Microneurography

Human microneurography or simply microneurography involves the insertion of metal microelectrodes into nerve fascicles.

Applications

Microneurography is used to study autonomic nervous system function. This is accomplished by recording muscle sympathetic nerve activity (MSNA). MSNA is a direct recording of sympathetic nerve activity representing postganglionic vasoconstrictor nerve traffic. Methodologically, this is done by using 200 µm diameter tungsten electrodes with a 2-5 µm uninsulated tip which are inserted into a postganglionic nerve fiber (commonly the peroneal or popliteal). This signal is then amplified, filtered (bandwidth 700-2,000 Hz), rectified and integrated to provide a mean voltage neurogram. This neurogram can be used to assess baroreflex sensitivity by the slope of the relationship of MSNA to diastolic blood pressure. A classic autonomic function test that uses microneurography to evaluate baroreflex sensitivity is a modified oxford test, in which two vasoactive drugs (sodium nitroprusside and phenylephrine) are given while beat to beat blood pressure and MSNA are recorded over 3 minutes.

Microneurography is also used to study and understand the neurophysiology of nerve fibers (both afferent and efferent) in the face and peripheral nervous system. Studies done in humans carry the advantage of communication, and have thus considerably helped in our understanding of receptive fields of mechanoreceptors.

Since recording is done in nerve fasicles the neuronal activity is directly related to the sensory afferents or motor efferents. That is to say, the firing rate of sensory afferents are directly from stimulation of receptors, whether in muscles, tendons, or skin. The same is true for efferent signals to skeletal muscle or smooth muscle. This is different than recording in the spinal cord or cortex where signals can be processed.

Health effects

Surprisingly microneurography appears to have little in the way of permanent detrimental effects to patients. Animal studies have shown that axonal damage does occur, but this axonal damage in animals does not translate into perceived damage or loss of function in human experiments. Symptoms such as abnormal sensations, deep muscle aches, muscle weakness, and loss of sensations are observed following the study, but generally not during the study. This observation has suggested that edema and not axonal damage is the cause of these symptoms. 95% of symptoms are resolved within 14 days.

References

S.C. Gandevia, J.P. Hales (1997). "The methodology and scope of human microneurography". Journal of Neuroscience Methods 74 (2): 123–136. doi:10.1016/S0165-0270(97)02243-7. PMID 9219882.