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DYSPHAGIA ASSESSMENT AND TREATMENT PLANNING: A TEAM APPROACH
Figure 1–2. Extracranial course of the facial nerve.
1. ANATOMY AND PHYSIOLOGY OF DEGLUTITION
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Figure 1–3. Extrinsic musculature of the tongue and course of hypoglossal nerve (XII).
Note the tongue muscles: styloglossus, genioglossus, and hyoglossus and their attachments. Note how the fibers of the genioglossus muscle attach to the inner surface of
the mandible and the anterior surface of the hyoid bone. Note nerve fibers from cervical nerve rootlets that travel with the hypoglossal nerve and travel to the strap muscles
in the neck.
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Figure 1–4. Muscles of the soft palate. Note the fibers of the palatoglossus muscle between the palate and the tongue base. Contraction of
this muscle approximates the soft palate and the tongue base, effectively closing off the back of the oral cavity from the pharynx during oral
bolus preparation and prevents early entrance of the bolus into the pharynx.
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This action of the soft palate against
the tongue base effectively closes off the
back of the oral cavity and prevents the
bolus from escaping prematurely into
the pharynx. The palate and tongue
base constitute the second sphincter in
the swallowing system. With the soft
palate approximating the tongue base,
the nasopharyngeal airway remains
open during the oral preparatory
phase of swallowing and nasal respiration is uninterrupted. Obstruction
of the nose and nasopharynx due to
any cause such as a mass, severe septal deviation, enlarged nasopharyngeal
adenoid tissue, and so on results in dif-
ficulty with the oral preparatory phase
of swallowing due to the requirement
for nasal breathing during this phase
(Figure1–5).
Cranial nerve XII, the hypoglossal
nerve, carries the motor nerve fibers
that innervate both the intrinsic and
extrinsic tongue muscles, except for the
palatoglossus muscles (see Figure 1–3).
Injury to cranial nerve XII (hypoglossal)
can be detected clinically by asking the
patient to protrude the tongue. The side
of injury will not be able to protrude
due to weakness of the musculature
on that side and the tip of the tongue
will point toward the side of injury.
Figure 1–5. Lateral view from videofluoroscopic swallow-
ing study: Preparatory phase. Note bolus in the oral cavity on the superior surface of the tongue. Palate closes
against the tongue base to close posterior oral cavity from
the oropharynx. Respiration is via nasal cavity as the velopharyngeal valve closes off the oral cavity and opens the
posterior nasopharynx.
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DYSPHAGIA ASSESSMENT AND TREATMENT PLANNING: A TEAM APPROACH
Tongue weakness results in difficulty
with bolus positioning during the preparatory phase of swallowing as well
as early spillage of the bolus into the
pharynx due to incompetence of the
posterior oral cavity sphincter.
A branch of the pharyngeal plexus
from the vagus nerve (X) sends motor
fibers to innervate the palatoglossus muscles (Figure 1–6). These fibers
branch from the vagus soon after the
nerve exits the skull base. Injury to
these nerve fibers results from pathol-
ogy at the skull base or intracranially.
Weakness of the palatoglossus muscle
impairs the activity of the posterior oral
cavity sphincter and results in early
escape of the bolus from the oral cavity
into the pharynx before the onset of the
pharyngeal phase of swallowing.
A high density of mechanoreceptors
within and on the surface of the tongue
indicates that the tongue is an important sensory region for determining
the size of the bolus. Sensory information from the anterior two-thirds of the
Figure 1–6. Pharyngeal plexus and vagus nerve branches. Note fibers to the palato-
glossus muscle and to the pharyngeal constrictor muscles.
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tongue is carried back to central swallowing control centers via the lingual
nerve, a branch of the trigeminal nerve
or cranial nerve V (Figure 1–7). Sensory
information from the tongue is critical
to modulation of bolus preparation and
in the coordination of subsequent swallowing of the bolus.
Sensory information from the posterior one third of the tongue is carried
centrally by the glossopharyngeal nerve,
or cranial nerve IX (see Figure 1–6).
Stimulation of the sensory portion of the
glossopharyngeal nerve in the tongue
base elicits the pharyngeal protection
reflex known as the gag reflex.
Mastication, or chewing, of the bolus
involves the masseter muscles, the temporalis muscles, and the medial and
lateral pterygoid muscles to move the
mandible relative to the maxilla. This
muscle group is known collectively as
the muscles of mastication (Figure 1–8).
Motor nerve fibers controlling the contraction of these muscles are carried in
branches of the trigeminal nerve (V)
(see Figure 1–7). Unilateral weakness
of the muscles of mastication results in
asymmetry of jaw opening with swing
of the mandible toward the normal
side. Information regarding the “hardness” of the bolus material is sensed
Figure 1–7. Trigeminal nerve. Note branches that enter the
tongue and carry sensory information from the tongue (lingual nerve). Note branches to muscles of mastication.
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DYSPHAGIA ASSESSMENT AND TREATMENT PLANNING: A TEAM APPROACH
Side view Side view
External
pterygoid
Internal
pterygoid
Geniohyoid
Figure 1–8. Muscles of mastication. From Foundations of Speech and Hearing:
Anatomy and Physiology (p. 167), by Jeannette D. Hoit, Gary Weismer, and Brad Story,
2018, Plural Publishing. © 2018 by Plural Publishing.
Temporalis
Masseter
via muscle spindles in the muscles of
mastication during chewing. This information is relayed to the cerebral central
control mechanisms via the trigeminal
nerve (V).
Salivation
Successful transfer of a food bolus
from the oral cavity into the esophagus
requires the mixing of the bolus with
saliva. Saliva lubricates and dilutes
the bolus to an optimal consistency for
swallowing. Saliva contains two major
types of protein secretion: an enzyme
for digesting starches and mucus for
lubricating purposes. Normal salivary
secretion ranges from 1.0 to 1.5 liters per
day. Saliva also plays an important role
in maintaining healthy oral tissues. It
is bacteriostatic and controls the pathogenic bacteria normally present in the
oral cavity that are largely responsible
for dental caries. The secretion of saliva
is controlled by the salivatory nucleus
in the brainstem. The nerve fibers of the
parasympathetic nervous system carry
signals from the salivatory nucleus to
the salivary glands. The parasympathetic nerve fibers arrive in the oral cavity as part of the lingual nerve, a branch
of the trigeminal nerve (Guyton, 1981)
(Figure 1–7).
ORAL PHASE
The bolus is propelled from the oral
cavity into the pharynx during the
oral phase of swallowing. The top of
the tongue is placed on the superior
alveolar ridge behind the maxillary
central incisors. Voluntary opening of
the pharynx then begins with elevation
of the soft palate and depression of the
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Superior
constrictor
Middle
constrictor
Inferior
constrictor
Figure 1–9. Posterior view of the pharyngeal constric-
tor muscles. The superior pharyngeal constrictor is suspended from the skull base via the pharyngobasilar
fascia. Note the paired muscles meet in the midline.
From Foundations of Speech and Hearing: Anatomy
and Physiology, 2nd ed. (p. 133), by Jeannette D. Hoit,
Gary Weismer, and Brad Story, 2022, Plural Publishing. ©
2022 by Plural Publishing.
11
posterior tongue (see Video 1–1, Straw
www
Drinking on the companion website). In
this way, there is expansion of the posterior oral cavity and a chute forms in
the tongue base guiding the movement
of the bolus into the pharynx. Elevation of the palate occurs as a result of
contraction of the levator veli palatini
muscle (see Figure 1–4). The levator veli
palatini muscle receives motor innervation from the vagus nerve (X) via the
pharyngeal plexus (see Figure 1–6). The
hyoglossus muscle (innervated by XII)
and, to a lesser extent, the styloglossus muscle (also innervated by XII) are
active in posterior tongue depression.
The anterior half of the tongue is then
pressed against the maxillary alveolar ridge and the anterior half of the
hard palate in rapid sequence, moving
the bolus posteriorly on the dorsum
of the tongue. Coordinated and effective tongue movement, full range of
tongue motion, and tongue strength are
imperative for the efficient transfer of
the bolus from the oral cavity into the
pharynx. Tongue muscle weakness, cranial nerve XII injury, or tethering of the
tongue secondary to injury or surgery
can prevent adequate tongue function
and can impair bolus movement into
the pharynx.
Contraction of the orbicularis oris and
buccinator muscles prevents pressure
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DYSPHAGIA ASSESSMENT AND TREATMENT PLANNING: A TEAM APPROACH
escape forward, out of the mouth, or
laterally during bolus movement into
the pharynx. Patients with facial muscle
weakness have difficulty with the oral
phase of swallowing due to the incompetence of the first valve, the lips. Try
a “dry” swallow of saliva with the lips
open for a firsthand experience of the
difficulty created by a failure of the
anterior oral sphincter!
During the oral phase of swallowing,
soft palate elevation allows the bolus
to pass through the tonsillar pillars
and into the oropharynx. Once the soft
palate is fully elevated, it contacts the
adjacent pharyngeal walls in a valving
action that acts to prevent penetration
of the bolus or escape of air pressure
into the nasopharynx. The side walls
of the nasopharynx, consisting of the
superior pharyngeal constrictor muscles, oppose the soft palate to make a
more forceful closure of the nasopharynx. The superior pharyngeal constrictor is suspended from the skull base
via the pharyngobasilar fascia and the
paired muscles meet and attach to one
another in the posterior midline (see
Figure 1–9). The anterior attachments
of the superior pharyngeal constrictor
include the inferior aspect of the pterygoid plates, the buccinator muscle,
and the inner surface of the mandible
(Figure 1–10).
The effective closing of the nasopharynx, along with the cessation of
nasal respiration, is required to prevent pressure or bolus escape into
the nasopharynx and weakening the
forces that drive the bolus inferiorly
into the pharynx. In this way, the soft
palate has a dual sphincteric function
with respect to swallowing. Along with
the tongue base, the soft palate is part
Superior
constrictor
Middle
constrictor
Inferior
constrictor
Figure 1–10. Lateral view of the
pharyngeal constrictor muscles.
Note the anterior attachment of
the superior pharyngeal constrictor to the mandible and posterior
fascia of the buccinator muscle.
The middle constrictor attaches
to the hyoid bone and the inferior constrictor to the thyroid and
cricoid cartilages. From Founda-
tions of Speech and Hearing:
Anatomy and Physiology, 2nd ed.
(p. 133), by Jeannette D. Hoit, Gary
Weismer, and Brad Story, 2022,
Plural Publishing. © 2022 by Plural
Publishing.
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of the sphincter at the posterior part of
the oral cavity that prevents premature
movement of the bolus into the pharynx
during the preparatory phase of swallowing and the soft palate also forms
a sphincter with the superior pharyngeal constrictor muscles between the
nasopharynx and the oropharynx during the oral and pharyngeal phases of
swallowing. Motor nerve fibers from
the vagus nerve (X) via the pharyngeal
plexus innervate the superior pharyngeal constrictor and palatal musculature (see Figure 1–6). Palatal defects
or weakness result in early spillage of
the bolus into the pharynx during the
preparatory phase of swallowing and
reflux of bolus into the nasopharynx
during the oral and pharyngeal phases
of swallowing. Even if bolus movement
is not significantly impacted by palatal
pathology, forces needed for effective
bolus movement are impaired by pressure escape from the active swallowing
chamber (the oropharynx) through the
incompetent sphincter (palate to nasopharyngeal walls) (Figure 1–11).
Toward the end of the preparatory
phase of swallowing, the hyoid bone is
moderately elevated in preparation for
the pharyngeal phase of swallowing.
The anterior displacement of the hyoid
bone pulls open the anterior-posterior
dimension of the pharynx. This expansion of the pharyngeal chamber creates
a vacuum within the oropharynx that
aids in movement of the bolus into the
pharynx. Early hyoid bone elevation
occurs primarily as a result of mylohyoid muscle contraction. The mylohyoid
muscle attaches to the lateral interior
of the mandible and joins the opposite
Figure 1–11. Lateral view from videofluoroscopic swallowing study:
pharyngeal phase. Note elevation of the palate and contact with
the posterior pharyngeal wall.
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