iWorx Systems, Inc.
September 2014 eNewsletter

Experiment
Median Nerve Conduction Velocity

Lab written in conjunction with:
Nathan Heller, Undergraduate research assistant; Kathryn Forti, Undergraduate research assistant; Keith K. Schillo, PhD, Associate Professor, Biology Department, SUNY Oneonta,Oneonta, NY

The median nerve is one of the major peripheral nerves of the upper limb. The nerve roots associated with this nerve are from C6-T1. Motor functionality includes innervating the flexor muscles in the anterior compartment of the forearm with the exception of the flexor carpi ulnaris and part of the flexor digitorum profundus, which are innervated by the ulnar nerve and also supplies innervation to the thenar muscles and lateral two lumbricals of the hand. The sensory functions of the median nerve include the palmar cutaneous branch, which innervates the lateral part of the palm, and the digital cutaneous branch, which innervates the lateral three and a half fingers on the anterior (palmar) surface of the hand. Thus, this nerve is primarily responsible for the sensations in the palm of your hand and the first 3.5 digits including your thumb.

The median nerve originates from the brachial plexus in the axilla (armpit), moves down the arm lateral to the brachial artery and, at approximately halfway down the arm, the nerve crosses over the brachial artery, and sits medially. In the forearm, the nerve travels between the flexor digitorum profundus and flexor digitorum superficialis muscles. The median nerve gives rise to two major branches in the forearm:

• Anterior interosseous nerve - which supplies the deep muscles in the anterior forearm.
• Palmar cutaneous nerve - which innervates the skin of the lateral palm.

The nerve then enters the hand via the carpal tunnel, where it terminates by dividing into two branches:

• Recurrent branch - which innervates the thenar muscles, the group of muscles associated with the lower palm and thumb.
• Palmar digital branch - which innervates the palmar surface and fingertips of the lateral three and half digits and the lateral two lumbrical muscles.

The interesting thing about the median nerve is its clinical relevance to Carpal Tunnel Syndrome (CTS). Compression of this nerve leads to one of the most common neuropathies and can be caused by thickened ligaments and tendon sheaths. Patients often comment on numbness, tingling and pain in the area of the median nerve which can radiate to the forearm. Symptoms can wake the patient from their sleep and are generally worse in the mornings. If left untreated, CTS can cause weakness and atrophy of the thenar muscles.

One of the tests for CTS is Median Nerve Conduction Velocity, by looking at the speed of transmission of the response to the stimulation of the nerve. In this lab, students will perform MNCV tests on subjects to gain an understanding of how age, gender and handedness can play a role in how the nerve performs.

Web Resources

More information on kinesiology and targeted muscle EMG, as well as additional external physiology-related links.

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