Exploring Properties of Motor Units From Motor Neuron to Muscle Fibers

TOPICAL COLLECTIONS

Guest Editors

Gary Sieck

Mayo Clinic

Gary C. Sieck, PhD is an endowed professor and distinguished investigator in the Department of Physiology and Biomedical Engineering at Mayo Clinic. He served as Department Chair and Dean for Academic Affairs at Mayo. He has mentored 27 PhD students and 87 postdoctoral fellows. He was president of the American Physiological Society and president of the Association of Chairs of Departments of Physiology. He is an elected fellow of the American Physiological Society and the American Institute of Medical and Biological Engineering. His research focuses on motor unit physiology, specifically neural control of respiratory muscles and his research has been continuously funded by multiple grants from the NIH for more than 45 years. He has authored 475 journal articles, numerous abstracts, and many other written publications. He was editor-in-chief of the Journal of Applied Physiology and Physiology and is currently an associate editor of Comprehensive Physiology and FASEB BioAdvances.

Obaid Khurram

Department of Physiology & Biomedical Engineering, Mayo Clinic

Dr. Obaid Khurram received his PhD in Biomedical Engineering and Physiology from the Mayo Clinic Graduate School of Biomedical Sciences under the guidance of Dr. Carlos Mantilla. His dissertation focused on characterizing the extent of functional motor deficits in various rat models of phrenic motor neuron loss. He then joined the lab of Dr. CJ Heckman at Northwestern University, where he studied the effects of neuromodulatory influences and persistent inward currents on motor unit discharge patterns in human limb muscles. He is currently a research associate in the lab of Dr. Gary Sieck, working primarily on understanding the impact of spinal cord injury on respiratory motor unit output. His work uses compound EMG, motor unit recordings, and pressure measurements to assess diaphragm muscle activity that sheds light on mechanisms governing the inspiratory and expiratory phases of the breath.

Matthew Fogarty

Mayo Clinic

Matthew J. Fogarty, BVSc, PhD is an Assistant Professor whose research is focused on the neuromotor system, which comprises motor control centers in the cortex, brainstem and spinal cord, and the motor neurons which connect to muscle. Dr. Fogarty is actively researching the pathophysiology of various neurodegenerative motor disorders, including amyotrophic lateral sclerosis (ALS) and age-associated sarcopenia.Dr. Fogarty has extensive experience in evaluating animal models of disordered development, aging, and neurodegenerative disease using approaches that assess sub-cellular organelles (e.g., mitochondria and dendritic spines using high-resolution spinning-disc confocal microscopy), neuronal function (using patch-clamp), neuromuscular function (using electromyelography and nerve-muscle stimulations) and whole-body movement behaviors (include trans diaphragmatic pressure and plethysmography). Dr. Fogarty has made many contributions to the field, with 65 peer-reviewed Journal publications, many book chapters and other publications.

Collection Overview

The motor unit comprises a motor neuron and its constituent muscle fibers, representing a neuromechanical transducer that converts neural electrical commands into mechanical muscle force. Passive electrophysiological properties of motor neurons are essential determinants of motor neuron excitability and are dependent on motor neuron size (e.g., surface area). Accordingly, smaller motor neurons are recruited first, as explained by a key concept in neuromotor control, the Size Principle. Electrophysiological properties of motor neurons can be recorded directly but only in reduced preparations.

However, because of the tight coupling between the motor neuron and constituent muscle fiber, recording motor unit action potentials provides a window into motor neuron activity. Motor unit recruitment and activity can then be related directly to functional behaviors. Electromyography (EMG) is an established method to measure motor unit action potentials (individual or compound). Recent advances in EMG techniques allow simultaneous recording and analysis of numerous motor unit action potentials. Other novel methods have been introduced to measure the physical attributes (e.g., motor neuron surface area) and biochemical properties (e.g., energy production and enzymatic activities) of motor neurons and muscle fibers.

The goal of this Methods Collection is to provide a valuable resource for investigators to utilize established and novel experimental tools to explore motor neurons.