title: Compartmentalized innervation of primate lateral rectus muscle.
abstract: OBJECTIVE
  Skeletal and craniofacial muscles are frequently composed of multiple neuromuscular compartments that serve different physiological functions. Evidence of possible regional selectivity in LR intramuscular innervation was sought in a study of the anatomic potential of lateral rectus (LR) muscle compartmentalization.
  
  
  METHODS
  Whole orbits of two humans and five macaque monkeys were serially sectioned at 10-microm thickness and stained with Masson trichrome. The abducens nerve (CN6) was traced anteriorly from the deep orbit as it branched to enter the LR and arborized among extraocular muscle (EOM) fibers. Three-dimensional reconstruction was performed in human and monkey orbits.
  
  
  RESULTS
  Findings were in concordance in the monkey and human orbits. External to the LR global surface, CN6 bifurcated into approximately equal-sized trunks before entering the global layer. Subsequent arborization showed a systematic topography, entering a well-defined inferior zone 0.4 to 2.5 mm more posteriorly than branches entering the largely nonoverlapping superior zone. Zonal innervation remained segregated anteriorly and laterally within the LR.
  
  
  CONCLUSIONS
  Consistent segregation of intramuscular CN6 arborization in humans and monkeys suggests functionally distinct superior and inferior zones for the LR. Since the LR is shaped as a broad vertical strap, segregated control of the two zones could activate them separately, potentially mediating previously unappreciated but substantial torsional and vertical oculorotary LR actions.
authors.affiliation: Department of Ophthalmology, University of California, Los Angeles, Los Angeles, CA 90095-7002, USA.
authors.forename: Michelle
authors.initials: M
authors.lastname: Peng
authors.forename: Vadims
authors.initials: V
authors.lastname: Poukens
authors.forename: Roberta Martins
authors.initials: RM
authors.lastname: da Silva Costa
authors.forename: Lawrence
authors.initials: L
authors.lastname: Yoo
authors.forename: Lawrence
authors.initials: L
authors.lastname: Tychsen
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Demer
mesh_terms: D000010:Abducens Nerve / Q000033:anatomy & histology*; D000818:Animals; D002102:Cadaver; D006801:Humans; D021621:Imaging, Three-Dimensional; D008251:Macaca; D009119:Muscle Contraction / Q000502:physiology; D009801:Oculomotor Muscles / Q000294:innervation* / Q000502:physiology*; D009915:Orbit / Q000033:anatomy & histology; D013194:Staining and Labeling; D054159:Torsion, Mechanical