Constraints on the deformation of the vibrissa within the follicle
Fig 7
Caudal deflection and actuated intrinsic muscles result in increased whisker displacement.
(A) The middle panel illustrates the follicle at rest, with superficial tissue (ST) indicated by thin hatching and deep tissue (DT) indicated by coarse hatching. Illustrations in left and right panels show the directions of the reaction forces on the vibrissa when the whisker is deflected rostrally and caudally, respectively. The external force is in black, and the reaction forces are in red. L: lateral; R: rostral; MusR: rostral intrinsic muscle; MusC: caudal intrinsic muscle. (B) Illustrations show muscle behavior in four different cases. Each illustration shows two follicles and the connecting intrinsic muscles. The caudal of the two whiskers is deflected in either the rostral direction (left column) or caudal direction (right column), during both passive touch (blue box) and active whisking (orange box). Muscles are defined to be completely relaxed (blue) during passive touch, and actuated (orange) during active whisking. During passive touch, the whisker is deflected by an external peg, marked by a black circle. During active whisking, the caudal follicle retracts/protracts against a peg, so that the whisker is deflected rostrally/caudally. The locations of two external springs, k5 and k6, are indicated in the two middle panels. (C) A table qualitatively summarizes intrinsic muscle stiffness for different cases of muscle activation and deflection direction. Asterisks indicate the ordinal (not proportionally scaled) magnitudes of muscle stiffness. (D) A table qualitatively summarizes k5 and k6 stiffness for different cases of muscle activation and deflection direction. Asterisks indicate the ordinal (not proportionally scaled) magnitudes of muscle stiffness. (E) The change in relative displacement r(x) under different overall external spring stiffness (k5+k6). The overall stiffness increases logarithmically from 104N/m (blue) to 105N/m (orange). A stiffer external support results in bigger r(x). (F) The identical plot as (E), but with different external spring stiffness ratios (k5/k6). As the ratio shifts from unbalanced (blue) to balanced (orange), larger r(x) is observed at the RS level.