Page 412 - Clinical Anatomy

ECA6 7/18/06 6:54 PM Page 397

The autonomic nervous system 397

descends in a groove between psoas major and the sides of the lumbar verte-
bral bodies, overlapped by the abdominal aorta on the left and the inferior
vena cava on the right. The chain then passes behind the common iliac
vessels to enter the pelvis anterior to the ala of the sacrum and then descends
medial to the anterior sacral foramina. The sympathetic trunks end below by
meeting each other at the ganglion imparon the anterior face of the coccyx.
The details of the cervical, thoracic and lumbar portions of the trunk are
given on pages 331, 47 and 153 respectively.
The sympathetic trunk bears a series of ganglia along its course which
contain motor cells with which preganglionic medullated fibres enter into
synapse and from which non-medullated postganglionic axons originate.
Developmentally, there was originally one ganglion for each peripheral
nerve, but by a process of fusion these have been reduced in man to three cer-
vical, twelve or less thoracic, two to four lumbar and four sacral ganglia.
Only the ganglia of T1 to L2 receive white rami directly; the higher and lower
ganglia must receive their preganglionic supply from medullated nerves
which travel through their corresponding ganglia without relay and which
then ascend or descend in the sympathetic chain. Still other preganglionic
fibres pass intact through the ganglia to peripheral visceral ganglia for relay.
There are thus three fates which may befall white rami (Fig. 276).
1◊◊To enter into synapse from the corresponding sympathetic ganglion
(this applies only to the T1 to L2 segments).

Fig. 276◊The three fates
of sympathetic white
rami. These may (A)
relay in their
corresponding ganglion
and pass to their
corresponding spinal
nerve for distribution, (B)
ascend or descend in the
sympathetic chain and
relay in higher or lower
ganglia, or (C) pass
without synapse to a
peripheral ganglion for
relay.