Craniofacial Muscles

Chapter 3
Extraocular Muscle Structure and Function
Linda K. McLoon , Christy L. Willoughby , and Francisco H. Andrade
3.1 Introduction
It has become increasingly clear that skeletal muscles are not all the same, but have
signi fi cant differences in terms of embryological development, fi ber type, physiological
properties, metabolic properties, and disease pro fi le. If one thinks about
skeletal muscle as a continuum from the least to most complex, with the leg muscle
soleus at one end, the extraocular muscles (EOMs) would be at the other end. The
combination of its unusual properties compared to other skeletal muscles has
resulted in the suggestion that the EOM represent a distinct allotype (Hoh and
Hughes 1988 ) . The goal of this chapter is to summarize the characteristics of the
EOM that make them so unique amongst skeletal muscles.
3.2 Anatomy
The EOM are traditionally described as including 7 muscles in each orbit. Six muscles
move each eye in the orbit, 4 rectus muscles and 2 oblique muscles, and the location
of each determines its role in controlling eye position and movement. A seventh
L.K. McLoon, Ph.D. (*)
Department of Ophthalmology, University of Minnesota, 2001 6th Street SE,
Minneapolis, MN 55455, USA
e-mail: mcloo001@umn.edu
C.L. Willoughby
Departments of Ophthalmology and Neuroscience ,
University of Minnesota , Minneapolis , MN , USA
F.H. Andrade , Ph.D.
Department of Physiology , University of Kentucky ,
800 Rose Street , Lexington , KY 40536-0298 , USA
L.K. McLoon and F.H. Andrade (eds.), Craniofacial Muscles: A New Framework
for Understanding the Effector Side of Craniofacial Muscle Control,
DOI 10.1007/978-1-4614-4466-4_3, © Springer Science+Business Media New York 2013
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