HUMAN FACIAL-MUSCLES - DIMENSIONS, MOTOR END-PLATE DISTRIBUTION, AND PRESENCE OF MUSCLE-FIBERS WITH MULTIPLE MOTOR END-PLATES

Background: Extrafusal muscle fibers of human striated skeletal muscle s are known to have a uniform innervation pattern. Motor endplates (ME P) of the ''en plaque'' type are located near the center of muscle fib ers and distributed within the muscles in a narrow band. The aim of th is study was to evaluate the innervation pattern of human facial muscl es and compare it with that of skeletal muscles. Methods: Ten facial m uscles from 11 human cadavers were dissected, the nerve entrance point s located, and the dimensions measured, All muscles were stained in to te for MEPs using Acetylcholinesterase (AChE) and examined under the m icroscope to determine their location, Single muscle fibers were tease d to evaluate the stained MEPs, Results: The length of the different f acial muscles varied from 29 to 65 mm, which correlated to the length of the corresponding muscle fibers, MEP zones were found on the muscle s in the immediate vicinity of the nerves' entrance points and located eccentrically. Numbers and locations varied from muscle to muscle. Th ree MEP zone distribution patterns were differentiated: numerous small MEP zones were evenly spread over the muscle, a predominant MEP zone and two to three small zones were spread at random, and two to four ME P zones of equal size were randomly scattered. One MEP of the ''en pla que'' type was found in 73.8% of the muscle fibers and two to five MEP s were found in 26.2%. The distances between the multiple MEPs on one muscle fiber varied from 10 to 500 mu m. Conclusions: This study sugge sts that facial muscles differ from skeletal muscles regarding distrib ution and number of MEPs. The eccentric location of MEP zones and mult iple MEPs suggests there is an independent mechanism of neural regulat ion in the facial muscle system. (C) 1997 Wiley-Liss, Inc.