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. 2008 Mar 5;28(10):2409–2425. doi: 10.1523/JNEUROSCI.3229-07.2008

Figure 3.

Figure 3.

In each frog, wiping trials were evoked with the distal tendon of BI still intact (A) and with the tendon detached from the limb and secured to a vibrator (B). In the first set of trials, BI contracted isometrically and contributed to forces at the ankle, and, in the second set, BI contracted isometrically against the vibrator. In the second set of trials, BI did not contribute to forces recorded at the ankle. Typical data are shown. A, The averaged force vectors produced during wiping trials in a single frog with BI muscle intact and attached (B.I.) and then with BI detached (B.D.) are shown at 40 ms intervals in the top two rows of the top panel. In the bottom row of this panel, force vectors produced by vector subtraction of B.D. forces from B.I. forces are shown (Res for resultant). In the middle two panels, the averaged magnitude and direction of B.D. (thin solid lines), B.I. (thick solid lines), and Res (dotted lines) forces are shown. Direction is referenced to the axis shown as 0° in the bottom of Figure 2B. In the bottom panel, the rectified, filtered, and averaged EMGs for five muscles (ST, BI, IL, SM, and RI) are shown for B.D. (thin-lined shaded envelopes) and B.I. (thick-lined envelopes) trials. Averages were constructed from eight trials for each condition. BI detachment did not alter the motor pattern. The magnitude of wiping forces was reduced and the direction of forces altered after BI detachment. The resultant force vectors (i.e., the forces removed by BI detachment) were uniformly directed over time (160°). B, We tested whether the direction of the resultant force vectors over time was similar to the direction of forces produced by direct stimulation of BI (i.e., when intact, before detaching its tendon). The polar histograms show the distribution of force directions resulting from subtraction of BD from BI forces over a wiping trial (a 600 ms duration; top histogram) and the distribution of force directions obtained over a 600 ms duration of BI stimulation. Each bin represents 14.4°. The distributions were not significantly different (see Results). In the bottom panel, the mean direction produced by direct stimulation of the five muscles in A are shown. Force directions from stimulation of the BI, ST, RI, SM, and IL muscles in the limb configuration used here are diagrammed. Thus, detaching BI simply removes the BI force contribution at the ankle rather than compromising adjacent muscles or nerves.