title: Nonclassical innervation patterns in mammalian extraocular muscles.
abstract: OBJECTIVE
  The abducens (CN6) and oculomotor (CN3) nerves (nn) enter target extraocular muscles (EOMs) via their global surfaces; the trochlear (CN4) nerve enters the superior oblique (SO) muscle on its orbital surface. Motor nn are classically described as entering the EOMs in their middle thirds. We investigated EOM innervation that does not follow the classic pattern.
  
  
  METHODS
  Intact, whole orbits of two humans and one each monkey, cow, and rabbit were paraffin embedded, serially sectioned in coronal plane, and prepared with Masson's trichrome and by choline acetyltransferase (ChAT) immunohistochemistry. Nerves innervating EOMs were traced from the orbital apex toward the scleral insertion, and some were reconstructed in three dimensions.
  
  
  RESULTS
  Classical motor nn positive for ChAT entered rectus and SO EOMs and coursed anteriorly, without usually exhibiting recurrent branches. In every orbit, nonclassical (NC) nn entered each EOM well posterior to classical motor nn. These NC nn entered and arborized in the posterior EOMs, mainly within the orbital layer (OL), but often traveled into the global layer or entered an adjacent EOM. Other NC nn originated in the orbital apex and entered each EOM through its orbital surface, ultimately anastomosing with classical motor nn. Mixed sensory and motor nn interconnected EOM spindles.
  
  
  CONCLUSIONS
  EOMs exhibit a previously undescribed pattern of NC innervation originating in the proximal orbit that partially joins branches of the classical motor nn. This NC innervation appears preferential for the OL, and may have mixed supplemental motor and/or proprioceptive functions, perhaps depending upon species. The origin of the NC innervation is currently unknown.
authors.affiliation: Department of Ophthalmology, University of California-Los Angeles, Jules Stein Eye Institute, 100 Stein Plaza, Los Angeles, CA 90095-7002, USA.
authors.forename: Roberta M
authors.initials: RM
authors.lastname: da Silva Costa
authors.forename: Jennifer
authors.initials: J
authors.lastname: Kung
authors.forename: Vadims
authors.initials: V
authors.lastname: Poukens
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Demer
mesh_terms: D000293:Adolescent; D000818:Animals; D002417:Cattle; D006801:Humans; D008251:Macaca; D008297:Male; D009801:Oculomotor Muscles / Q000294:innervation*; D009802:Oculomotor Nerve / Q000033:anatomy & histology*; D009915:Orbit / Q000033:anatomy & histology*; D011817:Rabbits