Craniofacial Muscles

46 L.K. McLoon et al.
3.9 Summary
In summary, many unique characteristics set the EOM apart from non-cranial skeletal
muscles. These differences start with the early genetic signaling that controls EOM
formation from the non-segmented cranial mesoderm and continue with the maintenance
of EOM-speci fi c characteristics by up-regulated expression of speci fi c
groups of neurotrophic factors compared to limb muscles. The EOM are continuously
active, even in primary gaze. This constancy in the maintenance of contractile
force must play a role in the molecular and anatomical individuality of the EOM.
The suggestion that the EOM may indeed be a distinct allotype is supported by the
myriad differences between the EOM and non-cranial skeletal muscle, including
the complexity of co-expression patterns of myosin heavy chain isoforms and other
contractile elements, the differences in metabolic pathways used by the EOM, and
their ability to remodel throughout life. These properties play a critical role in determining
the unique functional capabilities of these muscles physiologically (see Das
2012 , Chap. 4 ) as well as their propensity for and sparing from various skeletal
muscle diseases (see Pedrosa-Domellöf 2012 , Chap. 5 ). The ability to control the
direction of gaze, coordinate eye movements with position of the head and body in
space, and follow and track moving objects is critical to being able to navigate in the
world. This complexity must be needed to ensure that we maintain exquisite control
over eye position and eye movements in three-dimensional space.
Acknowledgements Supported by NIH grant EY015313, the Minnesota Lions and Lionessess,
and an unrestricted grant to the Department of Ophthalmology from Research to Prevent
Blindness Inc.
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