CHAPTER XIII 

 NERVOUS CONTROL OF THE CIRCULATION 



240. Functions of the Nerves of the Circulatory System. 

 When any special activity is required of one of the organs 

 of the body, an increased flow of blood is needful to that 

 part. There is not blood enough in the body to enable 

 all the muscles, all the organs of digestion, the brain, and 

 the organs of respiration, etc., to work in full activity at 

 the same time. There must therefore be some method of 

 regulating the activities of the different parts and organs, 

 so that some may rest while others work. 



Then, too, some arrangement must exist for correlating 

 the action of the heart and the blood vessels, so that the 

 steady flow of nourishing blood may be kept up in all the 

 capillaries, with more powerful pressure applied when and 

 where it is needed, and not at the wrong place and the 

 wrong time. 



As everywhere else, we find that in the circulatory 

 system the nerves furnish the controlling, coordinating, 

 and regulating force. 



241. Nerves of the Heart (Fig. 99). Three sources of 

 nervous control of the heart are usually mentioned. They 

 are the cardiac or heart branches of the tenth and eleventh 

 pairs of cranial nerves, the vagus or pneumoyastric and 

 the spinal accessory; the cardiac branches of the sympa- 

 thetic^ from the ganglia of the neck ; and what have 



