6 70 TEXT-BOOK OF PHYSIOLOGY 



bladder; (c) to augment the contraction of the detrusor muscle during urina- 

 tion; (d) to augment the tonus and contractile power of the muscle- walls of 

 the colon and rectum, and the rectal sphincters. 

 Summary. The autonomic system consists of: 



1. The autonomic tissues, viz.: the non-striated, visceral and vascular muscle 

 tissue, cardiac striated muscle tissue and epithelial tissue. 



2. The autonomic nerves. 



The autonomic nerves consist of two successively arranged neurons. 

 The first has its origin in cells of the central nerve system; the second has 

 its origin in cells of the sympathetic ganglia. The former is termed pre- 

 ganglionic, the latter post-ganglionic. The pre-ganglionic neuron arborizes 

 peripherally around the cells of the sympathetic ganglia; the post-ganglionic 

 terminates by fine branchings around the cells of the tissues. 



The pre-ganglionic neurons have their origin in four separate regions of 

 the central nerve system, viz.: (i) The mid-brain region; (2) the medulla 

 oblongata; (3) the mid-spinal cord region and (4) the sacral region. 



The autonomic system of nerves as evident from their distribution com- 

 prises : 



1. The viscero-augmentor and viscera-inhibitor nerves for the non-striated 



muscles of the eyeball (iris and ciliary muscle) of the lower portion of 

 the esophagus, of the trachea and bronchial tubes, of the stomach, of 

 the small and large intestine, the gall-bladder and the pelvic organs. 



2. The vaso-dilatator nerves for the non-striated muscles of the blood-vessels 



of the salivary glands, the mucous and serous glands of the nose, mouth 

 and pharynx, and of the genital organs. 



3. The vaso-constrictor nerves for the non-striated muscles of the blood-ves- 



sels of the skin of the head, face, neck, trunk, arms, and legs, alimentary 

 canal, liver, spleen, kidney, adrenals and genital organs. 



4. The cardio-augmentor and cardio-inhibitor nerves for the heart. 



5. The secreto-augmentor and secreto-irihibitor nerves for the epithelial tissue 



of the salivary glands, of the mucous and serous glands of the mouth, 

 nose, and pharynx, of the trachea and bronchial tubes, of the gastric 

 glands, of the thyroid, of the pancreas, of the adrenals, of the liver, and 

 the sweat-glands of the skin of the head, face, neck, trunk, arms, legs 

 and of the glands in connection with the genital organs. 

 The centers of origin of the autonomic nerves possess a certain degree of 

 tonus, maintained in all probability by changes of a chemic character, be- 

 tween the constituents of the nerve cells and the constituents of the blood by 

 which they are surrounded. In consequence of this tonus, they maintain a 

 certain degree of activity in the tissues to which the autonomic fibers are dis- 

 tributed. Given this tonus the autonomic centers may be excited to in- 

 creased activity: (i) By nerve impulses transmitted by afferent nerves from 

 the surfaces of the body; and (2) by nerve impulses descending from the 

 cerebrum in consequence of psychic states of an affective or emotional 

 character. 



The nature and strength of the stimulus applied to the surface of the 

 body, and the nature and intensity of the affective or emotional state will 

 naturally determine the degree and extent of the resulting activity of the 

 autonomic tissues. 



