The Swallow in Detail

The Swallow in Detail

 

Taken from: *Dysphagia Foundation, Theory and Practice by Julie Cicheroand Bruce Murdoch*

 

Hunger

Smell of food, empty stomach or electrolyte imbalance informs hypothalamus of the need to eat.

Brainstemactivates nucleii of CN VII and IX to promote secretion of salivary gland juices to prep for bolus

 

Chewing 

Bolus in mouth.  CN VII ensures good lip seal (orbicularisoris) while CN V relays sensory info to brainstem to constantly modify the fine motor control of bolus prep.

Motor activity to CN V, VII, IX, X, XII to create an enclosed environment within the mouth to prepare the bolus.

Cheeksprovide tone (buccinator CN VII).

Soft palate tense and drawn down towards tongue (tensor velipalatini CN V and palatopharyngeusCN IX)

Tongue is drawn up towards the soft palate (palatopharyngeusCN X, styloglossus CN XII).

Hyoidbone is stabilized (infrahyoid muscles CN XII and C1-C3) to allow movement of the mandible).

Bolus prepared by closing (temporalis, masseter, meial pterygoid,lateral pterygoid, CNV) and opening (mylohyoid and anterior belly of digastric CNV, geniohyoid CNXII &C1-C3.)

Bolus pushed around the mouth by actions of the tongue to create a consistent, homogenous texture (hypoglossus, genioglossus,styloglossus and 4 groups of intrinsic muscles of the tongue CN XII). Taste sensations (CN VII and IX) provide info to cortex to stimulate areas of brain required to coordinate the swallow (insulaand cingulatecortex).

 

Voluntary initiation

Once bolus is adequately prepared.

Soft palate elevates slightly (levator veli palatini and palatopharyngeusCN X).

Slight elevation of hyoid bone (suprahyoid muscles contracting on rigid mandible with slight relaxation of infrahyoid muscles.

Pharyngeal tube is elevated (stylopharyngeus CN IX, palatopharyngeusand salpingopharyngeus CN X).

Tongue delivers bolus to force bolus distally towards posterior wall of the pharynx in a “piston-like” manner using hard palate for resistance. Sensation by CN XI and by CN X (pharyngeal plexus).

 

Larngeal elevation

1st motion for tongue to propel bolus into oropharynx is elevated anterior direction toward roof of mouth (mylohyoid and anterior belly of digastric, CNV; stylohyoid and posterior belly of digastric CNVII; palatoplossusCN X; genioglossus, hyoglossus and styloglossusCN XII; geniohyoid CN XII and C1-C3) affects hyoid elevation in an anterior direction.

Soft palate seals off nasopharynx.

Superior constrictors begin medialization of the lateral walls.

Larynx elevated and moved anteriorly in relation to hyoid bone by thyrohyoid CNX.

 

Laryngeal closure

During laryngeal elevation-vestibule closes and rises relative to thyroid cartilage (cricothyroid and intrinsic laryngeal muscles CN X).

Opposition and elevation of arytenoid cartilages provide “medial curtains” of pyriform recesses (aryeppiglottic folds).

Pressure exerted on base of epiglottis causing it to tip and cover the laryngeal vestibule.

Medial constrictors (CN X) “strip” the pharynx by medialization following on from superior constrictors.

Palatedescends (palatopharyngeus CN X), constrictors “strip” and tongue moves posteriorly (styloglossus CN XII) to close oropharynx.

Once the bolus has reached pharyngeal areas innervated by the internal branch of the superior laryngeal nerve swallow reflexive and cannot be stopped.

Anterior and elevated movement of larynx allows cricopharyngeus to be stretched (UES) and opened.

Inferior constrictor finishes medialization and bolus in esophagus.

 
 

Resting state

CNX

Cricopharyngeus resumes tonic state.

Glotticopens and larynx lowers.

Ifbolus present should cough.

Tongue and hyoid and palate return to resting position.

**Oral phase for liquid boluses should take 1 second and the pharyngeal phase with all consistencies should take 1 second.**The ability to contain a bolus is prognostic.**The swallow is a positive pressure phenomena where the pressure is always on the tail of the bolus.

 
 

Triggering the pharyngeal swallow response:

 

        The bolus stimulates CN IX, X, XI in the medullary reticular formation

        (nucleus tractus solitarius) (NTS).

 

        Incoporates (NTS) input from V, VII, XII

 

        NTS signals motor nuclei in teh nucleus ambiguus to help fire IX, X,

        XI.

 

        Nucleus ambiguus innervates muscles of the velum, pharynx, larynx,

        and upper esophagus (IX, X, XI) producing the pharyngeal swallow

        response.

 

       Strongest ties to the NTS=anterior faucial arches, posterior tongue at

       the lower edge of the mandible, valleculae, pyriform sinuses and

       laryngeal aditus.

 

       The anterior faucial arches have a strong connection between the

       sensory receptors and NTS via afferent fibers of the glossopharyngeal

       nerve (IX) creating a trigger point for younger adults.  (Swallows in

       older adults may trigger lower.)

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