5) Trigeminal Pathways Flashcards
Where does the trigeminal nerve attach to the brainstem?
Attaches to the brainstem as two adjacent roots (large sensory & smaller motor) on ventrolateral aspect of the pons
How many trigeminal nuclei are there and what are they?
What do they form?
Three sensory nuclei & one motor nucleus
- Main sensory nucleus (msT) forms an enlargement in the midpons, slightly lateral to motor nucleus
- Trigeminal motor nucleus (mT)
- Spinal nucleus extends caudally from this level
- Mesencephalic nucleus (mes) extends rostrally(all the way into the midbrain, as name implies)
Form a continuous cell column that extends from spinomedullary junction to rostral levels of mesencephalon/midbrain
The trigeminal nuclei have a segregated distribution of afferent fibers, depending upon modality… what are they?
Main sensory nucleus: fibers conveying touch & pressure terminate here
Spinal nucleus: fibers carrying pain & temperature information terminate here
Mesencephalic nucleus: proprioceptive afferents from muscles of mastication & the TMJ
What is the main sensory nucleus mainly concerned with? What are the two divisions and what do they receive?
Primarily concerned with discriminative tactile, & proprioceptive sensations
Dorsomedial division: afferent input from oral cavity
Ventrolateral division: afferents from V1, V2, V3 (these are inverted in the nucleus)
I would skip this card but…
If you want to know every path of the Main Sensory Nucleus… What are they?
Relay discriminative tactile information from the head to the ventral posteromedial (VPM) nucleusof the thalamus
Ventrolateral division projects to contralateral VPM via the trigeminal leminiscus(anterior trigeminothalamictract). Will be joined by fibers from the spinal nucleus of V
Dorsolateral division projects to ipsilateral VPM via the posterior dorsal trigeminothalamictract (dorsal central trigeminal tract). Ascends lateral to periaqueductal gray
Terminates somatotopically within the VPM. Oral cavity is represented medially, external face is represented laterally
Tertiary axons from VPM project via posterior limb of the internal capsuleto the primary somatosensory cortex
What does the spinal trigeminal nucleus receive?
There are three regions of the nucleus what are they?
Pain and temperature from anterior 1/2 of head.
- Pars/Subnucleus 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
Describe the mesencephalic nucleus.
Comprised of pseudounipolar neurons.
Only nucleus in the CNS
Can be considered displaced trigeminal ganglion cells
Conveys unconscious proprioceptive & pressure information from muscles of oral region
Projects to the main sensory nucleus (and spinal nucleus)
Permits the conscious awareness of facial & oral proprioception via the anterior/posterior trigeminothalamic tract
Some axons terminate in trigeminal motor nucleus → forms circuit for the jaw-jerk reflex
What are the two CN V reflexes?
The jaw-jerk reflex: Stretching the masseter (downward tap on chin), causes it to contract bilaterally. Afferent limb is a mesencephalic trigeminal neuron whose peripheral process innervates a masseter muscle spindle & whose central process synapses on a trigeminal motor neuron (efferent limb). Amplitude of the reflex is typically minor, but is enhanced after UMN damage
The corneal reflex: The afferent limb of the corneal reflex originates from pain/touch receptors in the cornea. Fibers travel on V1 & have their cell bodies in the trigeminal ganglion → terminate in ipsilateral spinal trigeminal nucleus. Trigeminothalamic fibers send collaterals bilaterally into the facial motor nucleus (efferent limb) of this reflex. In response to a stimulus that touches the cornea, the eyes blink
Name and describe the two trigeminocerebellar pathways.
Mesencephalic nucleus via Spinal nucleus (Pars interpolaris). Proprioceptive input from the jaw related to chewing/jaw placement. Via the inferior cerebellar peduncle (restiform body)
Main sensory nucleus: Moderate amount of secondary neurons project to the anterior vermis of the cerebellum. Via the superior cerebellar peduncle. Provides information regarding jaw placement during mastication, changes demands on jaw muscles based on food texture.
Three types of lesions of the trigeminal nerve… describe them.
Unilateral lesion, Alternating analgesia, alternating trigeminal hemiplegia
Unilateral lesion: 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
Alternating analgesia: Brainstem lesions in the upper medulla may destroy the primary fibers in the descending tract of V, & secondary fibers in the spinal lemniscus. Patients demonstrate ipsilateral hemianalgesia of the face & contralateral hemianalgesia of the body.
Alternating trigeminal hemiplegia: Unilateral destruction of the trigeminal nerve & CST in the pons. Ipsilateral trigeminal anesthesia & paralysis, & contralateral spastic hemiplegia
What artery supplies the territory of the anterolateral system and spinal trigeminal nucleus/tract?
Posterior inferior cerebellar artery.
Lesions of the posterior inferior cerebellar artery result in which syndrome?
Lateral medullary (Wallenberg) syndrome (posterior inferior cerebellar artery syndrome)
Describe Wallenberg (lateral medullary) syndrome
Contralateral loss of pain (hemianalgesia) & temperature (hemithermoanesthesia) over the body WITH Ipsilateral loss of these modalities over the face
Tic Douloureux (Trigeminal neuralgia)
Severe pain usually over maxillary or mandibular division ipsilaterally
Etiology of this condition is unknown, but vascular compression of the trigeminal nerve root and/or the presence of microneuromas are likely causes
