CN V: Trigeminal Nerve Flashcards
What type of axons are in the trigeminal nerve?
General Somatic Afferent: Spinal and Main sensory nuclei
Special Visceral Efferent: Tregeminal motor nucleus
What is the major function of the trigeminal nerve?
Transmit tactile, porprioceptive, pain and temp from head to cortex (also cerebellum and RF)
What are the three divisions of CN V?
Ophthalmic (V1): upper face; sensory
Maxillary (V2): middle face; sensory
Mandibular (V3): lower face; sensory and motor
Which division is the only one with efferent axons?
V3 - Mandibular
Which nucleus is found in the midbrain?
Trigeminal mesencephalic nucleus
Which nucleus is found in the pons?
- Trigeminal main/principal sensory nucleus
- Trigeminal motor nucleus
- Trigeminal spinal nucleus
Which nucleus extends from the pons down into the midbrain?
Trigeminal spinal nucleus
- Where do the axons from the trigeminal motor nucleus terminate?
- What would a lesion cause?
- Muscles of Mastication and tensor twins
2. Weakened jaw closure and open jaw will lean towards affected side
Describe path of an impulse coming into and going out of the mesencephalic nucleus.
V2 and V3 receptors -> mesencephalic nucleus -> axons to supratrigeminal nucleus and motor nucleus -> out to control vertical dimension of occlusion
What is a major function of the mesencephalic nucleus?
Sense the position and tension of the jaw and muscles, and tell the motor nucleus so it can change vertical dimension of occlusion appropriately
What would a lesion to the mesencephalic nucleus cause?
Inability to sense or control VDO
What is the tract associated with the spinal nucleus after crossing the midline?
Tregeminothalamic tract
What is the tract for the combination of main/principle nucleus axons and spinal nucleus axons after crossing the midline?
Trigeminal lemniscus
Describe the path of the trigeminal lemniscus?
Axons from spinal nucleus and main/principle nucleus cross midline and combine -> thalamus VPM -> postcentral gyrus
On the postcentral gyrus, what parts of the body are represented in which areas? (Medial to lateral)
Lower limb -> upper limb -> upper face -> lower face
The face accounts for as much area as all the limbs and trunk combined!!
What is the main function of the main/principle nucleus?
Receives TOUCH and VIBRATION from face, head, oral cavity, and meninges.
What happens to the crossed fibers from the main/principle nucleus?
They join the medial lemniscus and go to opposite VPM and postcentral gyrus
What happens to the uncrossed fibers from the main/principle nucleus?
Become dorsal trigeminal tract goes to same side VPM and postcentral gyrus
Represents inside of mouth
What function does the spinal trigeminal nucleus serve?
PAIN, crude touch, and TEMPERATURE from the face, oral cavity and meninges
Describe the positioning of the spinal trigeminal nucleus and tract?
Nucleus is gray matter posterolateral (just lateral to fasciculus cuneatus) with tract between nucleus and border
Describe the pathway of afferent neurons to the spinal trigeminal nucleus.
Come in at midpons and descend through spinal trigeminal tract to nucleus in caudal medulla
Describe the pathway of efferent neurons in the spinal trigeminal nucleus?
Afferent synapse in the nucleus with efferent -> efferent cross midline -> join spinothalmic tract -> VPM -> postcentral gyrus
Where is the spinalthalmic tract in relation to the medial lemniscus?
Typically just lateral and slightly posterior in the midbrain
Of the three sensory nuclei which has lightly myelinated fibers?
Spinal nucleus
What are the functions of the three sensory nuclei?
Mesencephalic - proprioception
Main/principal - discriminative touch
Spinal nucleus - pain and temperature
In the event of an injury to the pars caudalis what would a more caudal injury result in?
Peripheral loss of pain and temp
Rostral = peripheral and central face
What is trigeminal neuralgia?
Brief episodes of extreme pain to area of CN V distribution (mostly mandibular)
How could surgery help trigeminal neuralgia?
Cutting nerve root, introducing lesion in trigeminal ganglion
Result: lose all tactile and pain to area
The most effective CN V neuralgia treatment would be to cut afferents just slightly caudal to obex, what would be the result and risk?
Result: keep tactile but lose pain over half of face
Risk: close to medullary cardiovascular and respiratory centers
