The Normal Swallow Flashcards
List the cranial nerves involved in swallowing
- Trigeminal
- Facial
- Glossopharyngeal
- Vagus
- Accessory
- Hypoglossal
List how CNV is involved in swallowing
Sensory: from nasal mucosa, tongue (excluding taste), teeth, gums, palate, lip, cheek + proprioception of muscles of mastication
Motor: Main role – control of muscles of mastication, but also tenses velum, assists glossopharyngeal (IX) to elevate larynx
List how CNVII is involved in swallowing
Sensory: tastebuds on anterior 2/3 tongue, nasal and palatal sensation + proprioception of muscles of facial expression
Motor: muscles of facial expression, secretion of saliva (submandibular, sublingual)
List how CNIX is involved in swallowing
Sensory: tastebuds posterior 1/3 tongue, sensation from pharynx + proprioception of muscles of pharynx
Motor: pharyngeal constriction (with CNX), elevation and anterior movement of larynx, secretion of saliva (from parotid gland)
List how CNX is involved in swallowing
Sensory: from tastebuds on rear of tongue + proprioception of velum pharynx and larynx
Motor: raises velum, contraction of pharyngeal constrictors & VF adduction for laryngeal closure. Innervation of CP muscle, controls oesophageal stage and muscles of respiration
Which of the cranial nerves involved in swallowing have only motor components?
Also discuss what these motor components are
- Accessory (XI)
Tenses and raises velum with CN X, depresses velum, constricts pharynx + muscles for movement of H&N - Hypoglossal (XII)
Motor control of intrinsic and extrinsic muscles of tongue & infrahyoid muscle
List the basic neurological process of swallowing
- Cortical Involvement
Memory, emotion, visual/tactile recognition
Motor and sensory cortex involvement - Food processed and activates sensory receptor
Sensory information from mouth to other structures - Complex neural network to generate a swallow response
Information passes through neural networks to create motor response
Compare the (simple) stages of swallowing with the more complex stages of swallowing.
Simple:
- oral prep + oral phase
- pharyngeal phase
- oesophageal phase
Complex:
- pre-oral anticipatory stage
- oral preparatory stage
- oral stage
- pharyngeal stage
- oesophageal stage
Describe the pre-oral anticipatory stage
Commences prior to food contacting oral cavity
Pre-oral motor, cognitive psychological and somaesthetic elements involved in meal time
Appetite, pleasure, knowledge of taste, temperature
Describe the oral preparatory stage
- Manipulation of food or liquid to form cohesive bolus for swallowing
- Mastication of food and saliva
- Airway is open - through nasal airway
Describe the oral preparatory stage for liquids
- Momentary containment of liquid bolus by the tongue
- Base of tongue is raised
- Velum lowers to base of tongue
Tippers: fluid held in midline of tongue and hard palate with tongue tip elevated and contact alveolar ridge
Dippers: fluid held in floor of mouth in front of tongue
Describe the oral preparatory stage for solids
- Tongue moves bolus laterally to molar ridges
- Crushing movement masticates bolus
- Chewing reflex + stimulates release of saliva from parotid, submandibular and sublingual salivary glands
- Soft palate is in normal resting position (premature spillage is normal/common)
- Once no active chewing soft palate is pulled down and forward to partially seals off the oral cavity from pharynx
What sensory feedback is provided from the oral prep stage?
Information received from mechanical receptors in tongue, teeth, gums, palate
- Mechanical + temp sensory CN V
- Sensory CNVII, CNIX
All information (taste, temperature, bolus size) is sent to brainstem - and impacts duration of oral prep needed
Describe the oral stage
- Voluntary stage
- 1-1.5 seconds in duration
- Begins after bolus is prepared with the posterior propulsion of the bolus by tongue into oropharynx - hypopharynx
- Ends with ‘trigger’ of swallow
- Bolus is held in mid-central depression, with lateral edges of tongue against the hard palate/lateral sides of teeth
- Lips and buccal muscles contract
- Velum elevates to close off nasopharynx
- Posterior of tongue depresses
- Anterior of tongue presses against hard palate and propels bolus backward (stripping action
Compare the oral stage for liquids vs. solids
Liquids:
- less pressure to propel into pharynx
Solids:
- thicker fluids require increased pressure of tongue against
What structures are involved in the oral stage (intrinsic and extrinsic)?1
- intrinsic muscles of tongue to hold bolus
- extrinsic muscles of tongue to propel bolus, and elevate hyoid
What is the pharyngeal stripping wave?
- assists bolus transport
- clearance through pharynx
Describe the commencement of the pharyngeal stage
The pharyngeal stage is rapid <1 second
- Commencement of the pharyngeal stage was once thought to be when the bolus passed the anterior faucial arch, but now more often recognized as:-
On VFSS - The swallow should be triggered by the time the bolus head reaches the point where the tongue base crosses the mandible
FEES view – often triggered when bolus begins pass around epiglottis/ reaches the lateral channels
When/where is the swallow is triggered?
What exactly triggers the swallow, and the extent to which it is under voluntary or reflexive control is not fully understood
But we do know:
- We can volitionally initiate a swallow
- But we do need a bolus (try 4 dry swallows in a row – unable to do once saliva is depleted!)
- And just a bolus in the mouth doesn’t do it
- And just “stimulating” (no bolus) the sensory receptors in the region when the swallow is initiated usually doesn’t initiate a swallow
- Current thoughts – both reflex and voluntary components involved
What do we know about swallowing?
Swallowing initiation is reliant on sensory information mechanical, chemical and water-respondent receptors at various areas including:
- base of anterior facial arch (majority & purported primary area of input), tongue base, uvula, pharynx, epiglottis & pyriform fossae
- These sensory receptors in oropharynx & tongue identify the posterior propulsion of the bolus (particularly deep proprioceptors) and send sensory information via the sensory branch of the superior laryngeal nerve of CNX (Vagus) to the nucleus tractus soltarius where it is decoded and sent to the nucleus ambiguous which initiates the pharyngeal swallow motor pattern
What happens when the pharyngeal stage is triggered?
- Tongue base retraction
- Velar closure – achieved by palatopharyngeal muscle (CNX) & paired levator velar palatini (CN X & XI)
- Hyoid elevates and moves anteriorly, elevating the larynx
- Closure of the true vocal folds
- Closure of the laryngeal entrance (false vocal folds adduct; arytenoids medialize and tilt anteriorly; epilogttic base thickens as larynx elevates)
- Tongue base contact with anterior bulging of posterior pharyngeal wall
- Deflection of the epiglottis over laryngeal entrance
- Progressive contraction of pharyngeal constrictor muscles -top down (pharyngeal stripping wave)
- Cricopharyngeal (CP) sphincter opens to allow passage of bolus into oesophagus
Describe what nasopharyngeal protection is, including when it occurs?
- the end of the oral stage
Patterns of velopharyngeal closure vary, however typically involve:
- Elevation and retraction of soft palate
Inward (anterior) movement of the posterior and lateral pharyngeal walls
- Prevents food/fluid entering nasal vault
-With tongue sealing the bolus and propelling it posteriorly, a closed velopharynx enables build up of pressure in pharynx
What does tongue and pharyngeal wall do?
Once the bolus has been propelled over the depressed base of tongue (at end of oral stage), then (1) tongue base retracts and (2) pharyngeal wall contraction occurs
* Tongue base to PPW should be complete behind the tail of the bolus. This helps to increased pressure in the pharynx
* Contraction of the lateral and posterior pharyngeal
walls occurs in a pharyngeal contraction “stripping” wave (not “peristalsis” as its not a tube!) continuing in a downward direction to the UES
What happens with elevation and anterior movement of hyoid + larynx?
In the action of propelling the bolus back to the pharynx in the oral stage, the floor of mouth muscles contract (mylohyoid + anterior belly of digastric - both innervated by CNV + the hyoglosus & geniohyoid – both CNXII hypoglossal)
This moves the hyoid superiorly and anteriorly
Motion of the hyoid + contraction of the thyrohyoid elevates larynx. Average elevation is approx 2 cm
Hyoid and laryngeal elevation contributes to:
- Shortening the pharyngeal space
- Airway closure – elevation of the larynx causes the epiglottis to invert + creates thickening of base of epiglottis assisting closure of laryngeal vestibule
- The forward movement of hyoid contributes to CP opening
What happens during closure of the larynx?
Begins with start of epiglottic deflection
- Epiglottic deflection is assisted by both the elevation of the larynx and retraction of the base of tongue
Then closure at level of vocal folds. Vocal folds adduct (occurs when larynx is about 50% elevated)
Closure of laryngeal vestibule:
- Arytenoids medialize and move forward narrowing laryngeal opening
- The elevation of the larynx causes thickening of base of epiglottis, assisting closure of vestibule
Hyoid and Laryngeal elevation + contraction of intrinsic laryngeal muscles causes inversion of the epiglottis
When does the upper oesophageal/cricopharyngeal sphincter open?
A series of actions:
- tension in the sphincter is released
- superior and anterior movement of the larynx pulls open the CP sphincter (direct relationship found between amount of hyoid movement and CP opening)
- Superior movement of the larynx assisted by the long muscles of the pharynx – stylopharyngeus, salpingopharyngeus & palatopharyngeus
- Anterior movement of the larynx – effect of digastric muscle elevating the hyoid and the thyrohyoid contracting
- Pressure within bolus and driving bolus widens the CP opening as it passes through
- Once bolus is passed and larynx descends, CP returns to state of contraction
What facilitates bolus transit?
Main Factors:
- tongue driving pressures
the negative pressure differential created by the opening of the cricopharyngeal sphincter
To a lesser extent:
- Contraction of the pharyngeal constrictors. Research suggests that pharyngeal constriction functions more as a clearing force than a driving force.
What is meant by pressure, pumps and seals?
Travelling from mouth to oesophagus:
- Closure of lips & tension of buccal musculature
- Posterior propulsion of the bolus into pharynx by the tongue
- Closure of velopharyngeal port + elevation of the larynx, shortening pharyngeal space
- Closure of true and false vocal folds + opening of cricopharyngeal sphincter opening creates a pressure
differential, which helps to direct the bolus through the
pharynx and into the oesophagus - Pressure to the tail of the bolus caused by the base of
tongue to posterior pharyngeal wall contact + ongoing
downward wave of pharyngeal contraction
What is the pattern of bolus flow?
As the bolus is propelled from the oral cavity it passes over the depressed base of tongue – in a ramp like fashion
At the point of the epiglottis/valleculae, the bolus is diverted around the larynx (not over it). At this point in 80% of ‘normals’, a liquid bolus typically divides in half at the valleculae and then travels down the pharynx in the pyriform sinuses
Solid doesn’t split – goes down 1 side
The bolus then joins together again at the point of the oesophagus
Explain the oesophageal stage
This stage commences with bolus moves through cricopharyngeal sphincter and into the oesophagus and terminates when bolus reaches the lower oesophageal sphincter at opening of the stomach
The bolus is transported by peristaltic waves (yes, this part IS a tube!) which push bolus down to, and through, lower oesophageal sphincter and into stomach
Oesophagus about 23-25cm long. Bolus typically takes between 8-20 seconds to transit
What are some of the other important components of the oesophageal stage?
- swallow respiratory co-ordination
- normal taste
- normal swallow
- flavour perception
Explain the co-ordination of respiration and swallowing?
- Finely tuned co-ordination
- Inhalation on presentation of food
- Swallows predominantly occur in the expiratory phase of respiration
- The period of swallowing apnea is approx 0.3 – 2.5 seconds
- Then this apnea is followed by further expiration 95% of the time
What is considered normal taste?
Perceived by taste buds located on surface of tongue and structures in oropharynx
- Original 4 basic tastes (salty, sour, sweet, bitter) + new 5th taste “Umami”
- Combinations make all possible tastes
- Taste information carried on facial, glossophageal and vagus nerves
hypogeusia: Impaired taste (gustation)
What is considered normal smell?
Smell achieved through
Orthonasal olfaction:
Nasal inhalation allowing molecules to pass to olfactory receptors in epithelium in nasal vault
Retronasal olfaction:
- Odorants diffuse from oral cavity through posterior nasal entrance up to olfactory epithelium (when chewing/expiratory breathing)
- Retronasal olfaction most important in flavor perception while eating
hyposmia, anosmia: Impaired smell (olfaction)
How do we perceive flavour?
Smell + Taste + Chemosensis (texture + temperature) = FLAVOUR
Chemosensis (trigeminal sensations):
- Physical (texture, temperature) and
- Sensory (carbonation, “heat” of chilli, “cold” in menthol)
But of these, SMELL + TASTE contribute most to flavour perception
The of these two, SMELL takes precedent over TASTE in flavour identification
Thought to be about 70% of flavour perception comes from smell
