SPINAL-CORD COORDINATION OF HINDLIMB MOVEMENTS IN THE TURTLE - INTRALIMB TEMPORAL RELATIONSHIPS DURING SCRATCHING AND SWIMMING

Spinal cord neuronal circuits generate motor neuron activity patterns responsible for rhythmic hindlimb behaviors such as scratching and swi mming. Kinematic analyses of Limb movements generated by this motor ne uron output reveal important characteristics of these behaviors. Intra limb kinematics of the turtle hindlimb were characterized during five distinct rhythmic forms of behavior: three forms of scratching and two forms of swimming. In each movement cycle for each form, the angles o f the hip and knee joints were measured as well as the tinting of a be havioral event, e.g., rub onset in scratching or powerstroke onset in swimming. There were distinct differences between the kinematics of di fferent forms of the same behavior, e.g., rostral scratch versus pocke t scratch. In contrast, there were striking similarities between forms of different behaviors, e.g., rostral scratch versus forward swimming . For each form of behavior there was a characteristic angular positio n of the hip at the onset of each behavioral event (rub or powerstroke ). The phase of the onset of knee extension within the hip position cy cle occurred while the hip was flexing in the rostral scratch and forw ard swim and while the hip was extending in the pocket scratch, caudal scratch, and back-paddling form of swimming. The phase of the onset o f the behavioral event was not statistically different between rostral scratch and forward swim; nor was it different between pocket scratch and caudal scratch. These observations of similarities at the movemen t level support the suggestion that further similarities, such as shar ed spinal circuitry, may be present at the neural circuitry level as w ell.