Content area
Full Text
Recent advances in integrative studies of locomotion have revealed several general principles. Energy storage and exchange mechanisms discovered in walking and running bipeds apply to multilegged locomotion and even to flying and swimming. Nonpropulsive lateral forces can be sizable, but they may benefit stability, maneuverability, or other criteria that become apparent in natural environments. Locomotor control systems combine rapid mechanical preflexes with multimodal sensory feedback and feedforward commands. Muscles have a surprising variety of functions in locomotion, serving as motors, brakes, springs, and struts. Integrative approaches reveal not only how each component within a locomotor system operates but how they function as a collective whole.
Locomotion, movement through the environment, is the behavior that most dictates the morphology and physiology of animals. Evolutionary pressures for efficient, rapid, adjustable, or just plain reliable movement often push the envelope of organism design. Biologists have long been attracted to locomotor extremes because they provide especially clear examples from which to determine structure-function relations. It is not a coincidence, for example, that David Keilin first discovered cytochromes within insect flight muscle, a tissue that exhibits the highest known metabolic rate, or that J. Z. Young discovered a giant axon in a squid, an animal capable of rapid escape responses through jet propulsion. Other fundamental discoveries regarding central pattern generators, visual processing, skeletal remodeling, and many other important physiological phenomena originated from studies of locomotion. Locomotion is not, however, the simple net outcome of isolated specializations in individual cells and tissues. Although it is possible to deconstruct the mechanics of locomotion into a simple cascade-- brain activates muscles, muscles move skeleton, skeleton performs work on external world-such a unidirectional framework fails to incorporate essential dynamic properties that emerge from feedback operating between and within levels. One key challenge in the study of locomotion is to determine how each individual component within a locomotor system operates, while at the same time discovering how they function collectively as an integrated whole.
An integrative approach to locomotion focuses on the interactions between the muscular, skeletal, nervous, respiratory, and circulatory systems. These systems possess functional properties that emerge only when they interact with each other and the environment. Frequently, model organisms are chosen because they perform some function exceptionally well. When performance is...