NERVOUS SYSTEM f^^^ 



next fibre ; in somatic nerves this is acetylcholine, but, as described 

 below, there are differences in the autonomic system. 



The visceral motor system, excluding that part of it wliich 

 innervates the branchial and other voluntary musculature, has 

 some pecuharities of structure and behaviour, and is known as 

 the autonomic system. Its fibres differ from those of the ordinary 

 peripheral nerves, in that a single one does not reach directly 



fefenc. 



dicnc. 

 mesenc. 



metenc. 



myelenc. 



sympathetic 

 ch&in 



eye 



H9ad: 



sa/ivary g lands 

 sweat glands 



Upper limb: 

 b. vessels 

 sweat glands 



heart 



bronchi 



lungs 



stomach 

 liver 



pancreas 

 Ifidnsy 

 intestine 

 colon 



colon 

 ■r bladder 

 reproductive 

 organs 



Sacra/ 



pelvic 

 ganglion 



Fig. 472. — Diagram of the autonomic nervous system of higher vertebrates. — 



From Thomson. 



The sympathetic system is indicated by unbroken hnes, the parasympathetic by broken lines. Where 

 ganglia are shown solid black a sympathetic path is continuous, in the others the pre- and post- 

 ganglionic nerves are in association through synapses or relays. 



to the organ which it is going to affect. Sooner or later each fibre 

 from the central nervous system comes to a s\'napse, and its 

 impulse is relayed to another neuron. The bodies of these secon- 

 dary neurons are collected into special ganglia, many of wliich 

 are a long way from the central nervous system. The post- 

 ganglionic fibres (the axons of the second neurons) are usuall\ 

 non-meduUated, and make up the autonomic nerves in the 

 limited sense ; the preganglionic fibres are the axons of the 

 connector neurons, running from the central nervous system to 

 autonomic ganglia. 



