Craniofacial Muscles

232 M.S. Shall
the medial branch of the hypoglossal nerve (Aldes 1995 ; Kitamura et al. 1985 ;
Uemura-Sumi et al. 1988 ) . In the human, the hypoglossal cranial nerve receives a
contribution from the fi rst cervical nerve for its innervation of the geniohyoid muscle
(Curto et al. 1980 ) . The more dorsal compartment of the hypoglossal nucleus
contributes motoneurons to the lateral branch, which supplies the HG and SG.
McClung and Goldberg ( 1999 ) also found that the superior and inferior longitudinal
muscles are involved in tongue retrusion and are innervated by the motoneurons
located in the dorsal part of the hypoglossal nucleus.
13.4 Somatic Sensation
Tongue sensation is frequently associated only with taste, supplied by cranial nerves
VII, IX, and X. However, somatic sensation of the tongue surface plays a vital role
in both proprioception of the tongue and manipulation of food so that the food bolus
is of an appropriate size for the esophagus and in a position for swallowing. Steele
and Miller ( 2010 ) emphasize in their review that sensory feedback is important to
all phases of deglutination. Anterior tongue sensation triggers the subconscious
pharyngeal swallow. Sensory receptors continue to monitor the bolus as the sequential
motor activity of the tongue moves it along. The esophageal swallow intensity
is modi fi ed in response to the sensory evaluation of the bolus, and secondary peristalsis
is initiated.
The lingual nerve off the mandibular division of cranial nerve V is responsible
for the somatic sensation of the anterior 2/3 of the tongue surface, while branches of
the maxillary division provide input from the palate. The lingual branch of cranial
nerve IX supplies both surface sensation and taste of the posterior 1/3 of the tongue
(Goetz 2007 ) . The internal branch of the superior laryngeal nerve and other branches
of the vagus nerve provide the feedback in the pharyngeal region. Cortically, the
mammalian tongue homunculus is one the largest cortical areas dedicated to sensation,
even at birth, leading the infant to explore everything with its tongue. Sakamoto
et al. ( 2008 ) found that most of the somatosensory processing is located in the primary
somatosensory cortex (SI), Brodmann area 40 and the anterior cingulate cortex
(ACC). A fraction of the tongue SI is primarily activated by the anterolateral
tongue, implying its voluntary activity in speech as well as the initiation of feeding
and drinking. It is interesting that children show symmetric patterns of lingual twopoint
discrimination whereas adults develop an asymmetric pattern (McNutt 2009 ) .
This seems to indicate a maturing of language skills as the child learns to emphasize
particular patterns of speech that are speci fi c to the language and region.
Somatosensation of the posterior parts of the tongue is processed less by SI and
more by Brodmann Area 40 and ACC (Sakamoto et al. 2010a ) . It is known that the
ACC plays an important role in sensory, motor, cognitive, and emotional information
(Sakamoto et al. 2010b ) , and pain processing (Schnitzler and Ploner 2000 ; Vogt
2005 ; Qiu et al. 2006 ) . It follows that posterior tongue sensation is more involved in
the maintenance of the patent airway, vomiting and swallowing functions, and the