus Caudalis pathway?

Answer 21

• Second-order neurons deucssate and ascend in the anterior trigeminothalamic tract
• Terminate in the contralateral VPM of the thalamus

- Tertiary axons extend in posterior limb of the internal capsule —> primary somatosensory cortex

Question 22

Pain fibers in the Trigemino-reticulo-thalamic pathway convey what type of pain information to where?

Answer 22

“Slow” pain information to the caudal nucleus project bilaterally to the brainstem reticular formation (RF) as trigeminoreticular fibers

Question 23

Trigeminal input from the reticular formation (RF) facilitates the ascending reticular activating system (ARAS), and plays an important role in?

Answer 23

• Arousal and alertness
• RF is a set of connected nuclei responsible for wakefulness and sleep-wake transition
• ARAS is a part of the RF and is mostly composed of various nuclei in the thalamus

Question 24

The Pars/subnucleus oralis extends from where to where; receives what kind of information?

Answer 24

• From level of the entrance of V to the upper medulla
• Receives tactile information from the central region of face

Question 25

The Pars/subnucleus interpolaris extends from where to where; receives what type of information?

Answer 25

- Upper medulla to the level of the obex - Receives information from the **peripheral region** of the **face**

Question 26

The Pars/subnucleus Oralis and Interpolaris have what 2 functions that are homologous to somatic functions of the SC?

Answer 26

1. Project fibers to the cerebellum (through the inferior cerebellar peduncle) 2. Carry tactile information project to the contralateral VPM

Question 27

The Mesencephalic Trigeminal nucleus is composed of what type of neurons and conveys what type of information?

Answer 27

- Comprised of **pseudounipolar neurons** - Conveys **unconcious proprioceptive** and **pressure** information from **muscles** of the **oral region**

Question 28

The Mesencephalic Trigeminal Nucleus projects to which nucleus?

Answer 28

Projects to the **main sensory nucleus (and spinal nucleus)**

Question 29

Which Trigeminal nuclei permits the conscious awarness of facial and oral proprioception via the anterior/posterior trigeminothalamic tract?

Answer 29

Mesencephalic Trigeminal Nucleus

Question 30

The Trigeminal Motor Nucleus innervates which pharyngeal arch muscles and what are they?

Answer 30

- Pharyngeal Arch 1 muscles - Muscles of mastification (masseter, temporalis, medial and lateral pterygoid) - Also the tensor tympani, tensor palati, mylohyoid, and the anterior belly of digastric

Question 31

The Trigeminal Motor Nucleus is located where; adjacent to what nucleus?

Answer 31

- Located in the **midpons** - Adjacent to the **main sensory nucleus**

Question 32

The motor root fibers of the Trigeminal Motor Nucleus pass through which foramen?

Answer 32

Foramen Ovale

Question 33

What is the jaw-jerk reflex and what are the afferents; when is the amplitude of this reflex enhanced?

Answer 33

- Stretching of the masseter (downward tap on chin), causes it to contract bilaterally - Afferent limb is a **mesencephalic trigeminal neuron** whose peripheral process innervates a massester muscle spindle and central process synapses on a trigeminal motor neuron (efferent limb) - Amplitude of reflex is typically minor, **enhanced** after **UMN damage**

Question 34

The afferent fibers of the corneal reflex travel on which trigeminal division and terminate where; what is the efferent component?

Answer 34

- Fibers travel on **V1** and have their cells bodies in the trigeminal ganglion --\> terminate in ipsilateral spinal trigeminal nucleus - Trigeminothalamic fibers send collateral bilaterally into the **facial motor nucleus** (efferent limb) of this reflex

Question 35

The cerebellum receives inputs via the Trigeminocerebellar pathway via what 2 nuclei, which is the main, and what kind of information is being relayed?

Answer 35

1) Fibers going from the **Mesencephalic nucleus** to the **Pars interpolaris** of the **Spinal Trigeminal nucleus.** Then relayed to the cerebellum via the **inferior cerebellar peduncle (restiform body)** 2) Some fibers also being relayed to cerebellum via the **Main Sensory nucleus** - Sends proprioceptive input from the jaw related to **chewing/jaw placement** - Necessary for changing the demand on jaw muscles as food texture/consistency is altered as we chew!

Question 36

A unilateral lesion of the Trigeminal nerve will produce what?

Answer 36

- Anesthesia and loss of general sensation in the trigeminal dermatomes - Loss of jaw jerk reflex - Atrophy of the muscles of mastification - Loss of ipsilateral and consensual corneal reflex

Question 37

What is Alternating anaglesia and how is it related to Trigeminal nerve?

Answer 37

- Brainstem lesions in the upper medulla may destroy primary fibers in the descending tract of V, and secondary fibers in the spinal lemniscus - Patients demonstrate **ipsilateral hemianaglesia of the face** and **contralateral hemianaglesia of the body**

Question 38

What is Alternating trigeminal hemiplegia?

Answer 38

- Unilateral destruction of the trigeminal nerve and CST in the pons - **Ipsilateral trigeminal anesthesia and paralysis** + **contralateral hemiplegia**

Question 39

The PICA supplies what important components of the Trigeminal pathway; what does a lesion of this vessel cause?

Answer 39

- Territory of **anterolateral system** AND **spinal trigeminal nucleus/tract** - Lesions produce **lateral medullary (Wallenberg) syndrome (PICA syndrome)**

Question 40

What is the common presentation of someone with Lateral Medullary (Wallenberg) Syndrome?

Answer 40

- **Contralateral** loss of pain (hemianaglesia) and temperature (hemithermoanesthesia) over the **body** **WITH** - **Ipsilateral** loss of these modalities **over the face**

Question 41

Vascular compression of the Trigeminal nerve root can lead to Tic Douloureux (Trigeminal neuralgia); what is seen in this condition?

Answer 41

- **Severe, episodic "paroxysmal" pain** usually restricted to the peripheral distribution of the **maxillary or mandibular division ipsilaterally** - Presence of "**trigger zones**," which on the most gentle stimulation (light breeze, brush with a wisp of cotton) produces **stabbing** **pain** onone side of the face

Question 42

The 3 sensory nuclei and one motor nucleus of the Trigeminal system form a continous cell column that extends from ________ to rostral levels of \_\_\_\_\_\_\_\_\_\_\_

Answer 42

The 3 sensory nuclei and one motor nucleus of the Trigeminal system form a continous cell column that extends from **spinomedullary junction** to rostral levels of **mesencephalon/midbrain**