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22 CLINICAL MANAGEMENT OF SWALLOWING DISORDERS
Discussion Questions
Study Questions
References
A Look at the Chapter
A thorough understanding of how dysphagia
occurs and how it is treated requires an understanding of the anatomy and physiology of the
swallowing organs. In this chapter, we provide
an overview of the aspects of the anatomy and
physiology of the swallowing systems; it is not
intended to be a comprehensive study of the
head, neck, digestive, and respiratory anatomy
and physiology. That is beyond the scope of a
textbook for swallowing disorders. Rather, a brief
review of the central and peripheral nervous
systems is outlined. Specific knowledge of the
anatomy and physiology with orientation to the
swallowing organs and nerves is also presented.
This chapter also includes an understanding of
the neurological correlates to normal and disordered swallowing with a focus on the respiratory
system’s role in swallowing. Video examples are
included.
INTRODUCTION
Assessment and treatment of swallowing disorders
require an understanding of the anatomy and physiology of the systems and organs of swallowing. As
you read this chapter, consider that once a swallow
is initiated, the muscles, their connections, and their
nerves go into motion. You will see this motion in
some of the video presentations. But first, let’s get
the “lay of the land,” that is, the description and location of the structures that make swallowing happen.
Figure 2–1 presents an overall view of the head and
neck. Below that is a more detailed description of
the larynx. As you can see, the organs of swallowing
are intimately related to speech and voice. Treatment of swallowing disorders may involve all of the
related structures. However, when a patient is diagnosed with a swallowing disorder, priority is always
given to preventing aspiration. Although treatment of swallowing disorders includes many other
aspects of care, such as quality of life and nutrition,
knowing the mechanisms that allow one to swallow normally and why someone may be swallowing
abnormally is the basis for treating the disorders.
In this chapter, a detailed review of the muscles
that govern swallowing is presented. This chapter
also provides a functional review of the structures,
including the nerves involved in swallowing and
their relationships during the act of swallowing. We
begin with a review of the central nervous system
because the commands to coordinate the interaction
of the organs of swallowing originate there.
CENTRAL NERVOUS SYSTEM
The nervous system is broadly divided into the central nervous system (CNS), which consists of the
cerebral hemispheres containing the brain and spinal cord, and the peripheral nervous system (PNS),
which includes the nerves from the brainstem and
spinal cord and certain ganglia outside of the spinal cord. Figure 2–2 shows a midsagittal view of
the CNS. Figure 2–3 shows the midsagittal view
of the brainstem and the location of the nuclei of the
cranial nerves. Swallowing function involves both
the CNS and PNS. The organs of swallowing such as
the tongue or lips may function normally for certain
functions such as speaking but may not function for
swallowing. Within the CNS, 2 major areas manage
swallowing function. The pons in the upper portion
of the brainstem links the brain to the spinal cord
and serves as a “way station” to and from the brain.
The medulla oblongata is part of the brainstem,
located just below the pons in the upper portion of
the brainstem (see Figure 2–2). It is responsible for
involuntary functions such as sneezing, coughing,
eye blinking, and even mood. The other areas of
the brainstem include the cortical and subcortical
regions of the brain that influence voluntary aspects
of swallowing, such as chewing.
2. ANATOMY AND PHYSIOLOGY OF THE SWALLOWING MECHANISM 23
Superior Concha
Middle Concha
Inferior Concha
Pharynx
Hard Palate
Soft Palate
Tongue
Mandible
Mylohyoid Muscle
Hyoid Bone
Esophagus
Epiglottis
Thyroid Cartilage
Vocal Folds
Tracheal Rings
Cuneiform
Cartilage
True
Vocal Folds
Ventricular
Folds
FIGURE 2–1. The overall view of the head and neck.
Esophageal
Sphincter
Piriform fossa
(recess)
Tracheal
Rings
Epiglottis
24 CLINICAL MANAGEMENT OF SWALLOWING DISORDERS
Frontal lobe
Corpus
callosum
Fornix
Interthalamic adhesion
(intermediate mass of thalamus)
Interventricular
Hypothalamus
Pituitary
gland
Pons
Medulla
Oblongata
Thalamus
Choroid plexus
Fourth ventricle
Posterior
commissure
Pineal gland
Corpora
quadrigemina
Cerebral
aqueduct
Cerebellum
Epithalamus
Midbrain
Spinal cord
FIGURE 2–2. A midsagittal view of the central nervous system.
2. ANATOMY AND PHYSIOLOGY OF THE SWALLOWING MECHANISM 25
Mesencephalic
nucleus of
trigeminal nerve
Nucleus of trochlear
(CN IV)
Motor nucleus of
trigeminal nerve
Trigeminal Nerve (CNV)
Principal (partial)
sensory nucleus of
trigeminal nerve
Glossopharyngeal
nerve
Nucleus
ambiguus
Spinal nucleus
of accessory n.
(CN XI)
Nucleus of abducent
(CN VI)
Facial nucleus
(CN VII)
Dorsal vagal nucleus
(CN X)
Hypoglossal nucleus
(CN XII)
Spinal nucleus of
trigeminal n.
CN XI)
FIGURE 2–3. The midsagittal view of the brainstem and the location of the nucleus of the cranial nerves.
26 CLINICAL MANAGEMENT OF SWALLOWING DISORDERS
PERIPHERAL NERVOUS SYSTEM
The PNS is guided by the CNS in its actions and its
integration of the complex act of swallowing. Many
of these same nerves are also pertinent to speech
Trigeminal nerve nuclei
(CN V)
Nucleus of
abducent n.
(CN VI)
production, although as we noted earlier, they may
function differently for different purposes, and their
neural integration varies depending on the activity.
Figure 2–4 shows the cranial nerves of the PNS
from a posterior view. CN V, CN VII, CN IX, and
CN X show both motor and sensory functions. The
Facial n.
CN VII
Facial nucleus
(CN VII)
Nucleus
ambiguus
Dorsal vagal
nucleus
Abducens n.
CN VI
Vestibulocochlear
CN VIII
Glossopharyngeal n.
CN IX
Vagus n.
CN X
Nucleus of
hypoglossal n.
(CN XII)
Motor Sensory
Schematically
Represented
FIGURE 2–4. Cranial nerves, posterior view. On the left side showing the motor nuclei, on the right side showing
the sensory nuclei.
2. ANATOMY AND PHYSIOLOGY OF THE SWALLOWING MECHANISM 27
hypoglossal nerve (CN XII) is solely for motor function. More information about the sensory and motor
functions is presented later in this chapter.
Figure 2–5A shows a detailed lateral view of
the major muscles of the pharynx. Also shown are
the major external muscles of the jaw and mouth.
Figure2–5B shows the details of the pharyngeal
muscles from the base of the tongue to the esophagus and the longitudinal esophageal muscle.
Styloglossus m.
Stylohyoid ligament
Stylopharyngeus m.
Within each phase of swallowing, specific
nerves carry out motor and/or sensory control. The
result is a highly coordinated and interrelated series
of events that pass the food or liquid to the stomach
for digestion. In addition to this chapter, Ludlow
provides an extensive review of the sensory and
motor control mechanisms for voice and swallow-
1
ing.
The key afferent and efferent neural responsibilities are broadly outlined in Table 2–1.
Superior pharyngeal
constrictor m.
Buccinator m.
Orbicularis oris
2
Glossopharyngeal nerve (CN IX)
Vagus nerve (CN X)
Middle pharyngeal constrictor m.
Superior laryngeal nerve:
Inferior pharyngeal
constrictor m.
Cricopharyngeal part
A
FIGURE 2–5. A. Lateral view of the pharyngeal muscles. continues
Esophagus
Cricothyroid m.
Right recurrent
laryngeal nerve
Depressor anguli oris
Hyoglossus m.
Mylohyoid m.
Digastric m. anterior belly
Internal branch
External branch
28 CLINICAL MANAGEMENT OF SWALLOWING DISORDERS
r
Levator veli palatini muscle
Salpingopharyngeus muscle
Aryepiglottic fold
Cuneiform tubercule
Corniculate tubercule
(Transverse and oblique)
arytenoid muscles
Pharyngeal tonsil
Epiglottis
Cartilaginous part of
pharyngotympanic (auditory) tube
Superior pharyngeal
constrictor muscle
Palatopharyngeous muscle
Middle pharyngeal
constrictor muscle
Stylopharyngeus muscle
Inferior pharyngeal constricto
muscle (cut edge)
Internal branch of superior
laryngeal nerve
Posterior cricoarytenoid muscle
Cricoid attachment of
longitudinal esophageal muscle
Circular esophageal muscle
Cricopharyngeus muscle
(part of inferior pharyngeal constrictor)
Longitudinal esophageal muscle
B
FIGURE 2–5. continued B. Detailed view of the pharynx showing the muscles in relation to the esophagus and the
opening to the larynx.
2. ANATOMY AND PHYSIOLOGY OF THE SWALLOWING MECHANISM 29
TABLE 2–1. Contributions of Cranial Nerves to the Oral and Pharyngeal Phases of Deglutition
Structure Afferent Efferent
Lips V2 (maxillary), V3 (lingual) VII
Tongue V3 (lingual) XII
Mandible V3 (mandibular) V (muscles of mastication), VII
Palate V, IX, X IX, X
Buccal region/cheeks V (muscles of mastication), VII
Tongue base IX XII
Epiglottis (lingual surface) IX X
Epiglottis (laryngeal surface) X (internal branch of superior
laryngeal nerve)
Larynx (to level of true vocal
folds)
Larynx (below true vocal folds) X (recurrent laryngeal nerve) X
Pharynx (naso- and oro-) IX X (except for stylopharyngeus,
Pharynx (hypo-) X (internal branch of superior
a
Adapted with permission from Aviv.
X (internal branch of superior
laryngeal nerve)
laryngeal nerve)
2
X
X
which is innervated by IX)
X
a
ANATOMY OF THE SWALLOWING MECHANISM
The anatomy of the swallowing mechanism can generally be divided into 4 major divisions: (1) oral,
(2)pharyngeal, (3) laryngeal, and (4) esophageal.
Table 2–2 provides a general outline of the
functional components of the normal swallowing mechanism.
specific actions take place to hold the food in the
mouth, chew the food, and then pass it through
the oropharynx to the esophagus where it enters
the stomach. It would be a mistake to ignore any
of these areas individually before describing how
they interact, because each may directly or indirectly
lead to swallowing problems and aspiration of foods
or liquids.
The muscles of swallowing extend from the
head down to the esophagus and, at times of regur-
3
Within each of those divisions,
gitation, even to the stomach. Figure 2–6 shows
lateral and partial posterior views of the muscles
of swallowing. Given that they attach to structures
above and below the oral cavity, their attachments
are dependent on normal facial and thoracic structures. Damage from injury (fracture or removal),
disease (cancer), or surgical treatments (causing
paralysis) may render one or more of the muscles
dysfunctional and thus disrupt normal swallowing.
4
Muscles of the Head and Face
(The Muscles of Expression)
Before any liquid or food can be swallowed, it has to
be entered into the mouth. The muscles of the head
and face act as sphincters to close openings such
as the mouth and eyes. These muscles generally act
to move various areas of the skin covering muscles
deeper in the head and face.
30 CLINICAL MANAGEMENT OF SWALLOWING DISORDERS
TABLE 2–2. Functional Components of the Normal
Swallowing Mechanism
A.
Oral Cavity — Responsible for bolus containment
a
and preparation
1. Containment
a. Lips: closure after bolus intake
b. Cheeks: adequate tension to assist in lip closure
2. Bolus Preparation
a. Teeth: mastication
b. Tongue: driving force to initially propel the bolus
c. Gingival and buccal gutters: channel the bolus
d. Soft palate: contact with tongue
B. Oropharynx
1. Oropharyngeal Propulsion Pump
a. Soft palate
b. Lateral pharyngeal walls
c. Base of tongue
2. Velopharyngeal Function
a. Soft palate: elevates as tongue propels
b. Tongue elevation: necessary for propulsion
C. Hypopharynx
1. Muscular Propulsion
a. Pharyngeal constrictors
b. Piriform sinuses
c. Cricopharyngeal function
2. Larynx
a. Closure: glottis, ventricular folds, epiglottis
b. Pharyngeal squeeze
c. Hyoid elevation
D. Esophagus
1. Upper esophageal sphincter opening
2. Primary peristaltic wave
3. Secondary peristaltic wave
a
Adapted from Murry and Carrau.
3(p16)
Incidentally, these are the muscles of facial expression,
sometimes valuable in sensing the expressions of children
reacting to tasty or not-so-tasty foods. These muscles can also
warn someone if they have an unusual experience with food
or liquid or express surprise when something feels aspirated.
2. ANATOMY AND PHYSIOLOGY OF THE SWALLOWING MECHANISM 31
Levator veli palatini muscle
Pterygoid plate
Pterygoid hamulus
Buccinator (cut)
Buccinator crest of mandible
Mandible
Digastric muscle (anterior belly)
Stylohyoid muscle (cut)
Mylohyoid muscle
Thyroid cartilage
Median cricothyroid ligament
Cricothyroid muscle
Cricoid cartilage
Hyoid bone
Trachea
Diagrastric muscle (posterior belly) (cut)
Styloid process
Stylopharyngeus muscle
Superior pharyngeal constrictor muscle
Styloglossus muscle
Stylohyoid ligament
Middle pharyngeal constrictor muscle
Hyoglossus musle
Greater horn of hyoid bone
Superior horn of thyroid cartilage
Thyrohyoid membrane
Inferior pharyneal constrictor muscle
Cricopharygeus muscle
(part of inferior pharyngeal
constrictor)
Esophagus
FIGURE 2–6. Anatomy of the major closing and opening muscles of the upper esophageal sphincter.
Figure 2–7A is an anterior view of the superficial facial muscles. Figure 2–7B shows the lateral
view of these muscles.
Table 2–3 summarizes the important muscles of
the face as they relate to swallowing.
Oral Cavity
The oral cavity is responsible for gathering foods
and liquids and preparing them for transit. The
important aspects include retaining the food or liq-
uid, chewing the food, mixing it with saliva, and
then advancing the bolus to the posterior oral cavity.
As food enters the oral cavity, the buccinators and
orbicularis oris muscles help to seal the lips and
keep the food on the tongue. Posteriorly, the soft
palate lowers and creates a seal to prevent early
leaking or spillage into the oropharynx, an important part of maintaining airway protection.
5
The tongue takes over quickly once food is in the
oral cavity. The tongue is made up of intrinsic muscles and extrinsic muscles that do this work. Specific
motions are activated to coordinate tongue motion.