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A TEXTBOOK OF PHYSIOLOGY 



Sensory impressions originating in the heart do not as a rule enter 

 into consciousness. Carried by the cardiac nerves to the sympathetic 

 ganglia, and thence to the upper thoracic region of the spinal cord, they 

 come into relation there with the sensory nerves from the pectoral region, 

 upper limb, shoulder, neck, and head. The impressions are not felt 

 in the heart, but referred to these sensory cutaneous nerves (Fig. 38' ). 

 Thus, cardiac pain is felt in the chest wall and upper limbs, and par- 

 ticularly on the left side. The function of the cardiac nerves is to- 



FIG. 84. AORTIC BLOOD-PKESSUKE. (L. H.) 



A, Effect of exciting the central end of vagus. The effect was depressor. B, On 

 shifting up the electrodes to a fresh unexposed part of the nerve the effect changed 

 to pressor. The time is marked in seconds. 



co-ordinate the beat of the heart with the needs of the body, and to 

 co-ordinate the functions of other organs with the needs of the heart. 

 For example, an undue rise of arterial pressure, induced, let us say, 

 by compression of the abdomen, excites the centre of the vagus, and 

 produces slowing of the heart and a consequent lowering of arterial 

 pressure. The heart of a mammal continues to functionate after a 

 section of all the branches of the cardiac plexus has been made, so 

 that the nervous control and co-ordination of the heart are not abso- 

 lutely essential to the continuance of life. 



