Lecture 5: Trigeminal Pathways Flashcards
The trigeminal nerve is the main sensory nerve for the ______ and innervates which muscles?
- Main sensory nerve for the head
- Innervates muscles of mastification
Where do the primary afferents of the trigeminal nerve attach to brainstem?
- 2 adjacent roots
- Large sensory and small motor
- Ventrolateral aspect of the pons
What are the 4 Trigeminal nuclei?
- Main sensory nucleus (msT): forms an enlargement in the midpons, slightly lateral to motor nucleus
- Trigeminal motor nucleus (mT): controls motor efferent
- Spinal nucleus extends caudally from this level
- Mesencephalic nucleus (mes): extends rostrally (all the way into midbrain)
Fibers conveying what information terminate in the Main Sensory Trigeminal nucleus?
Touch and pressure
Fibers conveying what information terminate in the Spinal Trigeminal nucleus?
Pain and temperature from anterior 1/2 of head
Fibers conveying what information terminate in the Mesencephalic Trigeminal nucleus?
Proprioceptive afferents from muscles of mastification and the TMJ
What kind of afferents do the dorsomedial and ventrolateral division of the Trigeminal Main Sensory nucleus receive?
Dorsomedial division: afferent input from oral cavity
Ventrolateral division: afferents from V1, V2, V3
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?
- Afferent somatotopic representation is inverted in the nucleus
- V1 is anterior
- V2 is sandwiched in between
- V3 is posterior
Where does the Ventrolateral Division of the Trigeminal Main Sensory nucleus project and via what; will be joined by fibers from where?
- 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
Where does the Dorsomedial Division of the Trigeminal Main Sensory nucleus project and via what?
- To the ipsilateral VPM via the:
- Posterior dorsal trigeminothalamic tract (dorsal central trigeminal tract)
*Carries afferents from the oral cavity
After receiving seconday afferents in the Trigeminal pathway where do the tertiary axons from the VPM project and via what?
- To the primary somatosensory cortex
- Via the posterior limb of the internal capsule
How do primary afferent fibers reach the Spinal Trigeminal Nucleus and what do they join?
- By turning caudally as they enter the pons
- Join the spinal trigeminal tract (aka descending tract of V)
What are the 3 regions of the Spinal Trigeminal Nucleus?
- 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
What does the spinal trigeminal tract (descending tract of V) become continous with?
Lissauer’s tract in the upper cervical cord
How are the mandibular, opthalmic, and maxillary divisions of the ipsilateral half of face represented systematically in the caudal spinal trigeminal tract AND nucleus?
- Mandibular division fibers are most posterior
- Opthalmic division fibers are most anterior
- Maxillary division fibers are in between
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?
- 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
The inverted arrangement in the Pars/Subnucleus Caudalis allows for smooth transition of what?
- Spinal levels processing cutaneous information originating at the back of the head with:
- Brainstem levels processing similar cutaneous information from the face
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?
- Trigeminal fibers overlap these spinal fibers
- Characteristic pattern of sensory loss when spinal trigeminal tract is damaged, onion-skin distribution
The Mesencephalic Trigeminal nucleus is composed of what type of neurons and conveys what type of information?
- Comprised of pseudounipolar neurons
- Conveys unconcious proprioceptive and pressure information from muscles of the oral region
The Mesencephalic Trigeminal Nucleus projects to which nucleus?
Projects to the main sensory nucleus (and spinal nucleus)
Which Trigeminal nuclei permits the conscious awarness of facial and oral proprioception via the anterior/posterior trigeminothalamic tract?
Mesencephalic Trigeminal Nucleus
The Trigeminal Motor Nucleus innervates which pharyngeal arch muscles and what are they?
- 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
The Trigeminal Motor Nucleus is located where; adjacent to what nucleus?
- Located in the midpons
- Adjacent to the main sensory nucleus
The motor root fibers of the Trigeminal Motor Nucleus pass through which foramen?
Foramen Ovale
What is the jaw-jerk reflex and what are the afferents; when is the amplitude of this reflex enhanced?
- 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
The afferent fibers of the corneal reflex travel on which trigeminal division and terminate where; what is the efferent component?
- 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
The cerebellum receives inputs via the Trigeminocerebellar pathway via what 2 nuclei, which is the main, and what kind of information is being relayed?
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!
The PICA supplies what important components of the Trigeminal pathway; what does a lesion of this vessel cause?
- Territory of anterolateral system AND spinal trigeminal nucleus/tract
- Lesions produce lateral medullary (Wallenberg) syndrome (PICA syndrome)
What is the common presentation of someone with Lateral Medullary (Wallenberg) Syndrome?
- Contralateral loss of pain (hemianaglesia) and temperature (hemithermoanesthesia) over the body
WITH
- Ipsilateral loss of these modalities over the face
