At any moment, each of these specialized brain neurons might be receiving multiple messages from multiple sources, but is only selectively responding to certain information about the timing or frequency of the impulses it is receiving. Related Stories.
Methods for measuring sympathetic nervous system activity. Heart rate variability (HRV), the beat-to-beat variation in heart rate, is an indirect method of measuring autonomic nervous system activity, with contributions from both the sympathetic and parasympathetic nervous systems.ine electrodes are used to record 'bursts' of activity from multiple or single afferent and efferent nerve axons in the skin and muscle. The common peroneal nerve is typically chosen for this method (because it is easily accessible) and measures the efferent postganglionic muscle sympathetic nerve activity (MSNA).
The blood vessels of skeletal muscles, in contrast, has beta 2 receptors which causes vasodilation. Hence sympathetic stimulation cause vasoconstriction of blood vessels of viscera and dilates the vessels of skeletal muscles redirecting blood flow to skeletal system, thus preparing for fight, flight, fright reaction.The heart rate also increases, forcing more blood to flow to muscles.Hope this helps :).ut at the same time they cause vasoconstriction of arteries carrying blood to the digestive organs, kidneys, and all those other internal organs that are not necessary for short-term survival (which is what the sympathetic system is all about).