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Learning Objectives
Anatomy, Physiology and
Neural Control of Swallowing
• Determine relevant anatomical structures to the process of
swallowing
• Describe the stages of swallowing and the corresponding neurological
structures that are involved in the process
• Differentiate the infant and adult human structures of deglutition
Kerwyn Jim C. Chan, CSP-PASP
SP-DYS 336
(Adapted from the lecture of Ms. Carmela Carandang, January 2021)
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Swallowing
• Deglutition
• transitive verb “To take through the mouth and esophagus into the
stomach” (Merriam Webster, 2021) https://www.merriamwebster.com/dictionary/swallow
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Activity 1
• Grab any food or drink that you have
• Take a few bites from your food or a few sips from your drink
• Answer the following questions:
• What parts are involved when you are eating/drinking?
• How did the structures move when you were chewing and/or swallowing?
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Human Swallow: 3 Stage Model
•
O ral Phase
•
Pharyngeal Phase
•
Esophageal Phase
Physiology of Normal Deglutition
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4 Stage Model
Phase 1: Oral Preparatory Phase
• Stage 1: Transport
• Oral Preparatory Phase
• Oral Propulsive Phase
• Pharyngeal Phase
• Esophageal Phase
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• Food is brought into the mouth
• Tongue places and holds the food on the
occlusal surface of lower teeth for food
processing
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Oral Preparatory Stage
Phase 2: Oral Propulsion
Phase
• Food Processing
• Stage 2 Transport
• Immediate follows stage 1 transport
• Mastication and salivation
• Tongue and soft palate movement coordinated
with jaw movement
• Hyoid bone movement
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• Tongue tip rises
• Expands the tongue-palate contact to
squeeze the bolus along the palate and
into the pharynx
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Phase 3: Pharyngeal
Phase
Phase 4: Esophageal
Phase
2 crucial biological features:
1. Food passage, i.e., propelling food bolus
through the pharynx and the UES to the
esophagus
2. Airway protection, insulating the larynx
and trachea from the pharynx during food
passage to prevent the food from entering
the airway
• Upper esophageal sphincter opening and
closing
• Peristaltic wave and gravity moves the bolus
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• Lower esophageal sphincter prevents
regurgitation
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Activity 2
In summary,
• Grab any food or drink that you have
• Take a few bites from your food or a few sips from your drink
• Describe the four phases of swallowing
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Sections
Stage
Oral vestibule
Oral Phase (Preparatory and Propulsive)
Oral cavity
Anatomy and Neuroanatomy of
Normal Deglutition
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Sections
Pharynx
Pharyngeal Phase
Larynx
Esophagus
Esophageal Phase
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Oral Cavity: Vestibule
Oral Cavity: Teeth
• Upper teeth
• Lower teeth
• Types
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Oral Cavity
Oral Cavity: Tongue and Salivary Glands
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Pharyngeal Cavity
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Pharyngeal Cavity: Pharynx
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Pharyngeal Cavity: Larynx
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Pharyngeal Cavity: Vocal Folds
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Esophagus
Nerves Involved in Swallowing
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Nerves in Swallowing
Cranial Nerve V
• CN V: Trigeminal
• CN VII: Facial
• CN IX: Glossopharyngeal
• CN X: Vagus
• CN XII: Hypoglossal
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Cranial Nerve VII
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Hypoglossal nerve (XII)
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Cranial nerves IX, X, XI
• Two groups of lingual muscles
• Intrinsic – originate and insert within the tongue
• Extrinsic – originate outside the tongue and insert within the substance of the
tongue
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Oral Stage
Possible problems in oral
preparatory stage?
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Pharyngeal Stage
Possible deficits in the oral stage?
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Pharyngeal Stage
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Pharyngeal Stage
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Esophageal Phase
• Upper esophageal sphincter
• Lower esophageal sphincter
Possible deficits in pharyngeal
stage?
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Central Pattern Generator
Nerves and Muscles they Innervate
Cranial Nerve
Muscles
V
Masticatory muscles
Mylohyoid
Tensor veli palatini
Anterior belly of digastrics
VII
Facial muscle
Stylohyoid
Posterior belly of digastrics
IX
Stylopharyngeus
X
Levator veli palatini
Palatopharyngeus
Salpingopharyngeus
Intrinsic laryngeal muscles
Cricopharyngeus
Pharyngeal constrictors
XII
Intrinsic tongue muscles
Hyoglossus
Geniohyoid
Genioglossus
Styloglossus
Thyrohyoid
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• Types of movements (Hooper, 2000)
• Reflexes - involuntary, stereotyped, and graded without threshold (e.g. knee
jerk)
• Fixed action patterns - involuntary and sterotyped but typically have a
stimulus threshold (e.g. sneezing)
• Directed movements - voluntary and complex, but neither stereotyped nor
repetitive (e.g. reaching)
• Rhythmic motor patterns - stereotyped, complex, and subjected to voluntary
control (e.g. breathing, walking, swallowing) governed by CPGs
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Swallowing CPG
Swallowing CPG
• DSG
• Composed of interneuronal network with both
afferent and efferent control over swallowing
• Located in two main brainstem areas:
• Involved in triggering, shaping, and timing of the
sequential or rhythmic swallow pattern
• VSG
• Dorsal Swallowing Group (DSG) around the NTS
• Ventral Swallowing Group (VSG) in the ventrolateral
medulla above the nucleus ambiguous (NA)
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• Composed of premotor neurons that excite motor
neuron pools bilaterally
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Swallowing CPG
Swallowing CPG
• Consists of two hemi-CPGs located on each side of
the medulla
• Synchronizes and organizes the bilateral contraction of
muscles during swallowing to improve shaping and
timing of swallows
• Nerve fibers crossing the midline serve as connections
for the hemi-CPGs
• Motor sequence is generated in the ipsilateral CPG
then transfers signals to the contralateral CPG
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Medullary Infarct
Swallowing CPG
• Peripheral afferent inputs
• From oropharyngeal sensory receptors
• Important in initiation of swallowing
• Provides continuous sensory feedback to modify and
modulate the swallowing CPGs
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Swallowing CPG
• Supramedullary inputs
• All afferent fibers involved in initiation or facilitation of
swallowing converge and terminate in the NTS
• Provides inhibition-excitation inputs which result in
sequential activation and inhibition of swallowing
muscles
• Proximal parts of the swallowing tract are activated,
while more distal parts are inhibited
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Swallowing CPG
Swallowing CPG
• Motor outputs
• Controls both reflexive and voluntary swallowing
• Cortical areas control the pharyngeal phase through
the swallowing CPGs
• Involved in protective reflexes such as coughing
• Structures in the swallowing CPG are also involved in
respiration, mastication, and phonation
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Cerebral Cortex
Cerebral Cortex
• Appears to have an asymmetrical representation
of swallowing muscles in the two hemispheres
• Involved in voluntary swallowing which activates
CPGs
• Represented in the lateral precentral and
premotor cortices
• Primary motor cortex (BA 4)
• Premotor cortex (BA 6), supplementary motor
areas, anterior cingulate cortex, insula
• Somatosensory cortex (BA 3,1,2), temporal lobe,
basal ganglia, thalamus, cerebellum
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• Damage to the dominant hemisphere predisposes and
individual to develop dysphagia
• Recovery is associated with an enlargement cortical
representation in the undamaged hemisphere
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Coordination among eating, swallowing and
breathing
Importance of Sensation in Swallowing
• Swallowing is dominant to respiration
• Appropriate preparation of food = continuous feedback of sensory
information from receptors
• Physical closure of airway
• Neural suppression of respiration (brainstem)
• Detects size and texture of the bolus
• Determines the chewing action required from the muscles of mastication
• Pharyngeal phase = sensory input from the posterior oral regions and
pharynx = intensity of pharyngeal muscle activity and overall duration
of the pharyngeal phase of swallowing varies in response to sensory
information relayed from afferent receptors about the unique
characteristics of the bolus
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Difference Between Child and Adult Swallow
Summary:
• Oral Preparatory and Oral Phase – volitional transfer of ingested
material – controlled by the discrete areas of the cerebral cortex; CN
V, VII, IX, XII
• Pharyngeal Phase: swallowing center in the medulla; CN IX, X, XI
• Esophageal Phase: begins following closure of the upper esophageal
sphincter; reflexive component serves the primary function of
transporting food to the stomach by a sequential peristaltic
contraction of muscles initiated in the pharynx and relaxation of the
lower esophageal sphincter; CN X
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References:
• Logemann, J. (1988). Evaluation and treatment of swallowing disorders (2nd ed). Austin, Texas:
PRO-ED
• Mankekar, G. (2015). Swallowing – physiology, disorders, diagnosis and therapy. Mumbai India:
Springer India
• Matsuo, K & Palmer, J. (2008). Anatomy and physiology of feeding and swallowing – normal and
abnormal. NIH Public Access Physical Medicine and Rehabilitation Clinics of North America, 19,
691-707
• Mistry, S. & Hamdy, S. (2008). Neural control of feeding and swallowing. Elsevier Saunders
Physical Medicine and Rehabilitation Clinics of North America, 19, 708, 728
• Ertekin, C. & Aydogdu, I. (2003). Neurophysiology of swallowing. Clinical Neuropsychology 114,
2226-2244
• Swallowing Disorders (Dysphagia) in Adults. Retrieved from:
https://www.asha.org/public/speech/swallowing/Swallowing-Disorders-in-Adults/ Accessed Jan
2021
• Swallow definition. Retrieved from: https://www.merriam-webster.com/dictionary/swallow
Accessed Aug 2021
Questions?
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