Point
4
Intro
Point: 4. Nucleus Gracilis-Cuneatus-Medial Lemniscus
Function:
Discriminative touch, conscious proprioception, and
vibration sense from the leg, trunk, and arm.
Pathway:
Central processes of dorsal root neurons T7 and below ascend
in IPSI. fasciculus gracilis to reach nucleus gracilis in
the caudal medulla. Processes of dorsal root ganglion cells
T6 and above ascend in IPSI. fasciculus cuneatus and end in
nucleus cuneatus. Axons from cells in nucleus gracilis and
cuneatus pass ventrally as internal arcuate fibers, cross
the midline and form the medial lemniscus. Medial lemniscus
ascends to V.P.L. Cells in V.P.L. project to somatosensory
cortex.
Deficits:
Lesion in fasciculus gracilis, nucleus gracilis, fasciculus
cuneatus and nucleus cuneatus results in IPSI. deficits in 2
point discrimination, vibration sense, and conscious
proprioception from the leg and arm respectively. Lesion in
the medial lemniscus results in CONTRA. deficits.
Other Note:
Lesion in internal arcuate fibers before they cross the
midline results in IPSI. deficits. Lesion of crossing fibers
from both sides=bilateral loss.