Craniofacial Muscles

9 Structure and Function of the Laryngeal and Pharyngeal Muscles
159
Fig. 9.7 Drawing of
cricopharyngeus muscle
showing the muscle’s
horizontal and oblique
compartments known as the
pars obliqua and pars
fundiformis, respectively. CC
cricoid cartilage; CPo
oblique compartment of
cricopharyngeus muscle; Cph
horizontal compartment of
cricopharyngeus muscle; CT
cricothyroid muscle; IPC
inferior pharyngeal
constrictor muscle; T trachea;
TC thyroid cartilage; UE
upper esophagus. Used with
permission from the fi rst
author: Mu and Sanders
( 2002 )
Muscle fi ber properties of the CP muscle have been identi fi ed as predominantly
slow contracting Type I fi bers based on MyHC assays (Davis et al. 2007 ) . When the
CP muscle and the pharyngeal constrictors were compared in human samples, the
CP was found to have muscle fi bers with a smaller cross sectional area, while no
distinct differences in fi ber type composition were observed (Sundman et al. 2004 ) .
In this study, slow muscle fi ber types predominated in the CP and the constrictors,
but across samples in the CP there were fi ndings of hybrid fi bers, on average, (Type
I and Type IIA) 9% of the time and 28% of the time in the pharyngeal constrictors
(Sundman et al. 2004 ) .
As shown in Fig. 9.7 , the CP has two compartments known as the pars oblique
(or simply, oblique) and pars fundiformis (Plant 1998 ) . The pars fundiformis compartment,
also known as the horizontal compartment (Mu and Sanders 2002 ) is
what is typically referred to when the CP is discussed (Plant 1998 ) . The fundiformis
is a sling shaped (Belafsky et al. 2010 ; Belafsky 2010 ) , striated skeletal muscle that
attaches to the posterior aspect of the cricoid cartilage. It is composed of small fi bers
(typically 25–35 m m) that are predominantly Type I to allow for sustained contraction
of the UES (Mu and Sanders 2002 ) .
Innervation of the CP is controversial (Halum et al. 2006 ; Mu and Sanders 1998 ;
Sasaki et al. 1999 ) . The branches of the vagus reportedly innervating the CP have