Posterior Column-Medial Lemniscus pathway (PCML) & Trigem. Nuclei Flashcards
What does the PCML pathway transmit?
Somatosensory - touch (texture, size, shape), tactile information and proprioception
What is proprioception?
Knowing where your body is in space without seeing
Primary afferent fibers
Sensory fibers
Where do primary afferent fibers enter the spinal cord?
Medial division of posterior root
What do the afferent fibers ascend as?
Posterior column
Posterior column - grey or white matter?
White
Afferent fibers from sacral level - T6 go where in the posterior column?
Fasciculus Gracilis
Afferent fibers from T6 - superior go where in the posterior column?
Fasciculus cuneatus
Where is the fasciculus gracilis?
Medial side of posterior column
Where is the fasciculus cuneatus?
Lateral side of posterior column
Afferent fibers from ex. T9 will go to what side of the posterior column?
Medial
Afferent fibers from ex. T3 will go to what side of the posterior column?
Lateral
What will lesions in the posterior column produce?
IPSILATERAL sensation loss at and below affected segment
What is sensory ataxia?
Loss of reflexes and proprioception from extremities due to lack of sensory input
How may a patient with sensory ataxia stand?
With a wide base to try and reestablish the proprioception
If the fibers run in the fasciculus gracilis, where will they synapse?
Gracile nucleus
If the fibers run in the fasciculus cuneatus, where will they synapse?
Cuneate nucleus
2nd order neurons from either cuneate or gracile nucleus project where?
Contralateral thalamus
Where are the cuneate and gracile nuclei located?
Posterior Medulla
Once the fibers synapse at either the cuneate/gracile nuclei, then what happens?
They cross the midline and become the medial lemniscus
Sensory decussation
Crossing midline
How do fibers cross the midline at the posterior medulla?
Internal arcuate fibers
Where do the 2nd order neurons synapse?
Contralateral thalamus - VPL
Where do 3rd order neurons from the VPL project?
Primary Somatosensory cortex
What is the blood supply to the VPL?
Posterior cerebral A.
If the posterior cerebral A. is occluded, what will be affected?
Contralateral sensation of the body
What is included in the primary somatosensory cortex (S1)?
Postcentral gyrus and posterior paracentral gyrus
What body parts map to the posterior paracentral gyrus?
Foot, LE, hip
What artery supplies the posterior paracentral gyrus?
Anterior cerebral A.
If the anterior cerebral A. is occluded, what is affected?
Contralateral LE sensation
What body parts map to the postcentral gyrus?
Chest, UE, face, throat
What artery supplies the postcentral gyrus?
Middle cerebral A.
If the middle cerebral A. is occluded, what is affected?
Contralateral chest, UE, face, throat sensation
What inputs does the secondary somatosensory cortex receive?
Ipsilateral primary somatosensory cortex and VPI or thalamus
If the parietal cortical regions have lesions, what occurs?
Agnosia - contralateral side
What is agnosia?
Limb not recognized as part of patients own body but sensation is not super affected
What are the 4 trigeminal nuclei?
Mesencephalic, principal sensory nucleus, spinal nucleus and trigeminal motor nucleus
What afferent signals does the mesencephalic nucleus transmit?
Proprioception from TMJ, muscles of mastication and extraocular muscles
What does the principal sensory nucleus transmit?
Touch and pressure
Describe the orientation of the principal sensory nucleus
Face is oriented upside down - anteriorly = V1 and posteriorly = V3
Anterior trigeminothalamic tracts project to which VPM of thalamus?
Contralateral
Posterior trigeminothalamic tracts project to which VPM of thalamus?
Ipsilateral
Which nucleus is the only one that has pseudopolar neurons?
Mesencephalic
Describe the jaw jerk reflex
Stretch massater muscle down, axon synapses at trigeminal motor nuclues, and then both massaters contract
– testing trigeminal motor nucleus and V3
