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).
Medical Definition of Sympathetic nervous system. Sympathetic nervous system: A part of the nervous system that serves to accelerate the heart rate, constrict blood vessels, and raise blood pressure. The sympathetic nervous system and the parasympathetic nervous system constitute the autonomic nervous system. Last Editorial Review: 5/13/2016.