Craniofacial Muscles

160 L.A. Vinney and N.P. Connor
been identi fi ed as the pharyngeal plexus (Hwang et al. 1948 ) , SLN (Kirchner 1958 ) ,
RLN (Hammond et al. 1997 ) , and the cervical sympathetic chain (Hirano 1969 ) or
combinations of these nerves such as the pharyngeal plexus and RLN (Lund 1965 ;
Mu and Sanders 1998 ; Sasaki et al. 1999 ) . In one study, EMG recordings of the CP
were examined to determine how similar they were to EMG recordings of different
muscles with known innervation (Halum et al. 2006 ) . The authors obtained EMG
recordings for the CP muscle and examined either the ipsilateral inferior constrictor,
TA, or CT muscles simultaneously. The authors’ logic was that if the same nerve
innervated the CP and one or all of these other muscles, then EMG signals in patients
with nerve injury would have common characteristics. EMG test results fell into
one of the following categories: normal, inactive axonal injury, or neurogenic active
axonal injury. The authors found that in 27 out of 28 studies, the ipsilateral inferior
pharyngeal constrictor and CP muscle had the same muscle fi ndings whereas only
40 of 50 studies and 31 of 50 studies were the same between the CP and TA, and CP
and CT, respectively. Based on these fi ndings, the pharyngeal plexus appeared to
predominantly contribute to CP innervation because greater commonality was found
between CP EMG patterns and those of the inferior pharyngeal constrictor, which is
innervated by the pharyngeal plexus (Halum et al. 2006 ) .
Although passive tone is typically always present in the CP, muscular tension
increases as the muscle is stretched (Lang and Shaker 1997 ) . As previously mentioned,
when swallowing occurs, the CP relaxes to allow bolus passage (Lang and
Shaker 1997 ; Plant 1998 ; Kahrilas 1997 ) . While pressure from the bolus contributes
slightly to UES opening, the anterior–posterior movement of the hyoid bone creates
a strong negative pressure that facilitates UES opening and relaxation (Belafsky
2010 ; Plant 1998 ) . The larger the bolus, the more the UES and CP will relax to
widen the UES opening and increase bolus fl ow rates (Plant 1998 ) .
High-resolution manometry (HRM) provides information on pressure changes
during swallowing as well as excellent spatial and temporal resolution. Thus, it has
been used to examine how bolus size and postural changes may in fl uence UES
opening and pressures during deglutition. Durations of UES opening have been
found to vary with different volumes of a liquid bolus based on HRM measures
(Hoffman et al. 2010 ) . Speci fi cally, larger liquid bolus volumes have resulted in
increased UES opening durations (Hoffman et al. 2010 ) . Additionally, examination
of normal swallows via HRM indicated that maximal UES pressure was signi fi cantly
lower in swallows performed in a neutral position vs. those performed with a head
turn. UES pressure was also signi fi cantly higher post swallow with head rotation vs.
neutral positioning. The time that the UES remained open was also greater via head
turn (Fig. 9.8 ).
The CP’s main functions include preventing re fl ux from entering the airway
(Belafsky et al. 2010 ) and preventing passage of air into the esophagus and
abdomen during swallowing (Belafsky et al. 2010 ; Kahrilas 1997 ; Plant 1998 ) .
A healthy CP also allows for quick and ef fi cient swallowing to occur. Thus, when
CP relaxation is delayed or inadequate, the fl ow rate of swallowed materials may
slow and result in residual food materials collecting in the pharynx. The failure of the
CP to relax and allow for the UES to widen has been associated with progressive