98 Neuroanatomy: Draw It to Know It
Sympathetic Nervous System
Here, we will draw the motor division of the thora-
columbar sympathetic nervous system. Across the top of
the page, write nucleus, ganglion, and eff ector tissue.
Next, draw an outline of the spinal cord; show that the
origins of the sympathetic nervous system lie in the
intermediolateral cell column from T1 to L2. Now,
draw the paravertebral chain; it resembles a string of
pearls and lies just lateral to the vertebral column: we
draw it as four circles and a long tail because only 4 of
the roughly 24 sympathetic ganglia are worth specifying
for our purposes, here. Label them now from superior to
inferior as the superior cervical ganglion, the middle cer-
vical ganglion, the inferior cervical ganglion, and, lastly,
the fi rst thoracic ganglion. Th e inferior cervical and fi rst
thoracic ganglia combine to form the stellate ganglion.
Next, show that there are 10 additional thoracic para-
vertebral ganglia (for a total of 11), and 4 lumbar para-
vertebral ganglia, and 4 or 5 sacral paravertebral ganglia,
and the ganglion impar, the most caudal paravertebral
ganglion, which neighbors the coccyx.^9
Now, let’s divide the sympathetic motor innerva-
tion into its diff erent anatomic segments. First, draw
the innervation to the thorax and upper abdomen:
show that preganglionic sympathetic fi bers synapse in
the paravertebral chain and then project the long dis-
tance to their thoracoabdominal targets. Th e targets
within this anatomic segment include the lungs, trachea,
heart, and esophagus; the preganglionic sympathetic
fi bers that innervate this segment originate in the inter-
mediolateral cell column from T1 to T5.
Next, let’s show the innervation pattern to the upper
extremity. Indicate that it stems from postganglionic
fi bers of the middle cervical and stellate paravertebral
ganglia. Th en, also show that the stellate ganglion plays
an important supplementary role in sympathetic inner-
vation to the heart.
Now, in regards to the head and neck, show that the
superior cervical ganglion receives innervation from
the C8 to T2 spinal cord level: this region is called
the cilisopinal center of Budge; and then, show that the
cilisopinal center of Budge is innervated by the postero-
lateral hypothalamus via the hypothalamospinal path-
way. Next, show that postganglionic superior cervical
ganglion fi bers ascend the carotid arteries to innervate
the head and neck. Notable causes of injury along this
sympathetic pathway are medullary brainstem strokes,
paravertebral masses, such as Pancoast tumor (a form of
apical lung tumor), and carotid dissection. Loss of sym-
pathetic tone to the face results in Horner’s syndrome:
ptosis, miosis, and anhidrosis.
Next, we will draw the innervation to the rest of the
abdomen and pelvis, which is derived from sympathetic
splanchnic nerves, which generally originate from the
T5 to L2 level of the spinal cord. Rather than relay in the
paravertebral ganglia, show that these nerves, instead,
synapse in the four prevertebral ganglia, which span
from the lower thoracic to the sacral vertebral column.
Indicate that the prevertebral ganglia are, from superior
to inferior: the celiac, aorticorenal, superior mesenteric,
and inferior mesenteric ganglia. Th en, show that the
celiac ganglion innervates the spleen and foregut deriva-
tives; the aorticorenal ganglion innervates the renal ves-
sels; the superior mesenteric ganglion innervates the
midgut derivatives; and the inferior mesenteric ganglion
innervates the hindgut derivatives, the lower urinary
system, and the reproductive organs.^5
As our last anatomic segment, show that pregangli-
onic sympathetic fi bers synapse directly in the adrenal
gland, most commonly on adrenal medullary chromaffi n
cells, which predominantly release epinephrine (and to a
much lesser extent norepinephrine).^1
Finally, within the sympathetic nervous system, we
need to show that both divergence and convergence of
preganglionic sympathetic fi bers occurs. Indicate that in
divergence, fi bers from one preganglionic axon form
synapses on multiple postganglionic neurons, whereas in
convergence, there is a confl uence of fi bers from diff er-
ent preganglionic axons onto a single postganglionic
neuron.^4 – 8 , 10