C. Duch et Hj. Pfluger, MOTOR PATTERNS FOR HORIZONTAL AND UPSIDE-DOWN WALKING AND VERTICAL CLIMBING IN THE LOCUST, Journal of Experimental Biology, 198(9), 1995, pp. 1963-1976
The motor patterns of the locust's flexor tibiae and metathoracic subc
oxal joint muscles were compared during unrestrained horizontal walkin
g, vertical climbing and walking upside-down hanging from a branch, Co
mbining anatomical and structural data with the results from myographi
c recordings revealed the role of these muscles during walking and the
ir functional adjustments to different loads and gravity effects cause
d by changes in walking conditions, Motor patterns are remarkably cons
tant during a given walking situation even at quite different walking
speeds, In all walking situations, changes in step duration correlate
strongly with changes in the duration of retraction but only weakly wi
th the duration of protraction, Different motor units of one muscle ca
n be distinguished by their spike amplitude, They may be active simult
aneously or they may alternate and then fire in different phases of th
e step cycle, For example, during horizontal walking, the small unit o
f the first abductor (M125) is active during protraction and the large
one during retraction, During retraction, the coral muscles serve two
functions: (1) the joint has to be brought back to the posterior extr
eme position by retractor muscles; (2) the joint has to be stabilized,
that is held 'stiffly', by co-activity of functional antagonists, Dur
ing protraction, it is moved to the anterior extreme position by power
ful contractions of protractor muscles, The muscular activity patterns
show marked differences depending on the walking situation, Some larg
e motor units spike only sporadically during horizontal walking but bu
rst during vertical climbing and upside-down walking (muscle M121p, th
e large units of muscles M126 and M120). During upside-down walking, m
uscles M120 and M121 and the large unit of muscle M125 are active duri
ng opposite phases of the step cycle when compared with horizontal wal
king and vertical climbing (for example, during walking and climbing,
muscle M120 is active at the transition between retraction and protrac
tion, whereas during upside-down walking, activity occurs during late
protraction and early retraction). The results describe how motor patt
erns are adjusted to the different requirements of various walking sit
uations.