425
CHAPTER ELEVEN
Nervous System II
horn of the spinal cord. These neurons are found in all of the
thoracic segments and in the upper two lumbar segments of
the cord (T1–L2). Their axons exit through the ventral roots
of spinal nerves along with various somatic motor F
bers.
After traveling a short distance, preganglionic fibers
leave the spinal nerves through branches called
white rami
(sing.,
ramus
) and enter sympathetic ganglia. Two groups
of such ganglia, called
sympathetic chain ganglia
(paraver-
tebral ganglia) are located in chains along the sides of the
vertebral column. These ganglia, with the F
bers that connect
them, comprise the
sympathetic trunks
(f
g. 11.36)
.
The paravertebral ganglia lie just beneath the parietal
pleura in the thorax and beneath the parietal peritoneum in
the abdomen (see chapter 1, pp. 12 and 14). Although these
ganglia are some distance from the viscera they help con-
trol, other sympathetic ganglia are nearer to the viscera. The
collateral ganglia,
for example, are in the abdomen, closely
associated with certain large blood vessels
(f
g. 11.37)
.
Some of the preganglionic F
bers that enter paravertebral
ganglia synapse with neurons in these ganglia. Other F
bers
extend through the ganglia and pass up or down the sympa-
thetic trunk and synapse with neurons in ganglia at higher
or lower levels in the chain. Still other F
bers pass through to
Interneurons
Spinal cord
Dorsal root ganglion
Dorsal root
ganglion
Postganglionic
fiber
Preganglionic
fiber
Sensory
neuron
Autonomic
ganglion
Viscera
Skeletal
muscle
(b)
Somatic pathway
(a)
Autonomic pathway
Skin
Somatic motor neuron
Sensory
neuron
FIGURE 11.35
Motor pathways. (
a
) Autonomic pathways include two neurons between the CNS and an ef
ector. (
b
) Somatic pathways usually
have a single neuron between the CNS and an ef
ector. In both cases the motor F
bers pass through the ventral root o± the spinal cord.
Ventral root
Sympathetic
trunk
Paravertebral
sympathetic
ganglion
Spinal nerves
Transverse
process
Vertebral notch
(forms part of
intervertebral
foramen)
Spinal cord
Dorsal root
Dorsal root
ganglion
Pia mater
Arachnoid
mater
Dura
mater
Body of
vertebra
FIGURE 11.36
A chain o± paravertebral ganglia extends along each
side o± the vertebral column.
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