1526 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



dorsal ganglia. They are largely unmyelinated in their 

 myocardial course (153, 397), and supply the pain- 

 sensitive areas in the pericardium, connective tissue, 

 adventitia, and walls of the heart, terminating as fine 

 beaded nerve fibers and loops similar to those in the 

 skin and skeletal muscle. Sensory axons traveling in 

 sympathetic plexuses and through the lower two 

 cervical and upper four thoracic sympathetic ganglia 

 complete the afferent limb of the pain reflex. In both 

 man and dog, ablation of the stellate and upper four 

 thoracic ganglia, or upper four dorsal thoracic spinal 

 roots, completely blocks the pain pathway (397 ). 

 These neurons send fibers via the posterior spinal 

 roots which synapse in the posterior spinal horn with 

 secondary fibers running in the spinothalamic tracts 

 and terminating in the posterior-ventral nucleus of 

 the thalamus (fig. 5). While connections to the cortical 

 somatic sensory areas exist, these only modify the 

 reaction to, rather than the perception of, cardiac 

 pain. 



The autonomic innervation includes both an af- 



ferent and efferent vagal and sympathetic supply. 

 Vagal parasympathetics are mediated by the cardiac 

 plexus and stem from both right and left vagi and the 

 recurrent laryngeal nerves. A large portion of both 

 afferent and efferent fibers is distributed to the great 

 vessels superior to the heart, while the greatest part of 

 the remainder supply the interatrial septum and the 

 sino-atrial and A-V nodal areas (12, 76, 153, 368, 

 397). The large number of fibers in the latter areas 

 contrasts with the paucity of fibers supplied to the 

 atrial muscles via atrial arteries and the even smaller 

 number found in the ventricles. Using veratrum alka- 

 loids, only the left coronary artery system, i.e., the left 

 ventricle, has been found to contain afferent vagal 

 ganglia which contribute to the Bezold-Jarisch reflex 

 while, conversely, no efferent vagal supply is present 

 in either ventricle (12, 76, 368). The sympathetic 

 efferent discharge is largely to ventricular muscle and 

 coronary arteries and contains both cardiomotor 

 and vasomotor fibers, while atrial efferents are pre- 

 dominantly to the S-A node and are cardio-accelera- 



SUP 



CERVICAL GANGLION!^ 



MIDDLE 



CERVICAL GANGLIONJ 



UPPER SENSORY 

 NEURON IN 

 SPINOTHALAMIC 

 TRACT 



LEG 



PARAVERTEBRAL CHAIN OF 

 SYMPATHETIC GANGLIA 



DIRECT THORACIC 

 CARDIAC NS. 



OCCASIONAL CONNECTING 

 RAMUS TO 



SPINOTHALAMIC TRACT 



fig. 5. Illustration of the cardiac nerves and their central communications. Parasympathetic ef- 

 ferent and afferent fibers from the vagus and recurrent nerves join the cardiac plexuses at the base of the 

 heart. [From White (397).] 



