Human Anatomy Vol 1

INTRODUCTION

Appendix 2 at the end of the section on thorax gives a
bird's eye view of the sympathetic component of the
autonomic nervous system. The course of the typical
and atypical intercostal nerves is described briefly.
Arteries of thorax have been tabulated in Tables A2.2
and A2.3. Clinical terms are also given.

AUIONOMIC NER US SYSIEM

The autonomic nervous system comprises sympathetic
and parasympathetic components. Sympathetic is
active during fright, flight or fight. During any of these
activities, the pupils dilate, skin gets pale, blood
pressure rises, blood vessels of skeletal muscles, heart,
and brain dilate. There is hardly any activity in the
digestive tracts due to which the individual does not
feel hungry. The person is tense and gets tired soon
(Fig. 42.1).
Parasympathetic has the opposite effects of
sympathetic. This component is sympathetic to the
digestive tract. In its activity digestion and metabolism

a

I

-Murphy's low

of food occurs. Heart beats normally. Person is relaxed

and can do creative work (Fig. A2.2).

Autonomic nervous system is controlled by brain

stem and cerebral hemispheres. These include reticular

formation of brainstem, thalamic and hypothalamic

nuclei, limbic lobe and prefrontal cortex including the

ascending and descending tracts interconnecting these

regions.

Sympothetic Nervous Syslem

Sympathetic nervous system is. the larger of the two

components of autonomic nervous system. It consists

of two ganglionated trunks, their branches, prevertebral

ganglia, plexuses. It supplies all the viscera of thorax,

abdomen and pelvis, including the blood vessels of

head and neck, brain, limbs, skin and the sweat glands

as well as arrector pilorum muscle of skin of the whole

body.

The preganglionic fibres are the axons of neurons

situated in the lateral horns ofT1,-L2 segments of spinal

cord. They leave spinal cord through their respective

ventral roots, to pass in their nerve trunks, and

Fig. A2.1: Actions of sympathetic system