0071509674.pdf

High-Yield Facts

Neural Pathways

ASCENDING PATHWAYS

Cells in the spinal cord receive inputs from ipsilateral structures. Pathways
to the thalamus cross to terminate on the contralateral side.
The major ascending pathways are the dorsal (posterior) columns and
the anterolateral system.

Pain,Temperature, and Tactile

• Simple receptors, unmyelinated, or poorly myelinated fibers.


• Enter via dorsal root and may ascend or descend a few segments.


• Secondary fibers cross the midline in the ventral commissure and ascend
  in ventral and lateral funiculi (ventral and lateral spinothalamic tracts).


• Terminate in ventral posterior lateral nucleus of thalamus.


• Tertiary fibers project via the internal capsule to terminate in the post-
  central gyrus.


• Injury to the spinothalamic tracts results in loss of pain and temperature
  sensation on the opposite side of the body.


• Syringomyelia interrupts pain and temperature fibers crossing in the
  ventral white commissure and thus results in bilateral sensory deficit.

Proprioception,Tactile Discrimination, and Stereognosis

• Primary fibers arising from more complicated receptors are generally
  well myelinated.


• Afferents enter the spinal cord via the dorsal root and ascend in the dor-
  sal funiculus. The dorsal funiculus divides into a medial fasciculus gra-
  cilis (sacral, lumbar, and lower thoracic inputs) and a lateral fasciculus
  cuneatus (upper thoracic and cervical inputs). Both fasciculi terminate in
  corresponding nuclei in the medulla.


• Secondary fibers from the nucleus gracilis and nucleus cuneatus cross
  the midline and ascend in the medial lemniscus to terminate in the ven-
  tral posterior lateral nucleus of the thalamus.


• Tertiary fibers terminate in the postcentral gyrus.


• Muscle spindle information is sent to the cerebellum via two major
  pathways. The dorsal spinocerebellar tract originates from Clarke’s

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