136 Neuroanatomy: Draw It to Know It
Nerve Roots & Rami
To draw the anatomy of the nerve roots and rami, fi rst
draw an outline of an axial cross-section through the
spinal cord. Th en, draw the spinal cord dorsal and ven-
tral gray matter horns. Next, draw the anterior-lying ver-
tebral body. Th en, draw the pedicle on the right side of
the page but leave out the pedicle on the left ; otherwise
we would obstruct our view of the dorsal root ganglion,
which sits in the intervertebral foramen, underneath the
pedicle. Next, draw the transverse processes, then the
laminae, and fi nally the spinous process. We leave out
the articular processes, which form facet joints between
the vertebral arches.
Now, draw an anterior horn cell on the right side of
the spinal cord (the left side of the page) and show a ven-
tral root emerge from it. Th e ventral root carries motor
fi bers. Next, show a dorsal root enter the dorsal horn: it
carries sensory fi bers. As mentioned, underlying the pedi-
cle is the intervertebral foramen. Within the interverte-
bral foramen, attach a dorsal root ganglion to the posterior
nerve root. Th e dorsal root ganglion houses the cell
bodies of sensory nerves. Sensory cell bodies are pseudo-
unipolar because they contain a short axon with bipolar
processes that pass both centrally and peripherally. Next,
just distal to the dorsal root ganglion, indicate that the
anterior and posterior roots join to form a mixed spinal
nerve, which then separates into dorsal and ventral rami.
In brief, dorsal rami innervate the paraspinal muscles
and provide sensory coverage to the back of the head and
posterior trunk, whereas the ventral rami provide motor
and sensory innervation to a far more widespread group
of muscles and sensory areas, including the anterior
trunk and upper and lower limbs.
Show a representative thoracic nerve originate from
the anterior ramus and pass along the chest wall to form
an intercostal nerve. Now, turn your attention back to
where the rami split to draw the sympathetic ganglion
and related autonomic rami. Along the ventral ramus,
attach the white ramus, so named because it is myeli-
nated. Th en, more proximally, just past the takeoff of the
dorsal ramus, attach the gray ramus, which is unmyeli-
nated. Indicate that the gray and white rami meet in a
paravertebral sympathetic ganglion. Sympathetic ganglia
form two long chains that fl ank the vertebral column;
the sympathetic cell bodies lie within the intermediolat-
eral cell column of the spinal cord and project to the
paravertebral sympathetic chains.
Finally, show an impulse travel along the ventral
ramus and then up the white ramus to the paravertebral
sympathetic ganglion. Th en, show it pass down the gray
ramus back to the ventral ramus. From there, the impulse
disseminates along either the dorsal ramus or the ventral
ramus.^2 , 4 , 7 , 17