CONTROL OF PERIPHERAL CIRCULATION 
vasomotor innervation and it will not be possible to explore these 
areas adequately until a technique is devised which permits precise 
and quantitative measurement of skin blood flow over large tissue 
SUMMARY 
Recent experiments suggest that human skeletal muscle has both 
an adrenergic vasoconstrictor and a cholinergic vasodilator inner- 
vation. The former take part in certain baroreceptor and chemo- 
receptor reflexes, whereas the latter take part in the circulatory 
adaptations during emotional stress. Both sets of fibres can be 
activated independently of each other, and also independently of those 
supplying skin blood vessels. The chief vasomotor innervation of 
the extremities is vasoconstrictor. Here the vessels are normally 
subjected to a high degree of vasoconstrictor tone, and the reflex 
changes in blood flow which occur during temperature regulation can 
be explained by alterations in vasoconstrictor tone. The skin of the 
proximal parts of the limbs is not subjected to any appreciable 
vasoconstrictor or vasodilator tone when the subject is comfortably 
warm. However, during body cooling, the vessels constrict, due to 
vasoconstrictor fibre activity, and during body heating, they dilate, 
due to an active vasodilator mechanism mediated through fibres 
running with the cutaneous nerves. 
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