Flashcards in Bales: Head and Face Sensation-Trigeminal System Deck (15):
Where do the trigeminal nerve roots exit the brainstem?
at the upper lateral pons at its junction with the middle cerebellar peduncle
How many trigenimal sensory nuclei are there and where are they?
1. mesencephalic nucleus: located in dorsolateral midbrain adjacent to the periaqueductal gray
2. chief sensory nucleus: dorsolateral mid-to-rostral pons lateral to trigeminal motor nuc. Sandwiched between superior cerebellar peduncle and medial lemniscus
3. spinal trigeminal nucleus: located in uppermost spinal cord, dorsolateral medulla and most of pons (midpoint is ~ near the level of the obex)
the trigeminal nuclei span the brainstem
Which mesencephalic nucleus is unique to the CNS?
mesencephalic nucleus is a collection of primary sensory pseudo-unipolar neuron cell bodies (like a DRG)
*it is the only such nucleus within the CNS
Where do conscious proprioceptor neurons of the head and face project to? What else
the trigeminal chief sensory nucleus
the 1st order neurons for discriminative touch in the semilunar ganglion also project to the chief sensory nucleus
Where do most second order neurons for discriminative touch and conscious proprioception decussate? What tract do they join?
most 2nd order neurons decussate out of the chief sensory nucleus to joint the ventral trigeminothalamic tract (VTT).
These second order axons synapse in the ventral posteromedial (VPM) thalamic nucleus
Where will the 3rd order (VPM thalamocortical) fibers for touch and conscious proprioception go?
pass through the PLIC to the primary somatosensory cortex (BA 3,2,1. post central gyrus)
Where is the VTT located from the upper pons through the midbrain (rostral midbrain)? What would happen if there were a lesion to this area?
just dorsal to the medial lemniscus
if there were a lesion large enough to affect the medial lemniscus and the VTT, the pt would experience WHOLE body CONTRALATERAL hemisnesthesia (face and trunk and limbs)
How is the spinal trigeminal nucleus (STN) somatotopically organized?
concentrically (across V branch boundaries)
-central face represented more rostrally (pars oralis , around oral cavity)
-peripheral face represented more caudally (pars caudalis)
How is the STT somatotopically organized?
dorsoventrally around the trigeminal n. branches
CN 7, 9, and 10 course more dorsally, adjascet to mandibular
Would a spinal trigemninal tract (STT) lesion affect fibers at the level above or below?
STT lesions interrupt fibers at the level and BELOW--> sets an upper limit to the lesion
Where do 2nd order pain and temp neurons in the spinal trigeminal nuc. decussate?
at that level to course in the VTT
--> synapse in the VPM thalamus
Lesions to what 4 places would cause contralateral analgesia AND anesthesia of the head?
midbrain VTT, VPM thalamus, PLIC, or lower post central gyrus.
What would a lesion of the spinal trigeminal nucleus and tract produce?
ipsilateral analgesia (without loss of touch)
What are some similarities between sensory trigeminal and somatic sensory from the trunk and limbs?
1. 3 neuron chain from receptor to cortex
2. 2nd order neurons decussate
3. 3rd order neurons are in ventral posterior thalamic (lateral and medial)