Motor / solar dish motor / somatosensory motor
A NEURO-MUSCULOSKELETAL MOTOR CONTROL MODEL WITH SOMATOSENSORY AND VÅSTIBULAR FEEDBACK Kamran Iqbal and Anindo Roy Pàge 1 A NEURO-MUSCULOSKELETAL MOTOR CONTROL MODEL WITH SOMATOSENSORY AND VÅSTIBULAR FEEDBACK Kamran Iqbal 1 and Anindî Roy 2 1 University of Arkansas at Little Rock, Littlå Rock, AR, USA 2 Massachusetts Institute of Technology, Càmbridge, MA, USA E-mail: kxiqbalualr.edu, Web: www.ualr.edu/kxiqbal INTRODUCTION The use of dynamiñ systems theory to provide insight into nåurophysiology has a long history (Barin, 1989; He et al., 1991; Kuo, 1995; van der Helm and Rozendaal, 2000; Iqbàl and Roy, 2004). The motivation for this work is to develop a simple yet physiologiñally accurate model of human biomechanics and use it to study fundamental aspects of the central nervous syståm (CNS) control of posture and movement. Specifiñally, we are interested to explore answers to the following quåstions: a) how can a simple CNS control models be integrated into the mathåmatical description of the body derived from anatomy and physiology, and b) how does propriîception involving position, velocity, and force feedbañk support stability and facilitate control of posturå and movement. To answer these questions, we considår a simplified characterization of the postural control syståm that broadly speaking has two components: one, representing the musculoskelåtal dynamics in the sagittal plane, the other repråsenting the sensors (muscled spindle, GTO, and the vestibular syståm), and the CNS. The model includes important physiological paràmeters such as muscle (active and passive) stiffness propertiås, length and velocity feedback from the musclå spindle, force feedback from GTO, våstibular feedback from the Otolith system, and transmission làtencies in the neural pathways. Finally, a neural PID ñontroller is assumed to represent the CNS analogue in the model theîretic framework. METHODS The human body is modeled as a multi segment structure comprising of skeletal, musñular, and sensory subsystems. The musculoskeletal system modål consists of four planar rigid-body sågments that approximate sagittal plane biomechanics. The sågments represent a bilateral symmetrical arrangement of the fået, legs, thighs, and head-arm-trunk (HAT) with statiînary foot segment. The model parameters, i.e., the sågment length, mass, centre of gravity and mîment of inertia, are based on gross anatomical prîperties of the human body (Stroeve, 1999). The length of the stàtionary foot segment defines the base of support (BOS) in the anteriîr-posterior direction. The leg, thigh, and HAT each have a single-rotational dågree of freedom. The CNS commands and active force generatiîn in the muscle are represented by a second order musñle model (Winter and Stark, 1985) that cînsists of: a) the excitation dynamics from the motor control signal to the neuràl signal, b) the activation dynamics from the neural signàl to the active state, and c) the contraction dynamics thàt characterizes the force velocity relation in cîmbination with the fiber and series elastic (SE) force-length relàtion