2. INTRODUCTION
• Swallowing involves the passage of a bolus of food or liquid from
the oral cavity to the stomach via the pharynx and oesophagus,
passing over the entrance to the laryngeal vestibule.
• Partly reflex ; partly under voluntary control.
• Co-ordinated movements.
4. A mid-sagittal section of the head
and neck showing the location of
the major structures involved in
swallowing.
A. Hard palate
B. Soft palate
C. Nasopharynx
D. Pharyngeal isthmus
E. Oropharynx
F. Laryngopharynx
G. Cricoid cartilage
H. Thyroid cartilage
I. Hyoid bone
J. Laryngeal inlet.
6. ORAL PHASE
• PREPARATORY PHASE :
Jaw - closed by the jaw elevators, temporalis, masseter and medial
pterygoid.
Chewing - combination of elevators and depressors of mandible.
Lips maintain a tight seal under the action of the orbicularis oris .
Buccinator is used to return food from the vestibule during the process
of mastication.
Soft palate is lowered under the action of the palatoglossus and
palatopharyngeus which approximate the arches of the same name to the
dorsal aspect of the posterior part of the tongue.
7.
8. TRANSPORT PHASE / ORAL PHASE PROPER
• The tongue is moved by the action of the intrinsic muscles
together with the genioglossus which elevates tongue tip and blade
of the tongue towards the hard palate.
• A pre-requisite for this is mandibular elevation .
• The elevation of the mandible assists the suprahyoid muscles in
raising the hyoid bone.
• The elevation of the floor of the mouth is accompanied by lifting
the tongue under the action of the stylohyoid.
9. • Simultaneously, the tongue is flattened and the bolus is moved
back by these muscles together with the superior longitudinal and
transversus muscles as the tongue fills the oral cavity
• As the bolus reaches the back of the tongue, now deeply grooved,
the soft palate is elevated by the levator and tensor veli palatini to
protect the nasopharynx from the entry of food and closes the
airways.
10. The anterior and lateral views of tongue position in holding bolus immediately before
initiating oral stage of swallow.
12. • The initiation of swallowing involves contact of the food with
the faucial arches or with the mucosa overlying the posterior
pharynx in the region that is innervated by the
glossopharyngeal nerve.
• ‘Trigger point' - summation of afferent signals for the entire
oropharyngeal sensory field.
13. (a) Closure of nasopharynx - Soft palate contracts against the
Passavant’s ridge on the posterior pharyngeal wall and
completely cuts off the nasopharynx from the oropharynx.
(b) Closure of oropharyngeal isthmus - The entry of food back into
oral cavity is prevented by contraction of tongue against the palate
and sphincteric action of palatoglossal muscles.
(c) Closure of larynx - Aspiration into the larynx is prevented
3-Tier system –
1) Closure of laryngeal vestibule by contraction of aryepiglottic &
interarytenoid muscles.
2) Ventricular bands approximation .
3) Adduction of vocal cords by adductors.
14. • During this phase, the glottis is closed by adduction of the
arytenoids and contraction of the lateral cricoarytenoid muscles,
false vocal folds and true vocal folds.
• Epiglottis covers the laryngeal entrance and directs the bolus in
two parts into the valleculae and the pyriform sinuses.
• The two columns of the divided bolus meet at the upper border of
the cricopharyngeus muscle which relaxes to allow the bolus to
enter the oesophagus.
15. • Rapid laryngeal elevation occurs during the pharyngeal phase of
the swallow and appears to be essential for normal swallowing.
• This manoeuvre produces a drop in pressure and transient negative
pressure in the cricopharyngeal sphincter as the bolus passes from
the pharynx into the oesophagus.
16. Neuromuscular Activities Characteristic
of the Pharyngeal Swallow (brainstem)
velopharyngeal closure to prevent backflow of material up the
nose.
tongue base retraction to propel the bolus through the pharynx.
pharyngeal contraction to clear residue through the pharynx.
airway protection, which involves both elevation and closure
of the larynx.
cricopharyngeal or upper esophageal sphincter (UES) opening
to allow the bolus to pass into the esophagus.
17.
18. OESOPHAGEAL PHASE
• After food enters the oesophagus, the cricopharyngeal sphincter
closes and the peristaltic movements of oesophagus take the bolus
down the stomach.
• Gastro-oesophageal sphincter at the lower end of oesophagus
relaxes well before peristaltic wave reaches and permits fluids to
pass.
• Bolus of food is passed by contraction of peristaltic waves and then
the sphincter closes.
19. • The anterior superior movement of the laryngohyoid complex
acts to open the upper oesophageal sphincter.
• The bolus passes through the sphincter and moves along the
oesophagus by peristalsis.
• The levator and tensor veli palatini relax lowering the soft
palate.
• The laryngeal vestibule opens, the hyoid drops and the vocal
cords open.
• This opening of the glottis at the very end of the oropharyngeal
swallow sequence is part of the airway protection mechanism.
20. Esophageal Phase (8-20 sec)
• Primary peristalsis: Sequential contraction of the
circular muscle of the esophageal body, which results
in a contractile wave that migrates toward the
stomach
• Relaxation and opening of the LES
• Involuntary control: Vagus
• Secondary peristalsis: A peristaltic sequence that
occurs in response to distention of the esophagus
(not associated with UES relaxation or deglutition)
21. • Regurgitation of food back from stomach into oesophagus is
prevented by :
tone of gastro-oesophageal sphincter.
negative intrathoracic pressure.
pinch-cock effect of diaphragm.
mucosal folds.
oesophagogastric angle.
slightly positive intra-abdominal pressure
23. Oral and pharyngeal stages of
a normal swallow:
(a) oral phase, food is
reduced and the bolus
prepared
(b) bolus is moved to the
posterior part of the tongue
(c) bolus contacts
the trigger points in the
oropharynx and the
pharyngeal phase is initiated
(d) bolus is moved past the
closed larynx
(e) Bolus enters the
oesophagus.
24. RESPIRATION & SWALLOWING
(SWALLOW APNOEA)
Ventilation has to be suspended during pharyngeal transit of
the bolus.
Typically less than one second in length, corresponding to the
duration of the reflex part of the swallow in its pharyngeal
phase.
The duration of swallow apnoea is dependent upon bolus
volume and possibly bolus consistency.
25. • Swallowing tends to occur during the expiration phase of
respiration.
• Expiration occurs after 80-100 percent of healthy
swallows.This is likely to be a protective mechanism: material
left in the laryngeal vestibule post swallow will be moved to
the pharynx rather than sucked into the lungs.
• There does not seem to be an effect of bolus volume or gender
on the exhale-swallow-exhale pattern.
• The respiratory rhythm is reset after swallowing and there is a
shift in the timing of all subsequent breaths post-swallow: type
I phase resetting.
27. NEURAL CONTROL
• Neural control is divided between the cortex and the brainstem.
• Cortical control of swallowing is bilateral, though one hemisphere
is usually dominant.
• The voluntary initiation of swallowing involves bilateral areas of
the prefrontal, frontal and parietal cortices.
28. • Positron emission tomography (PET) of the cortex following
passive initiation of swallowing reveals activity in several
regions like the face areas of both the primary sensory and
motor cortex, as well as the prefrontal swallowing areas which
are located just anterior to the face region of the precentral
gyrus in the primary motor cortex, corresponding to
Brodman's area 6.
• Stimulation here produces swallowing activity in the
appropriate muscles of the oral cavity, pharynx, palate and
larynx
29. • Afferent input from the jaw, muscles of mastication, lips and
tongue, pharynx, larynx , oesophagus.
To brainstem, cortex
• The efferent pathways (medulla and pons) cranial motor
nuclei muscles of swallowing
nucleus ambiguus for the muscles of the palate, pharynx and
larynx .
hypoglossal nucleus for the muscles of the tongue .
motor nuclei of the trigeminal and facial nerves for the
muscles of the jaws and lips.
• In addition, motor neurones within the cervical spinal cord
control the muscles of the neck including the infrahyoid.
30.
31. Neural Regulation of Swallowing
• Pharyngeal:
– Stimulation of receptors (7th, 9th, and 10 cranial nerves)
– Efferent (motor) function (9th, 10th cranial nerves).
Cricopharyngeal sphincter opening is reflexive
• Esophageal:
– Primary peristalsis
• Proximal- striated- contracts first
• Distal- smooth- contracts later
– Secondary peristalsis
• Intrinsic plexus: Auerback’s myentric plexus
32. Cranial Nerves
• CN V and XII: Chewing & tongue movements.
• CN VII: Sensation of oropharynx & taste to anterior 2/3 of
tongue .
• CN IX: Taste to posterior tongue, sensory and motor functions
of the pharynx.
• CN X:
– Taste to oropharynx, and sensation and motor function to
larynx and laryngopharynx.
– Airway protection
33. • Two main groups of neurones for the coordination and
regulation of swallowing by the medulla.
The first lies in the dorsal region of the medulla above the
nucleus of the solitary tract(lateral medullary swallowing
centre).
Site of convergence of sensory input from the various nuclei and
is probably important in the sequencing of swallowing.
A second group lies more ventrally around the nucleus
ambiguus (medial medullary swallowing centre).
Distributes outputs to the various cranial nerve motor nuclei.
(excitatory to agonist muscles and their synergists , inhibitory to
the corresponding antagonist muscles).
34.
35. • The pharyngeal swallow is mediated in the lower brainstem
(the medulla) in the reticular formation immediately adjacent
to the respiratory center.
• Coordination exists between these two centers because
respiration ceases for a fraction of a second when the airway
closes during the pharyngeal swallow.