Oral, Pharyngial and Neural conrol in detail

1. PHYSIOLOGY OF SWALLOWING
PRESENTED BY
Dr. Liju Rajan

2. REFERENCE
Scott Brown otorhinolaringology and Head and Neck
Surgery – 7th
Edition
Cummings ORL-HNS 6th
Edition
Glyton And Hall text book of Physiology

3. Swallowing requires the coordinated activity of muscles in
three regions of the head and neck:
the oral cavity,
The pharynx and larynx, and
the oesophagus.

4. 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
The elevators and depressors of the jaw play a key role in
bolus preparation before the swallow is initiated by grinding
and reducing the food between the teeth.

6. Bolus formation is also a function of the tongue,
the intrinsic muscles of which are mainly
responsible for changing the shape of the tongue
and the extrinsic muscles altering its position in
the mouth.
 The actions of these two groups of muscles are
not independent since changes in shape result in
changes in position and vice versa

7. The actions of the tongue and jaw muscles in bolus formation
are aided by that of the
lips in maintaining a seal,
the buccinator muscle of the cheek in returning food from the
vestibule into the oral cavity and
the soft palate in preventing nasal regurgitation and premature
movement of material into the oropharynx

8. On leaving the oral cavity, food enters the
pharynx, a midline tube approximately 15 cm
long continuous with the oesophagus below and
the nasal cavities above and the larynx which
opens on its anterior wall
a natural division of the pharynx into three
regions:
nasopharynx,
oropharynx and
laryngopharynx,

9. The remainder of the pharynx is composed, like the whole of
the gastrointestinal tract, of four layers:
the outer areolar,
the muscular,
the submucous and
the inner mucous membrane.
The muscular layer is composed of
circular and
longitudinal muscles

10. The circular muscles are arranged as a triad, the superior,
middle and inferior constrictors, with the latter being further
subdivided into a thyropharyngeus and cricopharyngeus part
With the exception of the cricopharyngeus, the constrictor
muscles are paired and attach to a posterior midline raphe. The
cricopharyngeus forms a distinct sphincter at the point where
the laryngopharynx joins the oesophagus. There are two
discrete longitudinal muscles on each side, the
palatopharyngeus and the stylopharyngeus.

12. ORAL PHASE
( Preparatory and Proper)

13. Oral Phase - Preparatory
The oral preparatory phase is where food is readied
for swallowing by reducing and mixing it with saliva
by the muscles of the jaw and oral cavity.
 The jaw is closed by the jaw elevators, temporalis,
masseter and medial pterygoid and chewing uses a
combination of elevators and depressors.

15. The lips maintain a tight seal under the action of the
orbicularis oris
The buccinator is used to return food from the vestibule
during the process of mastication.
Throughout this phase the 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.
The airways remain open. Traditionally, the oral cavity was
thought to be sealed posteriorly though recent work
indicates that this may not always be the case.

17. ORAL PHASE PROPER
The oral phase proper involves several distinct muscle
actions. The tongue is moved by the action of the intrinsic
muscles together with the genioglossus which elevates the
tongue tip and blade of the tongue towards the hard palate.
A prerequisite for this is mandibular elevation and although
the mouth does not have to be completely closed during
swallowing, it is hard to swallow with the mouth more than
a little open
The elevation of the mandible assists the suprahyoid muscles
in raising the hyoid bone.

19. The elevation of the floor of the mouth is accompanied by
lifting the tongue under the action of the stylohyoid.
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 to protect the
nasopharynx from the entry of food and closes the airways.
The soft palate is elevated by the levator and tensor veli
palatini.

21. PHARYNGEAL PHASE

22. Pharyngeal phase
As the bolus is moved back by the tongue to enter the
pharynx, a sequence of events is initiated that ensures that
the airways are protected during bolus transport
Firstly, diaphragmatic contraction is inhibited making
simultaneous breathing and swallowing impossible under
normal circumstances.
At the same time, the soft palate is elevated to ensure a
sphincteric closure of the nasopharynx.
Finally, the vocal cords start to close to protect the airways.

23. 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
Recent work involving simultaneous videofluoroscopy and
endoscopy suggests that the ‘trigger point’ may be the
‘summation of afferent signals for the entire oropharyngeal
sensory field’.

24. bolus enters the oropharynx
touches keytrigger points
a reflex is initiated in which the constrictors relax to dilate the
pharynx
The pharynx and larynx are raised by the longitudinal muscles
The bolus is propelled over the epiglottis by the action of the
constrictors contracting in sequence.
The larynx is then closed by contraction of the muscles of the
laryngeal inlet

25. Bolus material is seen in the valleculae and even the pyriform
sinuses in60 percent of liquid and 76 percent of solid
swallows before the swallow is triggered. This calls into
question the term ‘premature spillage’ as an indicator of
dysphagia
It is often said that once the bolus of food has passed the
palatoglossal and palatopharyngeal arches then swallowing
becomes reflexive. While it is true that swallowing is
automatic once initiated, many people can voluntarily delay
their swallowing up to a certain point

26. The bolus enters the pharyngeal space there is widening of
pharynx and its raised
This is partly due to the relaxation of the pharyngeal
constrictors and partly to the anterior movement of the
pharynx as the hyoid bone is drawn forward under the
elevating action of the suprahyoid muscles.
Laryngeal elevation also occurs as the suprahyoid muscles
move the hyoid bone anteriorly, contributing to pharyngeal
dilation.
 Raising the larynx narrows the laryngeal inlet and moves it
towards the pharyngeal surface of the epiglottis as the
laryngeal cartilages move anteriorly.
The interarytenoid, aryepiglottic and thyroepiglottic muscles
all help to close the margin of the laryngeal aditus in the
manner of a drawstring purse.

29. Pharyngial Phase – Epiglottis
movement
The movement of epiglotis is usually described as occurring
in two distinct stages,with the first bringing the epiglottis
from a vertical to a nearly horizontal position and the second
moving the upper third of the epiglottis to below the
horizontal to cover the narrowed laryngeal aditus.

30. Some authors state that both actions occur passively due to
movements of adjacent structures and forces generated by
compression of the pre-epiglottic adipose fat pad, and within
the ligamentous attachments of the epiglottis, or by a
combination of the two.
Others claim that the second epiglottic movement is
generated actively by the action of the thyroepiglottic and
hyoepiglottic muscles.
 In favour of an entirely passive mechanism, it has been
claimed that these muscles are too sparse to generate
adequate force and that some of their attachments are not
consistent with such an action.

31. Pharyngeal phase - pyriform
sinuses
As the food passes over the posterior part of the curved
epiglottis, it is diverted into the lateral food channels and the
pyriform fossae
Early studies suggested that airway protection was further
maintained by the bolus splitting after passing the base of
tongue, moving laterally through the pyriform sinuses and
rejoining to pass into the oesophagus. Recent evidence has
shown that solids tend to go straight over the epiglottis,
while liquids are diverted laterally.

32. The pharynx constricts behind the bolus as the superior
constrictor muscle contracts. The bolus is carried down the
pharynx by a coordinated peristaltic wave in which the three
constrictor muscles contract in the appropriate sequence.

33. Oesophageal phase
The cricopharyngeus relaxes and 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 ofthe glottis at the very end of the
oropharyngeal swallowsequence is part of the airway
protection mechanism.

35. NEURAL CONTROL

36. NEURAL CONTROL
Neural control of the complex activity of healthy swallowing
involves a number of different regions of the central nervous
system (CNS)
This extends from motor neurons within motor neuclei of
brainstem up to cortex.
The act of swallowing is regulated by sensory feedback
although its importance is only recently found.
The initiation of swallowing can either be as a voluntary act
or a reflex as the result of stimulation of the appropriate
mucosa in the oral cavity

37. Neuronal control - Cortex
The voluntary initiation of swallowing involves bilateral areas
of the prefrontal, frontal and parietal cortices.
These include 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.

39. Neuronal control - Cortex
These studies show that the lower precentral gyrus and
posterior inferior frontal gyrus control the oral phase of
swallowing.
The pharyngeal and oesophageal phases of swallowing are
controlled from more rostromedial regions of the cortex
within the anterior inferior and middle frontal gyri.
In most people, swallowing control is asymmetrical with the
projection from one hemisphere being larger than the other,
independent of handedness.
this explains both the prevalence of swallowing problems
following stroke and the recovery that occurs in most
patients over a period of weeks

41. Other cortical areas that have been implicated in swallowing
include the frontal operculum, orbitofrontal cortex and the
insula.
 The insula lies deep to the lateral fissure and is covered by
the operculae of the frontal, parietal and temporal lobes and
strokes here can induce dysphagia.
 This suggests that cortical control of swallowing is
hierarchical with precentral areas of the cortex being
influenced by deeper and more caudal centres

42. Neuronal control – Brain
Stem
There are important areas within the brainstem necessary for
the control of swallowing and these are located particularly
within the medulla.
Descending pathways project to these medullary swallowing
centres from the frontal swallowing areas within the cortex.
 These probably include pathways in both the dorsolateral
and ventromedial descending systems through the ventral
and lateral corticobulbar tracts.

43. Swallowing is initiated by touch sensation or pressure from
the liquid or food within the posterior part of the oral cavity,
epiglottis or oropharynx.
Thus the nuclei receiving afferent input from these regions,
which include the
nucleus tractus solitarius and
spinal trigeminal nucleus,

44. The efferent pathways from the medulla and pons to the
muscles involved in swallowing involve several cranial motor
nuclei. The most important are the
Nucleus ambiguus for the muscles of the palate, pharynx and
larynx
the hypoglossal nucleus for the muscles of the tongue and
the 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.

48. Between these input and output pathways are interposed two
main groups of neurones that appear to be essential for the
coordination and regulation of swallowing by the medulla.
The first lies in the dorsal region ofthe medulla above the
nucleus of the solitary tract. A second group lies more
ventrally around the nucleus ambiguus
The dorsal group would appear to be the site of convergence
of sensory input from the various nuclei and is probably
important in the sequencing of swallowing.
The ventral group distributes outputs to the various cranial
nerve motor nuclei.

49. RESPIRATION AND
SWALLOWING
There appears to be an individual swallowing respiration
pattern that matures in the teenage years and is remarkably
consistent thereafter
The existence of such an individual pattern may present a
risk for aspiration if it is disturbed. Disease or injury may
upset this delicate balance, whether due to neurological
insult or common otolaryngological conditions such as
posterior laryngitis

50. Aspiration into upper trachea. Reproduced by
permission of the BMJ Publishing

51. Clearly, ventilation has to besuspended during pharyngeal transit
of the bolus .
This is known as the period of swallow apnoea and is 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
RESPIRATION TRACE
SOUND TRACE
Apnoeic
period

52. In a study of 60 people, one of the largest to
date, Hiss et al. reported that increasing the bolus
volume over 15mL corresponded with increased
swallow apnoea.
 The effect of bolus consistency is less clear.
There is evidence to suggest that solids increase
apnoea but sample numbers are too small to be
unequivocal

53. 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.
 Post-swallow inspiration is more common in populations
with impaired swallowing.
 There does not seem to be an effect of bolus volume or
gender on the exhale–swallow–exhale pattern.