Stimulating and recording from axons within their myelin sheaths: a stable and nondamaging method for studying single motor units.

The contractile properties and activity patterns of single thyroarytenoid motor units were determined by stimulating and recording from their motoneuron axons within the recurrent laryngeal nerve. Most micropipette penetrations were within the myelin sheaths of axons but were functionally similar to actual axon impalements with respect to activation and recording of action potentials. Sheath penetrations were, however, less damaging to axons and were preferred for that reason. A myelin sheath approach combined the advantages of commonly used extra-axonal and intracellular methods for studying motor unit properties without their disadvantages. Specifically, the technique was stable, noninjurious in nature, and ensured stimulation and recording from the same motoneuron.