Motor patterns associated with crawling in a soft-bodied arthropod

Abstract

SUMMARYSoft-bodied animals lack distinct joints and levers, and so their locomotion is expected to be controlled differently from that of animals with stiff skeletons. Some invertebrates, such as the annelids, use functionally antagonistic muscles (circumferential and longitudinal) acting on constant-volume hydrostatics to produce extension and contraction. These processes form the basis for most theoretical considerations of hydrostatic locomotion in organisms including larval insects. However, caterpillars do not move in this way, and their powerful appendages provide grip independent of their dimensional changes. Here, we show that the anterograde wave of movement seen in the crawling tobacco hornworm, Manduca sexta, is mediated by co-activation of dorsal and ventral muscles within a body segment, rather than by antiphasic activation, as previously believed. Furthermore, two or three abdominal segments are in swing phase simultaneously, and the activities of motor neurons controlling major longitudinal muscles overlap in more than four segments. Recordings of muscle activity during natural crawling show that some are activated during both their shortening and elongation. These results do not support the typical peristaltic model of crawling, but they do support a tension-based model of crawling, in which the substrate is utilized as an anchor to generate propulsion.

Flexible parylene-based microelectrode arrays for high resolution EMG recordings in freely moving small animals

“…This activity could be defined as separate EJP events to reveal patterns of motor neuron firing during each type of movement. These recordings provide much finer discrimination of muscle activity than is currently available using fine wires (Simon et al, 2010). A comprehensive series of experiments is currently underway to understand how such motor patterns relate to specific movements.…”

Scaling of caterpillar body properties and its biomechanical implications for the use of a hydrostatic skeleton

“…For structures consisting of muscles, the muscles can act as both the structural support and the actuator (muscular hydrostats) (Kier, 1992). Although an alternative locomotion strategy based on the controlled release of tension has recently been proposed (Lin and Trimmer, 2010;Simon et al, 2010), it is limited to substrates that are stiffer than the animal. Directed movements on soft media and behaviors involving single point attachments must involve body stiffening, mostly through hydrostatics.…”

Mathematical model of inchworm locomotion

“…Caterpillar bodies are segmented, with intersegmental membranes connecting the segments [2]. Many caterpillars exhibit crawling motions that involve arching of a small part of the body, with the arched portion moving in a wave toward the head [8,11,[15][16][17][18][19][20][21][22][23]. Inchworms do not contain some of the central prolegs that exist in crawling caterpillars, and inchworm locomotion includes arching that involves much of the length of the body (Fig.…”