ABSTRACT
The musculoskeletal model of cat's hind limbs, capable to step while maintaining balance, was developed using the MatLab. The skeletal part of the model (spine, pelvis, hips, shanks, foots) was created at SimMechanics. The joint in the spine attachment to the support and hip joint have three degrees of freedom. Knee and ankle joints have one degree of freedom. The pelvis is rigidly connected to the spine. The control of the skeleton's segments is done by six groups of muscles (flexors and extensors of hips, knees and ankles), modeled using the package VirtualMuscle. The generalized lateral force exerted on the spine was introduced to compensate insecure lateral deviations. Experimental verification of the model realness have shown that its locomotor characteristics (e. g., muscles activation patterns, oscillation period of pelvis, correlation between step length and maximal lateral shift of pelvis) do not significantly differ from the locomotion of decerebrate cats. The simulation confirms the key role of lateral force evolved by paravertebral and abductor-adductor muscles in the control of lateral stability during locomotion.
Subject(s)
Hindlimb/physiology , Locomotion/physiology , Models, Biological , Muscle Contraction/physiology , Muscle, Skeletal/physiology , Postural Balance/physiology , Animals , Biomechanical Phenomena , Cats , Computer Simulation , Decerebrate State , Electromyography , Hindlimb/anatomy & histology , Mathematics , Muscle, Skeletal/anatomy & histology , Weight-Bearing/physiologyABSTRACT
We have found that the brainstem-spinal cord circuitry of decerebrated cats actively maintain the equilibrium during standing, walking and imposed mechanical perturbations similar to that observed in intact animals. The corrective hindlimb motor responses during standing included redistribution of the extensor activity ipsilateral and contralateral to perturbation. The postural corrections in walking cats were due to considerable modification of EMG pattern in the limbs as well as changing of the swing-stance phases of the step cycle and ground reaction forces depending of perturbation side. Thus the basic mechanisms for balance control of decerebrated animals in these two forms of motor behavior are different. Balance-related adjustments relied entirely on the integration of somatosensory information arising from the moving hindquarters because of the suppression of vestibular, visual, and head-neck-trunk sensory input. We propose that the somatosensory input from the hindquarters in concert with the lumbosacral spinal circuitry can control the dynamics of the hindquarters sufficient to sustain balance. We found that, after isolation from the brainstem or forebrain, lumbosacral circuits receiving tonic epidural electrical stimulation can effectively control equilibrium during standing and stepping. Detailed analyses of the relationships among muscle activity, trunk kinematics, and limb kinetics indicate that spinal motor systems utilize a combination of feedback and feedforward strategies to maintain dynamic equilibrium during walking. The unexpected ability of spinal circuitries to exert efficient postural control in the presence of epidural electrical stimulation in decerebrated and spinal cats have significant implications for the potential of humans with a severe spinal cord injury to regain a significant level of functional standing and walking capacities.
Subject(s)
Decerebrate State/physiopathology , Gait/physiology , Locomotion , Neurons/physiology , Posture/physiology , Spinal Cord/physiology , Animals , Cats , Cerebral Cortex/physiology , Cerebral Cortex/surgery , Electric Stimulation , Electromyography , Hindlimb/physiology , Hindlimb/physiopathology , Microelectrodes , Muscle, Skeletal/physiology , Neurosurgical Procedures , Stereotaxic TechniquesABSTRACT
It is known that spinal neuronal networks activated by epidural electrical stimulation (EES) can produce the stepping EMG pattern and control the locomotor behavior. At present study we showed that non-invasive transcutaneous electrical spinal cord stimulation (tESCS) applied to the lumbar-sacral enlargement can facilitate the locomotor activity in decerebrated and spinal animals. The comparison of the motor responses evoked by EES vs tESCS showed that both methods produce the locomotor patterns with close properties and similar reflex mechanisms. The data obtained suggest that tESCS is an efficient approach for investigation of the locomotor control in acute and chronic experiments as well as facilitates of the locomotor abilities after spinal cord injury. Taking to account the non-invasivity and easement of tESCS, this approach could be further implemented in clinical practice for rehabilitation of the patient with spinal cord injury.
