Group C Nerve Fiber - Microneurography

Microneurography

Microneurography is a technique using metal electrodes to observe neural traffic of both myelinated and unmyelinated axons in efferent and afferent neurons of the skin and muscle. This technique is particularly important in research involving C fibers. Single action potentials from unmyelinated axons can be observed. Recordings from efferent postganglionic sympathetic C fibers of the muscles and skin yield important insights into the neural control autonomic effector organs like blood vessels and sweat glands. Readings of afferent discharges from C nociceptors identified by marking method have also proved as important tools to revealing the mechanisms underlying sensations such as itch.

Unfortunately, interpretation of the microneurographic readings can be difficult because axonal membrane potential can not be determined from this method. A supplemental method used to better understand these readings involves examining recordings of post-spike excitability and shifts in latency; these features are associated with changes in membrane potential of unmyelinated axons like C fibers. Moalem-Taylor et al. experimentally used chemical modulators with known effects on membrane potential to study the post-spike super-excitability of C fibers. The researchers found three resulting events. Chemical medulators can produce a combination of loss of super-excitability along with increased axonal excitability, indicating membrane depolarization. Secondly, membrane hyperpolarization can result from a blockade of axonal hyperpolarization-activated current. Lastly, a non-specific increase in surface charge and a change in the voltage-dependent activation of sodium channels results from the application of calcium.