PNB 2XB3 Lecture 4: Somatosensory System Exam Study Guide with Complete Solutions
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Course
PNB 2XB3
Institution
PNB 2XB3
PNB 2XB3 Lecture 4: Somatosensory
System Exam Study Guide with
Complete Solutions
dermatome - Answer-the area of skin supplied by the sensory axons of a single
spinal nerve
dorsal horn - Answer-the POSTERIOR column of grey matter in the spinal cord
(shape differs depending on spinal segment) ...
C axon - sensory function - Answer✔✔-pain, temperature, and itch (thermoceptive
and nociceptive)
C axon -receptor type - Answer✔✔-free nerve endings (unmyelinated)
C axon - axon diameter - Answer✔✔-0.2-1.5 microns
C axon - conduction velocity - Answer✔✔-0.5-2 m/s
dorsal root ganglion (DRG) - Answer✔✔-(part of the PNS) cluster of cell bodies in the
dorsal root of a spinal nerve (when the action potential reaches the DRG, it splits into 2 -
one travels toward the cell body and the other continues down the axon)
variation in conduction velocity exists because - Answer✔✔-there is variation in
myelination and axon diameter (speed: Aβ > Aδ > C)
why are there TWO pain sensations? - Answer✔✔-1) first sharp pain sensation
arrives fastest via Aδ axon
2) second duller pain sensation is delayed because it travels at a slower speed via C
axon
dorsal column medial lemniscus (DCML) pathway - Answer✔✔-- decussates in the
medulla
- synapses in the dorsal column nuclei, thalamus (VPL nucleus), and somatosensory
cortex
spinothalamic (anterolateral) tract (STT) - Answer✔✔-- decussates in the dorsal horn
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