The Trigeminal Sensory System Flashcards
What are the 3 divisions of the trigeminal nerve?
- opthalamic (V1)
- maxillary (V2)
- mandibular (V3)
What does CN V innervate?
- face
- head and also nasal sinuses
- inside of nose
- mouth (including teeth and gums)
- anterior 2/3 of tongue
Cell bodies of sensory neurons innervating head/face are found in the __________.
trigeminal ganglion (one on each side)
Trigeminal sensory systems for face are homologous to _________ and ___________ for the body.
- dorsal column medial lemniscus
- anterolateral system for body
Trigeminal nuclei:
- **Main (chief or principal) sensory nucleus **
-
Spinal trigeminal nucleus
- extending from pons down to cervical spinal cord
- homologous to spinal dorsal horn for body
- Caudal nucleus: extends from obex to spinal cord. Important nucleus for conveying pain and temp info from face, head
Main (chief or principal) sensory nucleus:
- Fine touch:
- located in pons
- homologous to dorsal column nuclei for body
Spinal trigeminal nucleus:
- **Pain and temp: **
- extending from pons down to cervical spinal cord
- homologous to spinal dorsal horn for body
-
Caudal nucleus: extends from obex to spinal cord.
- Important nucleus for conveying pain and temp info from face, head
Thalamic nuclei:
-
Ventral Posterior Medial nucleus
- both fine touch info, and pain and temp info go through VPM
- stay segregated
What is the primary afferent input for the trigeminal system?
Mechanoreceptor fibers enter from 3 branches of the Trigeminal nerve V
Describe the major pathway:
- Most fine touch mechanoreceptors synapse in the Chief (or Main) sensory nucleus of V
- on ipsilateral side
-
2nd order neurons then send off fibers that cross to the other side of the pons and form the Trigeminal Lemniscus
- joins the Medial Lemniscus
- Trigeminal lemniscus ascends to the Ventral Posterior Medial (VPM) nucleus
- terminates on to 3rd order thalamic neurons
Somatotopy of head and face in VPM:
- Tongue: medial
- Face: lateral
Minor pathway for some crude touch:
- A few mechanoreceptors:
- enter the pons but descend directly in the spinal tract of V to the spinal nucleus of V
- Then synapse
- 2nd order neurons:
- send fibers that cross the midline
- ascend in the trigeminothalamic tract to VPM
Minor pathway for oral cavity:
Dorsal trigeminal tract:
- A few mechanoreceptors:
- enter the pons
- synapse in Chief sensory nucleus
- 2nd order neurons don’t cross but ascend on the ipsilateral side to the ipsilateral VPM
- Conveys touch and pressure sensation from the oral cavity
- including teeth, mouth and gums
Function of 3rd order VPM thalamic neurons:
- send projections through the posterior limb of the internal capsule and corona radiata
- terminate in the lateral aspect of SI cortex
- near lateral fissure
Fibers carrying fine touch from the body and face enter tracts at __________ of the brainstem , but rostrally they _______ in ______________.
- different levels
- run together
- Medial/Trigeminal lemniscus tracts
- Body fibers enter at _______.
- Face fibers enter at _______.
- medulla
- pons
Trigeminothalamic tract: Primary Afferent Input:
Nociceptors from the face (3 branches of trigeminal nerve) enter in nerve V at pons
Nociceptors don’t synapse immediately but rather descend ___________ in the __________ and terminate in the ____________.
- ipsilaterally
- Spinal Trigeminal Tract
- spinal trigeminal nucleus of V
- Why does dirt under the contacts always hurt?
- Why is dental work painful?
- Some head tissues like tooth pulp and cornea are innervated only by nociceptors
Trigeminothalamic Tract: 2nd Order Neurons
- send axons that cross to other side of medulla
- ascend as the trigeminothalamic tract along side the anterolateral tracts ⇒ Ventral Posterior Medial (VPM) nucleus of the thalamus
Trigeminothalmaic Tract: 3rd order neurons
- In VPM project through the posterior limb of the internal capsule and corona radiata up to the lateral SI cortex
- Some others project to the reticular formation
What is trigeminal neuralgia?
- Neuralgia = pain along course of a nerve
- lancinating, severe pain that last seconds to minutes
- episodes brought on by chewing or shaving or touching trigger points in face
- Unknown etiology
- Fine touch, vibration facial sensation is normal
- Occurs in any or many: ear, eye, lips, nose, scalp, forehead, teeth, jaw
- Region of V2/V3 territory
-
Treatment: carbamazepine (anticonvulsant; acts on Na+ channels,
reduces excitability of neurons); sometimes antidepressants
Temperomandibular joint disorder (TMD):
- chronic pain localized at the temperomandibular joint or in muscles of mastication
- recurrent headaches
- ear pain
- Associated with teeth grinding, clenching at night, gum chewing, fingernail biting; trauma to jaw; stress
- Treatment: mouth guard, medications (NSAIDS); stress management
