Abstract
The responsiveness of the human central nervous system can change profoundly with exercise, injury, disuse, or disease. Changes occur at both cortical and spinal levels but in most cases excitability of the motoneuron pool must be assessed to localize accurately the site of adaptation. Hence, it is critical to understand, and employ correctly, the methods to test motoneuron excitability in humans. Several techniques exist and each has its advantages and disadvantages. This review examines the most common techniques that use evoked compound muscle action potentials to test the excitability of the motoneuron pool and describes the merits and limitations of each. The techniques discussed are the H-reflex, F-wave, tendon jerk, V-wave, cervicomedullary motor evoked potential (CMEP), and motor evoked potential (MEP). A number of limitations with these techniques are presented.
Highlights
The motoneuron was described as the “final common path” of the nervous system (Sherrington, 1906) and has been a focal point of neuroscience research for over a century
Since the introduction of the terminology, the designation of “final common path” has been frequently expanded to include the α-motoneuron and the muscle fibers which it innervates (e.g., Denslow and Hassett, 1942). This expanded definition is sensible from a functional perspective because movement requires contraction of muscle fibers and the properties of muscle fibers are largely dictated by the properties of the motoneuron which innervates them
Before we discuss the most common methods used to test excitability of the human motoneuron pool, it is first necessary to define our use of the term “excitability” in this review
Summary
The responsiveness of the human central nervous system can change profoundly with exercise, injury, disuse, or disease. Changes occur at both cortical and spinal levels but in most cases excitability of the motoneuron pool must be assessed to localize accurately the site of adaptation. It is critical to understand, and employ correctly, the methods to test motoneuron excitability in humans. Several techniques exist and each has its advantages and disadvantages. This review examines the most common techniques that use evoked compound muscle action potentials to test the excitability of the motoneuron pool and describes the merits and limitations of each. A number of limitations with these techniques are presented
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