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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



through the marrow space are evident above the 

 genial tubercle, and multiple small foramina are 

 usually seen in the small triangular area on the inner 

 face of the ramus below the mandibular notch and 

 above or on the endocondylar and endocoronoid 

 ridges. 



Within the mandibular canal the inferior dental 

 artery gives rise to blood vessels which pass upward 

 toward the alveolar border (28). Some vessels pass 

 toward the lower border, but these are few in number. 

 The lower border of the mandible is supplied mainly 

 by periosteal vessels. The inferior dental artery within 

 the mandibular canal is surrounded by numerous 

 vessels, presumably venae comitantes. 



Some eleven areas of cortical bone are recognized 

 (36), the regions being based upon the direction of 

 the canals in the Haversian mesh. There is little evi- 

 dence of the presence of lacunae or canaliculi in the 

 adult. 



Nerve Supply of Bone 



Perhaps the most complete and careful study of the 

 innervation of bone has been carried out by Kuntz & 

 Richins (78). According to their study the absence of 

 any nerve fibers not in close proximity to blood 

 vessels, in preparations in which excision of the dorsal 

 root ganglia had resulted in degeneration of the af- 

 ferent fibers, leads to the conclusions: a) that the 

 parenchymatous tissue of the bone marrow is devoid 

 of direct afferent innervation, and />) that, in prep- 

 arations of normally innervated bone marrow, un- 

 myelinated fibers which exhibit no obvious relation- 

 ships to blood vessels represent unmyelinated afferent 

 fibers or the unmyelinated terminal portions of 

 myelinated ones. 



afferent fibers. The conception of some sensory 

 innervation of the bone marrow is supported by the 

 common clinical observation that puncture of bone 

 gives rise to pain, and the finding that many afferent 

 fibers in bone fall within the caliber range of the 

 pain-conducting fibers is in full agreement with this 

 view. Schleicher (100) noted that when blood plasma 

 was infused into the sternum a sharp pain was felt 

 about the infusion area when the pressure of the in- 

 coming fluid was greater than the intramedullary 

 pressure. In many persons with multiple myeloma 

 and metastatic bone lesions, distinct bone pain is asso- 

 ciated with sudden straining or coughing (94). It is 

 possible that the sudden elevation of intramedullary 

 pressure shown to result from such effort results in 



distortion of the arteries and arterioles bearing 

 sensory nerves and that this produces pain. 



When the sympathetic nerve fibers are caused to 

 degenerate by removing the appropriate sympathetic 

 ganglia, afferent fibers are found running to blood 

 vessels. They are present in relationships which indi- 

 cate that they are also connected with receptors im- 

 bedded in the parenchyma of the marrow (78). Foa 

 (47, 48) suggests that the afferent fibers may play a 

 part in the reflex regulation of functional activity of 

 bone marrow, and Chiray et al. (24) have shown that 

 the intramedullary injection of certain substances will 

 produce reflex changes in blood pressure. 



efferent fibers. The relation of the sympathetic 

 innervation to bone circulation has been studied 

 either by sectioning or stimulating sympathetic fibers. 

 It seems clear that cutting sympathetic fibers causes 

 vasodilation and hyperemia (39, 40, 48, 60), and that 

 stimulation produces vasoconstriction (39, 48, 60, 

 1 12). 



Hurrell (69) has traced nerve fibers into and along 

 Haversian canals of adult bone into two-thirds of the 

 thickness of the shaft of a cat's femur. Some end 

 blindly in the bone matrix; others, in close connection 

 with osteocytes. He suggests tentatively that the nerve 

 fibers found may be the two ends of a reflex arc 

 governing bone growth and maintenance. In this con- 

 nection Coppo (31) has reported a decrease in the 

 percentage of ash, and a modification of its composi- 

 tion, 8 to 1 5 davs after denervation of bone. Neverthe- 

 less, all experiments on animals have shown that uni- 

 lateral sympathectomy by itself has no observable 

 effect on bone growth (3, 21). The results obtained 

 from experiments on the effect of sympathectomy on 

 the healing of fractures are equivocal. Some investi- 

 gators have found healing to be accelerated (30), 

 whereas others have seen no effect (89). According to 

 Corbin & Hinsey (32), bones and joints are not sup- 

 plied with nerves having specific trophic functions. 



Blood Flow in Bone 



The circulation in bone is sufficient to supply the 

 normal variations of physiological processes, but often 

 fails to respond to the extreme insults of trauma or 

 infection. The delayed union of comminuted bumper 

 fracture of the tibia, and the extensive involvement of 

 the shaft of the long bones in osteomyelitis are classi- 

 cal examples. In situations where end arteries are 

 present, as at the metaphyseal side of the epiphyseal 

 plate, infarction is common. Aseptic infarction is 



