NEUROPHYSIOLOGY OF SWALLOWING
Stages of Swallowing
Stages of Swallowing
The act of eating, from the moment food is brought to the
mouth and transported to the beginning of the digestive
tract, is a complex and coordinated neurological process.
 The function of the swallowing apparatus is to transport
materials from the oral cavity to the stomach without
allowing entry of substances into the airway.
 Classically, the act of deglutition is described in four
phases:
(1) The oral preparatory phase, when food is
manipulated in the mouth and masticated, if necessary,
to reduce it to a consistency ready for swallow;

Stages of Swallowing
(2) The oral phase of swallow, when the tongue propels food
posteriorly until the swallow response is triggered;
(3) The pharyngeal phase, when the swallow response is
triggered and the bolus is moved through the pharynx;
and
(4) The esophageal phase, when esophageal peristalsis
carries the bolus through the cervical and thoracic
esophagus and into the stomach.
 There are many types of normal swallows depending on
the type and volume of food being swallowed and the
voluntary control exerted over it.
Oral Preparatory Phase



In the unimpaired individual, the oral cavity functions as
a sensory and motor organ affecting changes in the
physical properties of the food bolus to make it swallowsafe.
Movement patterns in the oral preparatory phase of the
swallow vary depending on the viscosity of the material
to be swallowed and the amount of oral manipulation the
individual uses in savoring a particular food.
This is a voluntary phase of variable length depending
upon the texture of the food.
Oral Preparatory Phase
From the time material is placed in the mouth, labial seal is
maintained to ensure that no food or liquid falls from the
mouth.
 The oral cavity is moist, the nostrils are open, the jaws are
closed, and the lips are together but relaxed.
 The larynx and pharynx are at rest and nasal breathing
continues.
 If mastication is required, the tongue positions food on the
teeth.
 The upper and lower teeth meet and crush the material.

Oral Preparatory Phase





The food falls medially toward the tongue, which moves
the material back onto the teeth as the mandible opens.
The cycle is repeated numerous times before forming a
bolus.
During active chewing, the soft palate is not pulled down
and forward and premature spillage is common and
entirely normal.
In addition to the cyclic movement during mastication, the
tongue mixes the food with saliva.
Tension in the buccal musculature closes off the lateral
sulcus and prevents food particles from falling laterally
into the sulcus.
Oral Preparatory Phase
A great deal of sensory information is processed from
sensory receptors throughout the oral cavity, including the
tongue.
 It is likely that information on bolus volume comes from the
shape of the tongue as it surrounds the bolus prior to
swallow.
 After chewing, the tongue pulls the food into a semicohesive bolus.
 If larger volumes of thicker foods are placed in the mouth,
the tongue will subdivide the food after chewing, forming
only part of it into a bolus to be swallowed at one time.

Oral Preparatory Phase


Subsequent “portions” are sequestered on the side of the
mouth for later swallows.
When sufficient chewing occurs and the bolus as been
shaped, one of two normal hold positions occur:
o
o

In the "tipper" hold position, the bolus is held between the
midline of the tongue and the hard palate with the tongue
tip elevated and contacting the anterior alveolar ridge.
In the "dipper" hold position, the bolus is held on the floor of
the mouth in front of the tongue.
The function of the oral preparatory phase is to reduce
food to consistency for swallow and provide pleasure.
Oral Preparatory Phase: Summary
Functional behaviors of the oral prep phase include:
o Labial closure
o Facial tone
o Lateral and rotary jaw movement
o Lateral and rotary tongue movement
o Lingua-velar seal
Innervation is provided by:
o Cranial nerve V - mandibular movement
o Cranial nerve VII - lip shape & facial tone
o Cranial nerve V, X, XI - velar movement
o Cranial nerve XII - tongue shape and position

Oral Phase




The oral phase of swallow is initiated when the tongue
begins posterior movement of the bolus.
If the bolus is held in the dipper position (approx 20%) of
population), the tongue tip moves forward and lifts the bolus
onto the tongue and into the tipper position.
In what has been described as a smooth stripping action, the
midline of the tongue sequentially squeezes the bolus
posteriorly against the hard palate.
The midline of the tongue moves the bolus in an anterior to
posterior rolling action with tongue elevation progressing
sequentially more posteriorly to push the bolus backward.
Oral Phase




The sides and tip of the tongue remain firmly anchored
against the alveolar ridge.
A central groove is formed on the tongue, acting as a ramp
or chute for food to pass through as it moves posteriorly.
The bolus is kept centered on the tongue by the flattening
of the cheeks against the lateral tongue borders and the
narrowing of the faucial pillars as the soft palate is pulled
down and forward to seal off the oral cavity from the
pharynx.
Thicker foods require more pressure to propel them cleanly
and efficiently through the oral cavity.
Oral Phase


Sensory receptors in the
oropharynx and tongue
itself are stimulated and
send sensory information to
the cortex and brainstem.
When the leading edge of
the bolus or "bolus head"
passes any point between
the anterior faucial arches
and the point where the
tongue base crosses the
lower rim of the mandible,
the oral phase of the
swallow is terminated.
Oral Phase: Summary





The function of the oral phase is movement of
food/liquid bolus into the pharynx.
During the oral phase, the tongue seal around bolus
with tip anchored at alveolar ridge;
The midline of tongue is forced upward by actions of
the mylohyoid, geniohyoid, and digastric muscles;
The root of tongue presses against the velum through
action of the styloglossus and hyoglossus muscles; and
The bolus is propelled upward and backward toward
faucial arches .
Oral Phase: Summary
Innervation is provided by:
o Cranial nerve XII - tongue movement
o Cranial nerves V & XII - floor of oral cavity movement
 This stage usually take less than 1 to 1.5 seconds to
complete.

Pharyngeal Stage


The most sensitive area for
triggering the pharyngeal
swallow, an involuntary
process, is not the tonsillar
fauces or that general area,
but the leading edge of the
epiglottis.
The posterior movement of the
bolus is not interrupted.
Pharyngeal Stage



In younger individuals, the triggering of the pharyngeal
swallow occurs at the anterior faucial arches.
In older individuals, it occurs when the tongue base crosses
the lower rim of the mandible.
A number of physiological activities occur as a result of
pharyngeal triggering including:
(1) elevation and retraction of the velum and complete
closure of the velopharyngeal port to prevent material
from entering the nasal cavity.
(2) elevation and anterior movement of the hyoid bone
and larynx;
Pharyngeal Stage
(3) closure of the larynx at all three sphincters, from bottom
to top, the true folds, the laryngeal vestibule, and
epiglottis;
(4) opening of the cricopharyngeus to allow material to pass
from the pharynx into the esophagus;
(5) ramping of the base of the tongue to deliver the bolus to
the pharynx followed by tongue base retraction and
pharyngeal wall contraction to create positive
pharyngeal pressure; and
(6) progressive top to bottom contraction of the pharyngeal
constrictors.
Pharyngeal Stage



Let’s spend a little bit of time understanding some very
important aspects of this pharyngeal phase: laryngeal
elevation, anterior hyoid traction, UES relaxation, and UES
opening.
Laryngeal elevation is the vertical movement of the entire
laryngeal complex above the critical height needed to
achieve closure of the laryngeal vestibule (Cook &
Kahrilas, 1999).
Elevation of the larynx during swallowing plays an
important role in protecting the laryngeal inlet (Fukushima,
Shingai, Kitagawa, Takahashi, Taguchi, Noda, & Yamada,
2003).
Pharyngeal Stage
o
The thyrohyoid (TH)
muscle is the most
important muscle for
laryngeal elevation
and it is thought to
be innervated by
the pharyngeal
branch of the vagus
nerve.
Pharyngeal Stage
Because of different innervation, laryngeal
elevation alone does NOT open the UES.
 It is possible to have elevation of the larynx,
through contraction of the thyrohyoid muscle but
NO movement of the hyoid, therefore NO
opening of the UES.
 Opening of the UES can only be achieved through
anterior movement of the hyoid bone.

Pharyngeal Stage


Anterior hyoid traction is
a forward pulling force
exerted on the larynx
by contraction of the
suprahyoid musculature.
Specifically, contraction of
the anterior belly of the
digastric muscle and the
the geniohyoid muscle pull
the hyoid) up and
forward.
Pharyngeal Stage


Because the only insertion of
the cricopharyngeus is to the
cricoid cartilage of the
larynx, the sphincter muscle
and larynx are obliged to
move in unison in a forward
direction.
This action opens the UES.
Pharyngeal Stage
Like any sphincter, the cricopharyngeus can only contract or
not contract.
 It has to be OPENED by traction, pressure and gravity or a
combination of all.
 During swallowing, in addition to traction, opening of the
UES is highly dependent on bolus size and weight.
 Boluses of 1-5ml may be too small to produce effective
opening of the UES.
 Patients may aspirate on thin small liquid boluses during
videofluoroscopic swallow studies but not while drinking
larger boluses.

Pharyngeal Stage
Another aspect of the
pharyngeal swallow stage is
epiglottic movement.
 As the hyoid bone moves
anteriorly, the lateral
hyoepiglottic ligaments exert
traction preferentially on the
upper third of the epiglottis
bringing it to a position below
horizontal (Vandaele,
Perlman, & Cassell, 1995).

Pharyngeal Stage
UES relaxation and UES opening are separate and
distinct events.
o The recurrent laryngeal nerve provides motor innervation
of the cricopharyngeus, which also has innervation from
the pharyngeal plexus.
o Damage to either or both will affect the relaxation of
the UES as opposed to its opening.
o Clearly, if it does not relax, then the traction forces
required to open it will either not work or will work
poorly.
o UES relaxation occurs during swallowing-associated
laryngeal elevation.
o
Pharyngeal Stage
The UES ceases contraction 0.1 seconds before it is
pulled open by the movement of the hyoid and its
attachments.
o This happens AFTER the larynx starts to rise,
demonstrating that the two events, while related
occur separately, i.e. laryngeal elevation can occur in
the absence of UES opening.
o Clinically, this is a significant point in that impaired
UES opening can result from either impaired traction
on the sphincter or impaired sphincter relaxation.
o Instances of impaired traction can be felt in clinical
assessment and/or evidenced fluoroscopically by
diminished anterior hyoid displacement.
o
Pharyngeal Stage
o
o
o
o
o
Impaired relaxation is only detectable manometrically.
To summarize, laryngeal elevation is needed to move the
entire larynx into a more protected position.
After the larynx starts to rise, the cricopharyngeus stops
contracting—it relaxes.
With laryngeal excursion in an anterior direction, by
anterior hyoid traction, the relaxed UES is pulled opened,
and the epiglottis inverts.
As the larynx lifts, approximately 2 cm in normal adults,
and moves forward, the arytenoid cartilages are also
being brought closer to the base of the tilting epiglottis
facilitating closure of the airway entrance.
Pharyngeal Stage
o
o
o
o
o
As the bolus enters the UES, the pressure of the bolus
widens the opening.
Larger boluses with larger intrabolus pressure result in
wider UES opening (Coo, Dodos, Dantas, Massey, Kern,
Lang, Brasseur & Hogan, 1989).
Both the diameter and duration of deglutitive sphincter
opening increase with increased swallow bolus volumes.
This is one reason that the VFSS may often provide false
positives.
Apparent bolus pooling may result if the bolus size is not
sufficient to open the UES as they do during real meals.
Pharyngeal Stage Timing
o Finally,
pharyngeal transit time, the time taken for the
bolus to move from the point at which the pharyngeal
swallow is triggered through the UES, is normally 1
second or less.
o The bolus moves smoothly and quickly over the base of
the tongue through the pharynx and into the cervical
esophagus.
o Bolus passage through the pharynx depends on
gravity, pharyngeal shortening, and the propulsive
forces of the pharynx.
Pharyngeal Stage Timing
Although the use of the term "peristalsis" is objectionable
to some, this term most closely describes the rapid, orderly,
sequential, moving front of contracting pressure wave that
is generated during a normal pharyngeal swallow.
o Circumferential and vertical dynamics in pharyngeal
swallowing are equally important (Salassa, 1997).
o The sequential circumferential pharyngeal forces are
propulsive, but unequal.
o Anterior-posterior pressures exceed lateral pressures.
o
Pharyngeal Stage Timing
o Vertical
shortening, universal to "peristalsis" throughout the
alimentary tract, is critical to normal effective bolus
transport.
o The major muscles propelling the bolus include the
palatopharyngeus and the stylopharyngeus which act to
shorten the pharynx as the bolus arrives in the pharynx.
o Then, thyrohyoid shortening, laryngo-hyoid elevation, and
the inferior movement of the tongue base contribute to
further pharyngeal shortening.
o The three pharyngeal constrictors move the bolus in a
sequentially downward direction toward the UES.
Pharyngeal Stage: Summary
The pharyngeal swallow response is triggered as the leading
edge of the bolus passes the inferior rim of the mandible,
although in younger persons the response may be triggered
in the area of the faucial arches.
o During the pharyngeal phase, there is
• posterior movement of base of the tongue
• velopharyngeal closure;
• narrowing and shortening of the hypopharynx;
• elevation and anterior movement of the larynx;
• laryngeal closure; and
• relaxation and opening of UES.
o
Pharyngeal Stage: Summary
o
•
•
•
Innervation is provided by:
CNs V, IX, X, XI - velar movement
CNs V, VII, IX, X, XI, XII - pharyngeal, laryngeal movement
CN IX - sensory input
Esophageal Phase
o
o
o
o
The esophageal phase begins as the tail of the bolus
passes through the UES and continues until it passes into the
stomach at the LES.
The larynx lowers, the glottis opens for resumption of
respiration, and the UES contracts sealing off the cervical
esophagus to prevent redirection of the bolus from the
esophagus back into the pharynx.
Food is transported through the esophagus by involuntary
muscular movements called peristalsis.
Normal esophageal transit time varies from 8 to 20
seconds.
Esophageal Phase
o In
the section of the
esophagus lying just
above (7a) and around
the top of the bolus (6),
the circular muscle fibers
contract, constricting the
esophageal wall,
squeezing the bolus
downward.
Esophageal Phase
o Meanwhile,
the longitudinal fibers lying around the bottom
of and just below the bolus also contract shortening this
lower section, pushing the walls outward so it can receive
the bolus.
o These contractions are repeated in a wave that moves
down the esophagus, pushing the food toward the stomach.
o Passage of the bolus is also facilitated by mucous
secretory glands.
Esophageal Phase: Summary
o
o
o
o
o
The esophageal phase begins as the tail of the bolus
passes through the UES.
The UES closes and the airway opens.
Peristalsis moves bolus down esophagus.
LES opens allowing bolus to enter stomach.
Cranial nerve X is involved in both striated and
smooth muscle contraction.