Autonomic Control of Blood Flow

When the sympathetic nervous system is activated, blood flow to the abdominal organs is decreased, while blood flow to the muscles is increased. For a long time, scientists believed that there must be sympathetic nerve endings on blood vessels in the muscles which increased the blood flow. This belief persisted in the absence of any evidence that such nerve endings actually existed.

More recent evidence indicates that the autonomic control of blood flow is mediated by the gaseous neurotransmitter nitric oxide (NO). The response is neither purely adrenergic nor cholinergic; rather a mixture of different autonomic effects appears to increase NO release, which in turn dilates blood vessels locally and also open up the precapillary sphincters which regulate blood flow to the capillary beds.