NETTER - Neuroscience Flash Cards

Somatosensory System: Dorsal Column
System and Epicritic Modalities
1. Cerebral cortex: postcentral gyrus
2. Posterior limb of the internal capsule
3. Ventral posterolateral (VPL) nucleus of the thalamus
4. Medial lemniscus
5. Nucleus gracilis
6. Nucleus cuneatus
7. Internal arcuate fibers
8. Fasciculus gracilis
9. Fasciculus cuneatus
10. Lateral cervical nucleus (C1 and C2 only)
11. Spinocervical tract
Comment: The dorsal column consists of the fasciculi gracilis
(T6 and below) and cuneatus (above T6) which convey epicritic
information fine discriminative touch, vibratory sensation, joint-position
sense, and secondary somatosensory modalities in myelinated axons
to nuclei gracilis and cuneatus. The secondary sensory axons of the
medial lemniscus are crossed (internal arcuate fibers) and terminate
in VPL nucleus of the thalamus. This nucleus projects to the primary
somatosensory cortex on the postcentral gyrus of the parietal lobe, as
well as to secondary somatosensory cortex. Thus, epicritic information
is interpreted in the contralateral hemisphere. Supplemental epicritic
information also is conveyed through the dorsal portion of the lateral
funiculus through the dorsal horn and the dorsal column nuclei. This
supplemental information accounts for the remaining presence of
some vibratory sensation and other epicritic information in patients
with extensive or even complete dorsal column lesions. Lesions in the
spinal cord may affect epicritic fibers or protopathic fibers selectively,
producing dissociated sensory loss of those modalities without
producing full anesthesia; selective lesions of the peripheral nerves
may also produce selective dissociated sensory loss by involving
small-diameter unmyelinated fibers (leprosy) or large-diameter
unmyelinated fibers (Guillain-Barré syndrome).
Systemic Neuroscience See book 14.4