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Updated: Jun 27, 2026
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In Vivo Electrophysiological Measurement of the Rat Ulnar Nerve with Axonal Excitability Testing
Published on: February 6, 2018
Axonal excitability in the forearm: normal data and differences along the median nerve
1Institute of Clinical Neurosciences, Royal Prince Alfred Hospital and University of Sydney, Medical Foundation Building K-25, Sydney, NSW 2006, Australia. s.jankelowitz@med.usyd.edu.au
Summary
Axonal excitability differs along the human median nerve, even at a single stimulation site. Normal values for one muscle group, like flexor carpi radialis (FCR), cannot be assumed for another, such as abductor policis brevis (APB).
Area of Science:
- Neuroscience
- Clinical Electrophysiology
Background:
- Axonal excitability studies are crucial for understanding nerve function and diagnosing disorders.
- Previous studies have primarily focused on specific nerve segments or muscle groups, potentially overlooking regional variations.
Purpose of the Study:
- To validate excitability studies of motor axons in the median nerve at the elbow, specifically targeting forearm muscles (flexor carpi radialis, FCR).
- To establish normal data for this stimulation site and assess differences in excitability measures based on stimulation site and tested muscle group.
Main Methods:
- Median nerve stimulation at the elbow, with excitability recorded from FCR and abductor policis brevis (APB) muscles.
- Median nerve stimulation at the wrist, with recordings from APB.
- Utilized the TRONDCM protocol with QTRACS for all excitability studies.
Main Results:
- Stimulus-response curves for FCR axons were significantly less steep compared to APB axons.
- FCR axons exhibited "fanning in" of threshold electrotonus and reduced accommodation to hyperpolarizing pulses.
- FCR studies demonstrated significantly less supernormality compared to APB.
Conclusions:
- Significant differences in axonal excitability exist along the human upper limb's median nerve, even when stimulating at a single site and recording from different muscles.
- Normal excitability values derived from one muscle group (e.g., APB) are not interchangeable with those from another (e.g., FCR).
- These findings are vital for accurate interpretation of nerve excitability studies in patients, particularly those with central nervous system disorders affecting the FCR.
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