Measuring Compound Muscle Action Potentials by Stimulating the Phrenic Nerve in a Rat

Take an anesthetized rat implanted with stimulating electrodes at the base of the neck, near the phrenic nerve's descending path to the diaphragm.

The electrodes are used to stimulate the phrenic nerve, which innervates the diaphragm, and triggers its contraction during inhalation.

A recording electrode monitors the electrical activity from the diaphragm muscles, while a reference electrode establishes baseline signals, and a ground electrode reduces signal noise.

Apply a high-intensity electric pulse that generates action potentials in all motor neurons inside the phrenic nerve.

The action potentials propagate to the neuromuscular junction and induce the release of neurotransmitters.

The neurotransmitters bind to receptors on muscle fibers, triggering action potentials that cause muscle contraction.

Record the aggregate electrical activity from multiple muscle fibers, termed compound muscle action potentials or CMAPs, to obtain the response curve, preceded by an artifact peak resulting from the electrical stimulation.