Week 1 - normal swallow Flashcards
What cranial nerves are involved in swallowing? Also say whether motor and/or sensory
Trigeminal (V) Motor and Sensory Facial (VII) Motor and Sensory Glossopharyngeal (IX) Motor and Sensory Vagus (X) Motor and Sensory Accessory (XI) Motor Hypoglossal (XII) Motor
What are the stages of the process of swallowing? (There are four main ones and one other)
Pre-oral anticipatory stage
- Oral preparatory stage
- Oral stage
- Pharyngeal stage
- Oesophageal stage
What happens in the pre-oral anticipatory stage?
It commences prior to food contacting the oral cavity. It includes:
- salivation at the thought or sight of food
- appetite/pleasure/anticipation when about to eat something the person likes
- pre-knowledge of what the food/drink will feel like in the mouth
- knowledge about how to eat/drink particular item e.g. drinking a hot tea in a very different way to a glass of water.
- This stage is more relevant to those with dementia and TBI where cognitive recognition of food is impacted.
What happens in the oral preparatory stage?
How long is the stage?
This stage involves manipulation of food/liquid to form a cohesive bolus for swallowing. Includes:
- mastication (if solid/semi-solid)
- combination of food with saliva
- tasting the food
- forming a bolus of appropriate size and consistency
Duration of stage depends on bolus consistency and volitional control
What is the airway doing during the oral prep stage?
It is open and breathing is predominantly via the nasal airways. Typical adults can breathe but some may have difficulty holding a bolus in the mouth.
What are the key structures involved in the oral prep stage and what do they do?
Include muscles and Cranial nerves
- Lips (orbicularis oris - CNVII) to keep liquid and food in
- Tongue
>anterior 2/3 of tongue critical for
moving food around to form bolus
> all extrinsic (CNXII for geniohyoid & CNV for all others) and intrinsic
(CNXII) muscles involved to move bolus - Teeth and Jaw
> Temporalis, masseter and medial
pterygoid muscles perform mandibular
closure and grinding (CNV)
> Lateral pterygoid and anterior belly of digastric muscles for jaw opening (CNV) - Cheek - Buccinator (CNVII) flattens the cheek to hold bolus in contact with teeth and stop food from falling between teeth and cheek
- Salivary glands…
How does oral prep differ between liquids and solids?
Liquids
- for liquids the base of the tongue is raised and the velum is lowered/draped (down and forward) on the base of the tongue to stop the bolus from slipping back into airway until ready. Also there is no chewing!
Solids
- When eating solids the tongue does not immediately raise at the back as it is busy moving food to molars.
- soft palate remains in resting position away from base of tongue and it is common for food to prematurely spill down into oropharynx.
- Once chewing is complete and bolus is formed the soft palate then comes down and forward to approximate the base of tongue partially sealing the oral cavity from the pharynx
What do the terms tipper and dipper mean?
When people hold a bolus of water in their mouth they either:
- hold fluid in the midline of the tongue/hard palate with the tip of the tongue raised to the alveolar ridge “tippers” - 80%
- hold fluid in floor of mouth in front of the tongue “dippers” - 20%
how big is a fluid bolus usually?
approx 12ml
How does the amount of food/fluid impact on how the bolus is swallowed?
when larger volumes of food/fluid in the oral cavity, the tongue subdivides the amount, either holding some back with the tongue (liquids) or moving some to the side of the mouth for later swallows (solids) - works only part of the mouthful into a bolus
how does the body sense the kind of food in the mouth and what oral prep is needed?
We have mechanical receptors in tongue, teeth, gums and palate which sense:
- mechanical and temperature info (CNV)
- sensory info relating to taste (anterior 2/3 CNVII and posterior 1/3 CNIX glossopharyngeal)
All sensory info relating to taste, temperature, bolus size and need for mastication is sent to the brainstem and integrated in nucleus tractus solitarius (NTS) of medulla (PLUS cortical control – which will impact duration of oral prep needed. Information is passed to Nucleus Ambiguous which connects to motor fibers of V,VII,XI, XII to create pharyngeal swallow (motor) response
Give an overview of what happens in the oral phase and when it starts/ends?
this is a voluntary stage that begins after the bolus is prepared, with the posterior propulsion of the bolus by the tongue into the oropharynx and then into the hypopharynx. This phase ends with the trigger of the swallow
Outline the steps and structures used in the oral phase
bolus is held in mid-central groove of tongue with lateral edges of tongue against hard palate/lateral side of teeth. Lips and buccal muscles contract and velum elevates to close off nasopharynx. The posterior tongue depresses and anterior tongue presses against hard palate - propelling the bolus backwards in a stripping action
what happens in the pharyngeal stage of the swallow?
- tongue base retraction
- velar closure
- hyoid elevates and moves anteriorly, elevating larynx
- closure of true VFs
- closure of the laryngeal entrance (false VFs, arytenoids medialise and tilt anteriorly, epiglottic base thickens as larynx elevates)
- tongue base contact with PPW
- progressive contraction of pharyngeal constrictor muscles from the top down
- cricopharyngeal sphincter opens to allow passage of bolus into oesophagus
what do the tongue base and pharyngeal wall do in the pharyngeal stage?
once bolus has been propelled over base of tongue (oral stage), then (1) tongue base retracts (moving backwards towards PPW) and (2) pharyngeal wall contraction occurs. This creates narrowing and contact in the pharynx behind the tail of the bolus and helps to increase pressure.
Contraction of the lateral and posterior pharyngeal wall occurs in what’s called a stripping wave, moving bolus down towards cricopharyngeal sphincter
What happens to hyoid and larynx in the pharyngeal stage?
- when the bolus is propelled back into the pharynx in the oral stage, the floor of the mouth muscles contract (mylohyoid and anterior belly of digastric - CNV, and the hyoglosus and geniohyoid - CNXII)
- this moves the hyoid superiorly and anteriorly
- motion of the hyoid + contraction of the thyrohyoid elevates larynx by about 2cm
What does hyoid and laryngeal elevation contribute to? (how does it change the pharynx?)
- shortens the pharyngeal space
- airway closure - elevation of larynx causes epiglottis to invert assisting closure of laryngeal vestibule
- forward movement of hyoid contributes to CP opening
What happens during closure of the larynx in the pharyngeal stage?
- begins with start of epiglottic deflection which is triggered by both elevation of larynx and retraction of the base of tongue
- then vocal folds adduct when larynx is 50% elevated
- laryngeal vestibule closes as arytenoids medialize and tilt forward
what actions are involved in the cricopharyngeal opening?
- tension in the sphincter is released (by neurological process)
- superior/anterior movement of larynx helps to pull CP sphincter open
- pressure within and behind bolus widens CP opening as it passes through
- once bolus is passed and larynx descents, CP returns to state of contraction
what factors facilitate bolus transit?
main factors are:
- tongue driving pressure - retraction of tongue against PPW helps to push bolus
- negative pressure differential created by the opening of the cricopharyngeal sphincter helps to draw bolus in
- To a lesser extent, the contraction of the pharyngeal constrictors help but more so they clear any residue from pharynx
where does the oesophageal stage start and finish?
starts at the cricopharyngeal sphincter and ends at the lower oesophageal sphincter
