502
UNIT 3
Regulation and Integration of the Body
13
Dorsal root
ganglion
Gray matter
White matter
Ventral root
Dorsal root
Dorsal and ventral
rootlets of spinal
nerve
Dorsal ramus
of spinal nerve
Ventral ramus
of spinal nerve
Sympathetic trunk
ganglion
Spinal nerve
Rami communicantes
(a) Anterior view showing spinal cord, associated nerves, and vertebrae. The dorsal
and ventral roots arise medially as rootlets and join laterally to form the spinal nerve.
Dorsal ramus
Ventral ramus
Intercostal nerve
Spinal nerve
Rami communicantes
Dorsal root ganglion
Dorsal root
Ventral root
Sympathetic trunk
ganglion
Sternum
(b) Cross section of thorax showing the main roots and branches of a spinal nerve.
Branches of intercostal nerve
Lateral cutaneous
Anterior cutaneous
Figure 13.8
Formation of spinal
nerves and rami distribution.
Notice
the dorsal and ventral roots and rami.
In the thorax, each ventral ramus
continues as an intercostal nerve.
(The small meningeal branch is not
illustrated.)
intervertebral foramina. Because motor and sensory fibers min-
gle in a spinal nerve, it contains both efferent and afferent fibers.
Te spinal roots become progressively longer from the supe-
rior to the inferior aspect of the cord. In the cervical region, the
roots are short and run horizontally, but the roots of the lumbar
and sacral nerves extend inferiorly for some distance through
the lower vertebral canal as the
cauda equina
before exiting the
vertebral column (Figure 13.7).
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