Stages of Swallowing

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Neurophysiology of Swallowing

• Stages of Swallowing

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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

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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.

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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 swallow-safe.
• 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.

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Oral Preparatory Phase

• This is a voluntary phase of variable length
  depending upon the texture of the food.
• 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.

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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.

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Oral Preparatory Phase

• Tension in the buccal musculature closes off the
  lateral sulcus and prevents food particles from
  falling laterally into the sulcus.
• 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
  semi-cohesive bolus.

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Oral Preparatory Phase

• 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.
• 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

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Oral Preparatory Phase

• 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.

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Oral Preparatory Phase Summary

• Functional behaviors of the oral prep phase
  include
•  Labial closure
•  Facial tone
•  Lateral and rotary jaw movement
•  Lateral and rotary tongue movement
•  Lingua-velar seal
• Innervation is provided by
•  Cranial nerve V - mandibular movement
•  Cranial nerve VII - lip shape facial tone
•  Cranial nerve V, X, XI - velar movement
•  Cranial nerve XII - tongue shape and position

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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.

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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.

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Oral Phase

• Thicker foods require more pressure to propel
  them cleanly and efficiently through the oral
  cavity.
• Sensory receptors in the oropharynx and tongue
  itself are stimulated and send sensory
  information to the cortex and brainstem.

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Oral Phase

• 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.
• This stage usually take less than 1 to 1.5
  seconds to complete.

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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 . 

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Oral Phase Summary

• Innervation is provided by
• Cranial nerve XII - tongue movement
• Cranial nerves V XII - floor of oral cavity
  movement

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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.

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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

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Pharyngeal Stage
(1) elevation and retraction of the velum and
complete closure of the velopharyngeal port to
prevent material from entering the nasal cavity.
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Pharyngeal Stage
(2) elevation and anterior movement of the hyoid
bone and larynx (3) closure of the larynx at all
three sphincters, from bottom to top, the true
folds, the laryngeal vestibule, and epiglottis
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Pharyngeal Stage
(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.
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Pharyngeal Stage

• Lets 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).

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Pharyngeal Stage

• 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.

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B. Stages of Swallowing3. Pharyngeal Stage
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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.

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Pharyngeal Stage

• Anterior hyoid traction is a forward pulling
  force exerted on the larynx by contraction of the
  suprahyoid musculature.

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Pharyngeal Stage

• Specifically, contraction of the anterior belly
  of the digastric muscle (1) and the the
  geniohyoid muscle (9) pull the hyoid (b) up and
  forward.

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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.

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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.

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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).

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Pharyngeal Stage

• UES relaxation and UES opening are separate and
  distinct events.
• The recurrent laryngeal nerve provides motor
  innervation of the cricopharyngeus, which also
  has innervation from the pharyngeal plexus.
• Damage to either or both will affect the
  relaxation of the UES as opposed to its opening.
• Clearly, if it does not relax, then the traction
  forces required to open it will either not work
  or will work poorly.

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Pharyngeal Stage

• UES relaxation occurs during swallowing- associate
  d laryngeal elevation.
• The UES ceases contraction 0.1 seconds before it
  is pulled open by the movement of the hyoid and
  its attachments.
• This happens AFTER the larynx starts to rise,
  demonstrating that the two events, while related
  are not inseparable, i.e. laryngeal elevation
  can occur in the absence of UES opening.

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Pharyngeal Stage

• Clinically, this is a significant point in that
  impaired UES opening can result from either
  impaired traction on the sphincter or impaired
  sphincter relaxation.
• Instances of impaired traction can be felt in
  clinical assessment and/or evidenced
  fluoroscopically by diminished anterior hyoid
  displacement.
• Impaired relaxation is only detectable
  manometrically.

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Pharyngeal Stage

• 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 contractingit 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.

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Pharyngeal Stage

• 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.

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Pharyngeal Stage

• Apparent bolus pooling may result if the bolus
  size is not sufficient to open the UES as they
  do during real meals.
• 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.
• The bolus moves smoothly and quickly over the
  base of the tongue through the pharynx and into
  the cervical esophagus.

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Pharyngeal Stage Timing

• Bolus passage through the pharynx depends on
  gravity, pharyngeal shortening, and the
  propulsive forces of the pharynx.
• 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.
• Circumferential and vertical dynamics in
  pharyngeal swallowing are equally important
  (Salassa, 1997).

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Pharyngeal Stage Timing

• The sequential circumferential pharyngeal forces
  are propulsive, but unequal.
• Anterior-posterior pressures exceed lateral
  pressures.
• Vertical shortening, universal to "peristalsis"
  throughout the alimentary tract, is critical to
  normal effective bolus transport.
• Thyrohyoid shortening, laryngo-hyoid elevation,
  and the inferior movement of the tongue base are
  the structures most easily identified in
  pharyngeal shortening.

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Pharyngeal Stage Timing

• The major muscles propelling the bolus include
  the palatopharyngeus and the stylopharyngeus
  which act to shorten the pharynx as the bolus
  arrives.
• The three pharyngeal constrictors move the bolus
  in a sequentially downward direction toward the
  UES.
• Pharyngeal swallow response is triggered at
  leading edge of epiglottis although in younger
  persons the response may be triggered in the area
  of the faucial arches.

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Pharyngeal Stage Summary

• During the pharyngeal phase, there is
•  velopharyngeal closure
• narrowing of hypopharynx and posterior movement
  of base of the tongue
•  elevation and anterior movement of the larynx
• laryngeal closure and relaxation and opening
  of UES.
• 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

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Esophageal Phase

• 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.

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Esophageal Phase

• 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.

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Esophageal Phase

• 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.
• These contractions are repeated in a wave that
  moves down the esophagus, pushing the food toward
  the stomach.
• Passage of the bolus is also facilitated by
  mucous secretory glands.

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Esophageal Phase Summary

• 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.