Experimental strategies for identifying suitable mechanical models of the head-neck system

Musculoskeletal systems in humans and other vertebrates can be difficult to model realistically because their many elements have diverse and specialized properties. Computer graphical tools are now available that can organize the large numbers of parameters needed to quantify articular relationships and muscle attributes in a particular motor system. However, such models may be overly complex for the general use of scientists and engineers whose interests are directed at the control principles underlying particular movements. Thus, approaches must be developed to simplify the detailed models in ways that capture the relevant features of the system but reduce the level of morphological and computational complexity. The authors are using three methods to simplify models of the feline head-neck system that can be used to describe visually guided head movements in the horizontal and vertical planes. 1. Videofluoroscopy is used to identify patterns of joint motion that occur during head movements in particular planes. 2. Electromyographic recordings are used to identify which of the more than two dozen neck muscles are active during the same head movements. 3. Anatomical dissections and geometric representations are used to gain insight into the torque-generating capabilities of muscles in different head-neck postures. These approaches taken together have helped to identify structures that might be collapsed or eliminated in simpler models to describe these movements. They have also helped to identify deficiencies in the more complex graphical models that are currently under development.