Locomotion among animals has captured man’s imagination for centuries. My students and I are no exception. Our studies of anatomy, physiology and behavior are designed to reveal fundamental mechanisms of limb coordination in vertebrate animals. These studies span the analysis of bird wings and their control during flight to the intricacies of nerve regeneration. We examine limb movement patterns, the design and contractile properties of muscle, and spinal cord organization by applying techniques that reveal form and function.

Peripheral nerve regeneration. Mr. Sam Poore, in his final year as an MD/Ph.D student, is consumed in preparing for publication an unexpected mismatch between the time course of nerve-muscle recovery and locomotor performance detected in his studies of peripheral nerve injury.

Creative writing project. Ms. Christine Montross, a third-year medical student and candidate for the Master of Medical Science degree, is writing a creative nonfiction book about the experience of dissecting a human cadaver. Christine intends to recount the process and answer that “What is it like?” question, but also to explore how medical students are transformed from people with experiences not so different from their roommates and neighbors to people who know the heft of the liver, or the odd consistency of the pancreas.

Wing-propelled diving. Ms. Jonna Hamilton, a third year Ph.D. student, spends time each day training Thick-billed Murres in pursuit of her interests in wing-propelled diving.

Wing control in birds. Several recent studies in our laboratory that involve undergraduate and graduate students focus on the functional anatomy of the shoulder of birds. Wind tunnels, muscle function and spinal cord organization are the fare. Fascinating experiments!

Wing elevation. Initiated as an undergraduate project, we made physiological measurements in two species of birds of the forces exerted on the humerus by a major shoulder muscle, the supracoracoideus, generally assumed to simply ‘elevate’ the wing during upstroke. We determined that more important than wing elevation, the supracoracoideus imparts a high-velocity rotation to the humerus about its longitudinal axis which is the action that really prepares the wing for the next downstroke. This reinterpretation of the muscle’s primary action in all birds provides insight into the selective advantage of this muscle’s unique organization in the evolution of powered flapping flight.

Motor unit organization. Led by Alan Sokoloff, now at Emory University, we are engaged in studies of how the smallest functional component of nerve and muscle, the motor unit, is used in bird flight. We study the downstroke muscle, pectoralis, of pigeons within which two populations of motor units exist. Evidence from studies of muscle function in other vertebrates strongly suggests that the order in which motor units are selected by the nervous system for increased force is determined by the specific synaptic properties of each motorneuron that relates to its size. Our findings in pigeons suggest that perhaps other rules are at play. Two populations of motor units are found, one that is organized to produce substantial force and power for takeoff, landing and other ballistic movements whereas a second distinct population is suited for sustained flight when power requirements are reduced. Surprisingly, the muscle fibers of both units are arranged within the pectoralis in-series; i.e., more than one fiber is required to span the origin-to-insertion distance. This organization is in contrast to that reported for most mammalian muscles and poses particular problems regarding the muscle's neural control.

Evolutionary conservation of neuromotor pattern. The neuromotor pattern (i.e. the onset/offset of muscle contraction within the locomotor cycle) is conserved for some homologous muscles of the tetrapod shoulder but not others in the transition from terrestrial locomotion to flight. Our research associate Mr. Don Wilson, now at the Mayo Clinic, led us into an examination of the motor pool organization and histochemical composition of the flight muscles of European starlings to explore “the rules” governing these patterns. We tested for three shoulder muscles whether retention of, or deviation from, a conserved neuromotor pattern can be predicted on the basis of the location of the muscle’s motor nucleus within the motor column and the histochemical profile of its constituent muscle fibers. We found that an evolutionary change in neuromotor pattern can occur without a corresponding topological reorganization of a muscle’s motor nucleus within the motor column. Nor can the histochemical profile of homologous muscles be used to predict their neuromotor pattern in the transition from terrestrial locomotion to flight. These findings suggest that evolutionary change in neuromotor outflow relates to altered synaptic input from supraspinal or segmental sources or by alteration of factors intrinsic to individual motoneurons. Follows up studies are in progress.

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