Craniofacial Muscles

Chapter 8
Masticatory Muscle Response to Neuromuscular
Diseases and Speci fi c Pathologies
Sadie L. Hebert , Christy L. Willoughby , Francisco H. Andrade ,
and Linda K. McLoon
8.1 Introduction
The masticatory muscles are a complex bilateral set of four muscles (masseter,
temporalis, medial and lateral pterygoid muscles) that control movement of the
temporomandibular joint, between the maxillae and the only moveable bone in the
human skull, the mandible. These muscles are capable of fi ne-tuned gradients of
force and movement, as they are required for production of large forces often needed
in crushing of hard food items, and fi ner movements needed for chewing and human
speech production. As with other craniofacial muscles, the masticatory muscles
have unique phenotypes distinct from limb muscle due to their specialized function
and unique developmental origin. Their characteristics include small myo fi ber
cross-sectional area, fi ber-type speci fi c grouping (Eriksson and Thornell 1983 ) , and
a wide range of myosins that allow for a spectrum of force and contraction speeds
(Stål et al. 1994 ; Korfage et al. 2000 ) .
The masticatory muscles’ distinct development makes them susceptible to a host
of developmental anomalies. In contrast with other craniofacial muscles such as the
extraocular muscles and laryngeal muscles, the masticatory muscles are not as
robustly spared in many skeletal muscle diseases, with relatively complete sparing in
only two conditions that have thus far been reported: spinocerebellar ataxia (SCA)
S.L. Hebert , Ph.D. (*) • C.L. Willoughby
Departments of Ophthalmology and Neuroscience , University of Minnesota,
Minneapolis , MN , USA
e-mail: sjhebert@umn.edu
F.H. Andrade , Ph.D.
Department of Physiology , University of Kentucky , 800 Rose Street ,
Lexington , KY 40536-0298 , USA
e-mail: paco.andrade@uky.edu
L.K. McLoon, Ph.D.
Department of Ophthalmology, University of Minnesota, 2001 6th Street SE,
Minneapolis, MN 55455, 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_8, © Springer Science+Business Media New York 2013
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