Anat Rec (Hoboken). 2010 July; 293(7): 1192-206
Muscle architecture in the mystacial pad of the rat.
Haidarliu S, Simony E, Golomb D, Ahissar E.
The vibrissal system of the rat is an example of active tactile sensing, and has recently been
used as a prototype in construction of touch-oriented robots. Active vibrissal exploration and
touch are enabled and controlled by musculature of the mystacial pad. So far, knowledge
about motor control of the rat vibrissal system has been extracted from what is known about
the vibrissal systems of other species, mainly mice and hamsters, since a detailed
description of the musculature of the rat mystacial pad was lacking. In the present work, the
musculature of the rat mystacial pad was revealed by slicing the mystacial pad in four
different planes, staining of mystacial pad slices for cytochrome oxidase, and tracking spatial
organization of mystacial pad muscles in consecutive slices. We found that the rat mystacial
pad contains four superficial extrinsic muscles and five parts of the M. nasolabialis
profundus. The connection scheme of the three parts of the M. nasolabialis profundus
is described here for the first time. These muscles are inserted into the plate of the mystacial pad,
and thus, their contraction causes whisker retraction. All the muscles of the rat mystacial
pad contained three types of skeletal striated fibers (red, white, and intermediate). Although
the entire rat mystacial pad usually functions as unity, our data revealed its structural
segmentation into nasal and maxillary subdivisions. The mechanisms of whisking in the rat,
and hypotheses concerning biomechanical interactions during whisking, are discussed with respect
to the muscle architecture of the rat mystacial pad.