Lecture Two Flashcards
Anatomy of the Swallow
Dysphagia
Difficulty in Swallowing
Odynophagia
Pain with swallowing
Deglutition
Swallowing
Bolus
a small rounded mass of a substance, especially of chewed food at the moment of swallowing
Anatomy & Physiology of the Normal Swallow
in Adults
- “Swallowing involves coordination of the sequence of activation and inhibition for more than 25 pairs of muscles in the mouth, pharynx, larynx, and esophagus.”
- Oral cavity, oropharynx and esophagus can be thought of as a series of expanding and contracting chambers, divided by muscular sphincters.
- Propulsion of bolus → positive pressure behind bolus & vacuum/negative
pressure in front of bolus - Healthy individuals simultaneously perform a sequence of sensory and
motoric patterns without much effort or conscious awareness. - Swallowing is accomplished by a complex interaction of striated and
smooth muscle whose sensory and motor components are carried by
multiple cranial nerves.
Four Phases of Deglutition
-Oral preparatory phase
-Oral phase
-Pharyngeal phase
-Esophageal phase
Oral Preparatory Phase
- Primary Function: to prepare solids & liquids for a safe swallow
- Begins when food or liquid enters the mouth
- Involves containing, manipulating and mechanically reducing the consistency
and volume - Chewing (mastication) grinds solid material into a manageable texture
- Achieved by circular and lateral motion of the mandible and tongue
Oral Preparatory Phase: Facial Muscles
Orbicularis oris
- maintains oral competence
- (1st sphincter of swallow system
Buccinator muscle
- Muscle of cheek contracts to keep bolus
from pooling in pockets (sulci)
Both receive neural input from the facial nerve (VII)
Oral Preparatory Phase:
Tongue Muscles
4 Extrinsic Muscles
- Hyoglossus; Styloglossus; Palatoglossus
- Aid in positioning of tongue relative to the oral cavity and pharyngeal structures
- Genioglossus
4 Intrinsic Muscles
- Superior Longitudinal, Inferior Longitudinal, Vertical, Transverse
- Act primarily to alter shape and tone of tongue-along with genioglossus
Oral Preparatory Phase: Neural Input to Tongue (Motor)
Hypoglossal nerve (XII), carries motor nerve fibers that innervate both intrinsic and extrinsic tongue muscles (except for palatoglossus)
A branch of pharyngeal plexus from Vagus nerve (X) sends motor fibers to innervate palatoglossus
Oral Preparatory Phase: Neural Input to Tongue (Sensory)
Mechanoreceptors within/on surface tongue are important for determining bolus size
Sensory info from ant. 2/3 of tongue is carried back to central swallowing control center via lingual branch of Trigeminal (V)
Sensory info from post. 1/3 of tongue carried by glossopharyngeal nerve (IX)
Oral Preparatory Phase: Bolus Formation
Throughout the cyclic sequence, saliva is mixed with the material to lubricate and form a bolus
Musculature of the cheeks prevents pooling
Velum is situated anteriorly and inferiorly to
prevent premature spillage
Oral Preparatory Phase: Chewing
MUSCLES OF MASTICATION:
- Masseter closes the jaw, moves mandible up
- Temporalis moves jaw up, forward or back
- Medial Pterygoids work bilaterally to close jaw
- Lateral pterygoids open, protrudes, side to side movement
- Motor fibers controlling the contraction of these muscles are carried in branches of trigeminal nerve (V)
Oral Preparatory Phase: Liquids
- Tongue cupped at the alveolar ridge, with lateral margins sealed at lateral alveolus
- “Collected” bolus is ready to be transported
posteriorly for the oral and pharyngeal phases
Oral Preparatory Phase: Solids
- Mastication (lateral & rotary)
- Gnashed food falls medially to be repositioned for further breakdown
- Chemical digestion
- Peripheral feedback to protect tongue
Salivation
Controlled by the salivatory nucleus in brainstem
Saliva serves to:
- lubricate & dilute the bolus for swallowing
- maintain oral moisture
- reduce tooth decay
- assist in digestion
- naturally neutralize stomach acid from reflux
Oral Prep -> Oral Phase
Oral Phase is next step in process
Oral Phase
- Initiated when the bolus is propelled posteriorly towards the back of the mouth
- Voluntary: 1 - 1.5 seconds to complete
- Tongue presses the bolus against the hard and soft palate for initiation of a pharyngeal swallow
- Specifically, the tip of the tongue is in contact with the lateral alveolar ridge, which results in a central furrow
- Serves as an incline for the bolus to be propelled posteriorly into the pharynx
Oral Phase: Muscle Involvement
Elevation of palate occurs due to contraction of levator veli palatini muscle
- Receives motor innervation from Vagus (X) via pharyngeal
plexus
- Hyoglossus posterior tongue depression (XII)
- Styloglossus tongue up and back during swallowing
- Palatoglossus raises BOT
- Contraction of orbicularis oris and buccinator muscles prevent pressure from escaping forward, out of the mouth
Oral Phase Requirements
- Labial seal
- Lingual movement & coordination
- Buccal musculature
- Palatal musculature
Oral Phase Continued
Tongue tip + Dorsum → contain & ramp
Posterior tongue → more responsible for
delivering bolus to pharynx
Before (or simultaneous to) the first posterior tongue movement, respiration ceases
- Arytenoid cartilages approximate
- VFs adduct
Respiration & the Swallow
- Protection of airway is paramount
- Respiration & Deglutition → Linked
anatomically (mouth & pharynx) and
neuroanatomically (medulla & brainstem)
*** There is a functional relationship
Swallow Apnea
- Period of airflow inhibition
- During mastication, respiratory patterns are
modified from tidal pattern - Apnea does not occur until bolus is at level of valleculae
- Small exhalation occurs just before apnea
- When tail of bolus passes through the UES (but before the UES is fully closed, but mostly), larynx descends, respiration resume (with exhalation)
- Exhalation + release of subglottal air pressure
- Safety feature
- Audible burst
Exhalation-Swallow-Exhalation pattern
- May change w/ age
- Duration, typically 0.75-1.25 second
- Variables: age & bolus size
- Bigger bolus → longer apnea period
Pharyngeal Phase
- Passage of food through pharynx and into esophagus occurs
- Phase is involuntary
*** begins when pharyngeal swallow is triggered - Bolus enters pharynx
- Hyoid bone continues anterior & superior
movement toward edge of mandible - Larynx tilts under the retracting tongue (airway protection)
- Pharyngeal constrictors (all 3) are active to
sequentially narrow and shorten the pharynx - Peristalsis-like, stripping action of posterior
pharyngeal wall - Aids bolus propulsion
***Upward and forward movement of hyoid
bone is important in applying traction forces on the UES to have maximum opening
- parasympathetic signals from glossopharyngeal nerve CN IX sent to brainstem, relax the UES
- UES pulled open by hyolaryngeal movement
- Bolus tail enters esophagus, UES closes & esophageal peristalsis begins
Beginning of the Pharyngeal Phase
- Sensory receptors in tongue & oropharynx are stimulated
- Send sensory info to brainstem & cortex
- Swallow is triggered when head of bolus passes any point between faucial arches or the point where tongue base crosses lower rim of mandible.
- Young & middle-aged adults @ anterior faucial arches
- Older adults (60+) at the point where tongue base crosses lower rim of mandible.
Pharyngeal Phase: Physiological Events
Several simultaneous physiological events occur:
1) Velopharyngeal Port Closure
2) Tongue base movement/ Pharyngeal Wall action
3) Laryngeal closure
4) Anterior and Superior movement of the hyoid bone & larynx
5) Cricopharyngeus / Upper Esophageal Sphincter (UES) opening
Duration about 1 second
Pharyngeal Phase: Velopharyngeal Closure
levator veli palatini, tensor palatini and palatopharyngeus muscles contract →
to seal the velopharyngeal port and prevent material from entering the nasopharynx and to generate pressure within the pharynx
Pharyngeal Phase: Tongue base movement
- Pressure is generated when the tongue base and pharyngeal wall contact and create a peristaltic wave to drive bolus propulsion
- Pressure generated by tongue base and pharyngeal contractions intensifies as bolus viscosity and volume increases
Pharyngeal Phase: Laryngeal closure
3 laryngeal sphincters to prevent foreign material from entering the trachea and lungs
3 Levels of Airway protection
- True Vocal Folds
- Arytenoid Base of Epiglottis False Vocal Folds
- Epiglottis Aryepiglottic Folds
Pharyngeal Phase: Anterior and Superior movement of the hyoid bone & larynx
via the contraction of the suprahyoid musculature (the anterior belly of the digastric, mylohyoid, geniohyoid, stylohyoid, stylopharyngeus, and the thyrohyoid muscles)
Pharyngeal Phase: Cricopharyngeal / Upper Esophageal Sphincter (UES) opening:
- occurs secondary to hyolaryngeal excursion, due to anterior and superior movement of this region
- UES is the most proximal barrier for pharyngeal and GI reflux and protects the pharynx and airway from gastric contents.
- Synchronization of the UES relaxation with
pharyngeal driving forces is imperative for complete transfer of the ingested bolus into the esophagus
Pharyngeal Transit Time
the total duration of time for the bolus to travel from the point at which the pharyngeal swallow is activated until entry into the UES
Involuntary: .6 to 1.0 seconds to complete
Esophageal Phase
- Requires an ordered pattern of
coordinated activities - Esophageal Transit Time: Time from bolus entering UES & exiting the LES; 8-20 seconds
- Peristalsis: Top of esophagus, sequentially
downward
Overview of Phases of Swallowing
- Oral preparation phase: Place food in mouth, manipulate/ chew food (time varies)
- Oral phase (1-1.5 seconds): Propel bolus posteriorly
- Pharyngeal phase (.6 to 1 second): Transit bolus vertically through pharynx
- Esophageal phase (8-20 seconds): Transit bolus vertically through esophagus
Neurological Control
- Swallowing is dependent on both sensory and motor control
- Afferent neurons (sensory) carry nerve impulses from sensory stimuli towards the central nervous system and brain
- Efferent neurons (motor) carry neural impulses away from the central nervous system and towards muscles to cause movement
- Sensory Input -> drives motor output
- Complex oropharyngeal muscle contraction and relaxation sequence is triggered and controlled by a group of neurons within Reticular Formation of brainstem, specifically the Nucleus Tractus Solitarius (NTS) and Nucleus Ambiguus (NA).
- These neurons are collectively referred to as the Central Pattern Generator (CPG)
Central Pattern Generator (CPG)
CPGs are networks of neurons that can produce repetitive, rhythmic muscle activity in the absence of sensory feedback
Nucleus Tractus Solitarius (NTS)
NTS houses sensory nuclei of:
- CN VII (Facial)
- CN IX (Glossopharyngeal)
- CN X (Vagus)
- Provide peripheral sensory feedback to CPG
- Sensory from tongue (taste), velum, pharynx, larynx, upper GI
- Integrates the cardiovascular system, respiration, taste, swallowing
- Most of CN IX and CN X synapse in the NTS
Nucleus Ambiguus (NA)
NA houses motor nuclei for:
- CN IX (Glossopharyngeal)
- CN X (Vagus)
- CN XII (Hypoglossal
- Important for palatal, pharyngeal, laryngeal, esophageal muscle function
How does the CPG Work?
- Studies have shown that if you electrically stimulate these areas in the brainstem, you can elicit a swallow response
- This means that CPGs can produce muscle activity in the absence of sensory feedback from the structures involved, making it a semi-automatic process
- BUT that swallow will not be fully functional which is why we know we also need some cortical input to have an effective swallow
***The Swallow CPG CAN BE MODULATED
- Continuous sensory feedback from pharynx may influence the neurons of CPG, thus modulating the central program
Areas of the Cortex potentially involved in Swallowing
- Pre-central gyrus / Postcentral gyrus
- Insular cortex
- Anterior cingulate cortex
- Supplementary motor area – premotor
- Frontal operculum
- BA 44, 45 (Broca’s!)
- Cerebellum
- Basal ganglia
Swallow Response
- When the swallow response is initiated, this center causes messages to be sent to glossopharyngeal, vagus, and hypoglossal nerves
- Glossopharyngeal is considered the major nerve for the swallowing center
Six cranial nerves provide innervation for swallowing:
- CN V Trigeminal Nerve
- CN VII Facial Nerve
- CN IX Glossopharygeal Nerve
- CN X Vagus Nerve
- CN XI Spinal Accessory Nerve
- CN XII Hypoglossal Nerve
Trigeminal Nerve (CN V)
Motor Component
- Innervates the muscles involved in chewing
- Innervates the tensor veli palatini muscle
- Assists the glossopharyngeal nerve in raising the larynx and pulling it forward
Sensory Component
- Carries feedback about all kinds of sensation from the anterior 2/3 of the tongue (except taste)
- Also carries sensory information from parts of face, mouth and mandible
Facial Nerve (CN VII)
Motor Components
- Innervates lip muscles including orbicularis oris and zygomaticus
- Contraction during oral preparatory and oral stages prevent food from dribbling out
of the mouth
- Innervates buccinator muscles
- Must remain tense during the oral stage to prevent pocketing in sulci
Sensory Component
- carries information about taste from the anterior 2/3 of the tongue
Glossopharyngeal Nerve (CN IX)
Motor Components
- innervates the 3 salivary glands in the mouth
- saliva mixes with the chewed up food to form a bolus
- Provides some innervation to the upper pharyngeal constrictor muscles, along with the Vagus (X)
- Innervates the stylopharyngeus muscle
- elevates the larynx and pulls it forward during the pharyngeal stage
- aids in the relaxation and opening of UES
Sensory components
- mediates all sensation, including taste, from posterior 1/3 of tongue
- carries sensation from the velum and the superior portion of pharynx
Vagus Nerve (CN X)
Motor Components
- responsible for raising the velum as it innervates the palatoglossus and the
levator veli palatini muscles
- Innervates pharyngeal constrictor muscles (with IX)
- Innervates intrinsic musculature of the larynx
- responsible for vocal fold adduction during the swallow
- innervates the cricopharyngeus muscle
- controls the muscles involved in the esophageal stage of the swallow as well as those that control respiration
Sensory Component
- carries sensory information from the velum and posterior and inferior portions of the pharynx
- mediates sensation in the larynx
Spinal Accessory Nerve (CN XI)
Motor Components
- innervates the palatopharyngeus muscle which depresses the velum and constricts the pharynx
- innervates the muscularis uvula which tenses the velum
- innervates the levator veli palatini (with CN X)
Hypoglossal Nerve (CN XII)
Motor Components
- innervates all extrinsic and intrinsic tongue muscles
** It is strictly a motor nerve
Review of Respiration and Swallowing
- Breathing is always chosen over swallowing
- Initiation of swallow during exhalation
- Apneic period during the swallow
- Return to exhalation
- Patients with dysphagia, dementia, infants may initiate the swallow during the inhalation phase
Older Adults A&P
Mastication patterns → steady
- Dentition
- Less dentition → more chewing required
- With age, ossification of thyroid & cricoid cartilages
- Cervical arthritis
- Can be seen on MBS
- Esophageal transit prolonged
-After 60 years, certain propharyngeal swallow physiology noted:
- Hold bolus at floor of mouth & pick it up with tongue tip as oral stage initiates
- Slightly longer oral phase → leads to a normal delay in pharyngeal trigger
- Increased in residue (oral and pharyngeal)
- Increased penetration into laryngeal vestibule (Normal!)
After 70 years
- Larynx gets lower
- Drops to 7th cervical vertebra
After 80 years, significant differences noted
- Reduced neuromuscular reserve
- Reduced maximal laryngeal and hyoid anterior movement
- No reserve to maintain laryngeal or hyoid elevation after UES opening
- With increased age → reduced UES flexibility
The Range of Normal
Volume
- Bolus volume → greatest systematic change in oropharyngeal swallow
- Small bolus; Nice, sequential pattern
- Big bolus; Simultaneous oral & pharyngeal phases; Later tongue base retraction + pharyngeal wall; move toward each other and make contact when bolus tail reaches tongue base
Viscosity
- As increases → requires increased oral tongue, tongue base, pharyngeal wall activity; Valve function increase in duration
Cup Drinking
- Normally: Sequential, early airway closure, slight laryngeal pre-elevation as cup approaches; Airway closure extended across multiple swallows; Lip Closure maintained; VP closure maintained; UES opens repeatedly
Straw Drinking
- Healthy Way; Intraoral suction
- Unhealthy Way; Sucking with inhalation
Chugging:
- Some can chug without a swallow
- Pull larynx forward, opening the UES volitionally
- Hold breath to close airway
- Volitional control over process
