Page 413 - Clinical Anatomy

ECA6 7/18/06 6:54 PM Page 398

398 The central nervous system

2◊◊To ascend or descend in the sympathetic chain with relay in higher or
lower ganglia.
3◊◊To traverse the ganglia intact and relay in peripheral ganglia.
Pharmacologically, the sympathetic postganglionic terminals release
adrenaline and noradrenaline, with a single exception of the sweat glands,
which, in common with all the parasympathetic postganglionic termina-
tions, release acetylcholine.

Distribution
The branches of the sympathetic ganglionic chain have somatic and vis-
ceral distribution.

Somatic distribution

Each spinal nerve receives one or more grey rami from a sympathetic gan-
glion which distributes postganglionic non-medullated sympathetic fibres
to the segmental skin area supplied by the spinal nerve. These fibres are
vasoconstrictor to the skin arterioles, sudomotor to sweat glands and pilo-
motor to the cutaneous hairs.

Visceral distribution

Postganglionic fibres to the head and neck and to the thoracic viscera arise
from the ganglion cells of the sympathetic chain. Those to the head ascend
along the internal carotid and vertebral arteries, whereas those to the thoracic
organs are distributed by the cardiac, pulmonary and oesophageal plexuses.
The abdominal and pelvic viscera, however, are supplied by postgan-
glionic fibres which have their cell stations in more peripherally placed
prevertebral ganglia—the coeliac, hypogastric and pelvic plexuses—which
receive their preganglionic fibres from the splanchnic nerves (Fig. 277).
These nerves are detailed on page 49.
The suprarenal medulla has a unique nerve supply comprising a rich
plexus of preganglionic fibres which pass without relay from the coeliac
ganglion to the gland. These fibres end in direct contact with the chromaffin
medullary cells, and liberate acetylcholine (as in all autonomic ganglia)
which stimulates the secretion of adrenaline and noradrenaline by the
suprarenal medulla.
The chromaffin cells of the suprarenal medulla may thus be regarded as
sympathetic cells which have not developed postganglionic fibres; indeed,
embryologically both the medulla and the sympathetic nerves have a
common origin from the neural crest.

Clinical features

Cervical sympathectomy—see page 309.
Lumbar sympathectomy—see page 154.