Human Anatomy Vol 1

THORAX

Ftg. A2.2: Actions of parasympathetic system

beginning of ventral rami via white ramus communicans
(wrc). There are 14 wrc on each side. These fibres can
have following alternative routes.
I They relay in the ganglion of the sympathetic trunks,
postganglionic fibres pass via the grey communicans
and get distributed to the blood vessels of muscles,
skin, sweat glands and to arrector pili muscles
(Fig. A2.3).
2 These may pass through the corresponding ganglion
and ascend to a ganglion higher before terminating
in the above manner.
3 These may pass through the corresponding ganglion
and descend to a ganglion lower and then terminate
in the above manner.

These may synapse in the corresponding ganglia and

pass medially to the viscera like heart, lungs,

oesophagus.

These white rami communicans (wrc) pass to cor-

responding ganglia and emerge from these as wrc

(unrelayed) in the form of splanchnic nerves to

supply abdominal and pelvic viscera after slmapsing

in the ganglia situated in the abdominal cavity. Some

fibres of splanchnic nerves pass express to adrenal

medulla.

Sympathetic trunk on either side of the body extends

from cervical region to the coccygeal region where both

trunks fuse to form a single ganglion impar. It has

cervical, thoracic, lumbar, sacral and coccygeal parts.

Thorocic Porl of Sympothetic lrunk

There are usually 11 ganglia on the sympathetic trunk

of thoracic part. The first ganglion lies on neck of Ist

rib and is usually fused with inferior cervical ganglion

and forms stellate ganglion. The lower ones lie on the

heads of the ribs. The sympathetic trunk continues with

its abdominal partby passingbehind the medial arcuate

ligament.

The ganglia are connected with the respective spinal

nerves via the white ramus communicans (from the

spinal nerve to the ganglion) and the grey ramus

communicans (from the ganglion to the spinal nerve,

i.e. ganglion gives grey).

Lateral grey horn

Ventral ramus

Dorsal ramus

Grey ramus

White ramus

Somatic afferent fibres

Splanchnic afferent fi bres

Sympathetic trunk

+

Preganglionic fibres

Fig. A2.3: Pathways of sympathetic and somatic nerves: Splanchnic afferent fibres and somatic afferent fibres (green); sympathetic

preganglionic efferent fibres (red); sympathetic postganglionic efferent fibres (red dotted); and somatic efferent fibres (black)