Basis Of Locomotion Research Articles

A lumped parameter model of endoplasm flow in Physarum polycephalum explains migration and polarization-induced asymmetry during the onset of locomotion.

The plasmodial slime mold Physarum polycephalum exhibits strong, periodic flow of cytoplasm through the veins of its network. In the special case of mesoplasmodia, a newly described starvation-induced, shape-constant morphotype, this periodic endoplasm streaming is the basis of locomotion. Furthermore, we presume that cytoplasm flow is also involved in signal transmission and signal processing. Mesoplasmodia motility resembles amoeboid locomotion. In contrast to other amoebae, however, mesoplasmodia move without extending pseudopods and retain a coherent, fan-shaped morphology throughout their steady locomotion. Attaining sizes of up to 2 mm2, mesoplasmodia are also much bigger than other amoebae. We characterize this particular type of locomotion and identify patterns of movement. By using the analogy between pulsatile fluid flow through a network of elastic tubes and electrical circuits, we build a lumped model that explains observed fluid flow patterns. Essentially, the mesoplasmodium acts as a low-pass filter, permitting only low-frequency oscillations to propagate from back to front. This frequency selection serves to optimize flow and reduces power dissipation. Furthermore, we introduce a distributed element into the lumped model to explain cell polarization during the onset of chemotaxis: Biochemical cues (internal or external) lead to a local softening of the actin cortex, which in turn causes an increased flow of cytoplasm into that area and, thus, a net forward movement. We conclude that the internal actin-enclosed vein network gives the slime mold a high measure of control over fluid transport, especially by softening or hardening, which in turn leads to polarization and net movement.

13.3. The adaptive basis of locomotion in terrestrial and arboreal lizards: Mechanistic and ecological approaches

13.3. The adaptive basis of locomotion in terrestrial and arboreal lizards: Mechanistic and ecological approaches

The Optics and Actions of Catching Fly Balls: Zeroing Out Optical Acceleration

Advancing or retreating so as to maintain a projectile's constant vertical optical velocity was suggested by Chapman (1968) as a possible basis for locomotion in ball catching. Three experiments examined this thesis. In Experiments I and 2, the positions of balls and catchers were videotaped to see if the movements of the catchers canceled optical acceleration. Such canceling was indeed observed until just prior to the catch for hand-thrown balls (Experiment 1). The monocular availability of the information predicts success with monocular viewing, confirmed in Experiment 2 with machine-thrown balls. In Experiment 3, observers judged whether a ball (represented as a moving dot on a computer screen) would land at, in front of, or behind them. Performance was above chance, but only some observers used acceleration. Together, the experiments provide broad, though not unequivocal, support for the utilization of optical acceleration to guide locomotion in catching.

Hypothalamic autostimulation of rats in response to low-frequency stimulation on a basis of locomotion

Hypothalmic autostimulation of rats was studied in response to low-frequency stimulation at the rate of 30 to 7 Hz. The animals received brain stimulation in Skinner's chamber and on the basis of locomotion. The duration of the volleys of pulses as established by the animals during autostimulation on the basis of locomotion increased with a decrease in stimulus frequency. The pauses between the volleys and the duration of the volleys themselves increased with a decrease in stimulus strength. With stimulation at 7 Hz it was possible to choose a strength of current at which the total duration of the pauses was less than 10% of the total time of the experiment. Usually under these circumstances the duration of the individual pauses was less than 0.5 sec.

Conditioning the cardiorespiratory dynamics of locomotion in dogs.

In 17 dogs blood pressure in the carotid artery, heart rate, pneumogram and actogram of the hind leg were recorded during rest and during locomotion on a treadmill. The increases in cardiorespiratory dynamics which occurred during locomotion were then conditioned. The conditional stimulus was represented by the noise and vibration of the treadmill. It was determined that conditional changes in cardiorespiratory dynamics can be formed quickly on the basis of locomotion. Qualitatively the changes were the same as the unconditional changes, and their magnitude was 60 to 70 per cent that of the unconditional changes. Conditional increase in cardiorespiratory dynamics was most intensive in the first 30 seconds from the onset of the conditional stimulus. In acute extinction of these conditional changes, movements of the extremities were inhibited first, followed by inhibition of increased blood pressure, then inhibition of increased heart rate, and last, inhibition of increased respiratory rate.