Mastication, TMJ & Swallowing

• swallowing

  
  

  describe the oesophageal phase of swallowing

  3.1-

  The upper oesophageal phase Sphincter constricts and the bolus passes downwards

  
  

  Peristalsis drives the bolus down the oesophagus

  
  

  3.2-

  The lower oesophageal phase The Sphincter relaxes to allow the bolus to enter the stomach

  
• swallowing

  
  

  describe the pharyngeal phase of swallowing

  The bolus comes into contact with the pharyngeal wall. The larynx is elevated and the muscles propel the bolus towards the oesophagus.

  
  

  - During swallowing both the intrinsic and extrinsic muscle

  of the larynx prevent food or drink entering the glottis.

  
• swallowing

  
  

  describe the buccal phase of swallowing

  Compression of the bolus against the hard palate by the tongue starts the cascade of actions which are involuntary beginning with the raising of the soft palate

  
• swallowing

  
  

  what are the 3 phases of swallowing?

  1. buccal phase

  2. pharyngeal phase

  3. oesophageal phase

  
• swallowing

  
  

  is swallowing voluntary or involuntary?

  Swallowing starts as a voluntary movement but is mostly an involuntarily act
• swallowing

  
  

  describe swallowing

  - As the bolus reaches the oropharynx the soft palate is tensed and raised by the levator muscles

  - At the same time the superior constrictor contracts to close the nasopharynx from the oropharynx and the suprahyoid muscles contract to raise and bring the larynx forward, particularly geniohyoid and the anterior belly of digastric that sit under the tongue, forcing the epiglottis over the laryngeal opening

  - The epiglottis acts to deflect any food and drink into the piriform fossa

  - The middle and inferior constrictors then contract to push the bolus towards the oesophagus whereby, through peristalsis, the bolus is pushed towards the stomach

  - The aryepiglottic and transverse arytenoid muscles contract reducing the size of the laryngeal inlet. The vocal and vestibular folds also close.

  - Finally, once the bolus is through the muscles relax, the hyoid bone and larynx return to their usual position and breathing can resume
• swallowing

  
  

  how long does it take to get the bolus from the oropharynx to the stomach

  about 2 seconds
• bolus formation

  
  

  describe bolus formation


  - Once the food is sufficiently broken up the tongue gathers the food into a bolus and pushes it towards the oral pharynx by raising against the hard palate.

  - At the same time the palatoglossus muscles relax to open the oropharyngeal isthmus.
• bolus formation

  
  

  what is bolus?

  a small rounded mass of a substance, especially of chewed food at the moment of swallowing.
• what does bilateral contraction of the palatoglossus muscles?

  - bilateral contraction of the palatoglossus muscles narrows the oropharyngeal isthmus with the posterior part of the tongue filling the remainder of the gap. This allows breaking to continue while chewing with the mouth closed and prevent food entering the airway

  
• what does the lips do when food is being chewed in the mouth?

  - the lips reduce the likelihood of the food falling out of the mouth. This is achieved by contracting the orbicularis oris muscle
• what does the tongue do when food is being chewed in the mouth?

  - the tongue that moves food towards the molars, while the cheeks stop it being forced into the vestibule
• what happens when food first enters the oral cavity?

  - incisors and canines take on small portions of solid foods into the oral cavity

  - the food is drenched with saliva from the glands that not only moistens but also contains ptyalin that breaks down the carbohydrates

  - food is also broken down by mechanical action by the molars and premolars, as the mandible is opened and closed through muscle action, e.g. buccinators.
• assisting muscles of mastication

  
  

  what do the suprahyoid muscles do during swallowing?

  The suprahyoid muscles (form the floor of the mouth) generally act to raise the hyoid bone and the larynx when the mandible is stabilised.

  
  

  But can also depress the mandible when acting in conjunction with infrahyoid and lateral pterygoid muscles
• assisting muscles of mastication

  
  

  what do the infrahyoid muscles do during swallowing?

  they act to depress the hyoid bone and larynx during swallowing
• assisting muscles of mastication

  
  

  in which direction do the superior and inferior hyoid muscles contract in?

  always contract bilaterally (both sides of the body)
• assisting muscles of mastication

  
  

  what are the superior and inferior hyoid muscles primarily involved in?

  swallowing
• assisting muscles of mastication

  
  

  give two examples of the minor muscles of mastication?

  the superior and inferior hyoid muscles

  
• muscles of mastication

  
  

  what is the shape of the lateral pterygoid muscle?

  almost triangular in shape

  
• muscles of mastication

  
  

  what is the only muscle to lie horizontally?

  the lateral pterygoid muscle

  
• muscles of mastication

  
  

  what are the 3 actions on the mandible of the lateral pterygoid muscle?

  • Protrusion -

  both sides together are prime protractors. Also the horizontal fibres pull the mandible forwards onto the articular disc.

  
  

  • Depression -

  both sides together not only pull the mandible forwards but depress when combined with the hyoid muscles

  
  

  • Contralateral excursion -

  one side moves the mandible in the opposite direction
• muscles of mastication

  
  

  what are the 3 actions on the mandible of the medial pterygoid muscle?

  • Elevation -

  acting together, the medial pterygoid plus masseter are

  powerful elevators

  
  

  • Protrusion -

  together the right and left muscles aid in protruding the jaw

  
  

  • Contralateral excursion -

  the medial pterygoid from one side moves the jaw to the opposite side
• muscles of mastication

  
  

  what muscle is the mesial pterygoid muscle a mirror of?

  the masseter muscle on the inner surface of the mandible

  
• muscles of mastication

  
  

  what needs to be done so that the medial and lateral pterygoid muscles can be seen?

  the mandible has to be removed

  
• muscles of mastication

  
  

  what fossa do the medial and lateral pterygoid muscles occupy?

  the infratemporal fossa

  
• muscles of mastication

  
  

  what are the 4 actions of the Temporalis muscle?

  • Resting tonus -

  this muscle maintains a normal mandibular rest position when the subject is in the upright position

  
  

  • Elevation -

  e.g. biting uses the fibres of both sides

  
  

  • Retrusion -

  this involves the posterior horizontal fibres of both sides retruding a protruded mandible

  
  

  • Ipsilateral excursion -

  using only one side the temporalis is capable of pulling the mandible to the same side.
• muscles of mastication

  
  

  what are the two heads that the Temporalis muscle arises from?


  - the temporal bone

  - the temporal fascia

  
• muscles of mastication

  
  

  exactly which parts of the side of the skull does the Temporalis muscle originate from?

  1. Superior temporal line

  2. Inferior temporal line

  3. Temporalis fascia

  4. Zygomatic arch

  5. Frontal process of zygoma

  6. Frontal bone

  
• muscles of mastication

  
  

  where does the Temporalis muscle originate from and insert on?

  - Originates from the side of the skull

  - Inserts at the coronoid process of the mandible

  
• muscles of mastication

  
  

  what is the shape of the Temporalis muscle?


  fan shaped

  
• muscles of mastication

  
  

  what are the 3 actions of the Masseter muscle?

  • Elevation -

  uses both masseter muscles, enabling the teeth to be clenched

  
  

  • Retrusion -

  uses the superficial fibres of both masseter muscles, retruding a protruded mandible

  
  

  • Ipsilateral excursion -

  a single masseter can move the mandible to the same side
• muscles of mastication

  
  

  how does the Masseter muscles superficial and deep fibres run?

  - superficial fibres run obliquely (at an angle)

  - deep fibres run almost vertically

  
• muscles of mastication

  
  

  where does the Masseter muscle originate from and insert on?

  - Originates from the zygomatic bone/arch

  - Inserts on anterior border and angle of ramus of mandible

  
• muscles of mastication

  
  

  what shape is the Masseter muscle?

  quadrilateral in shape

  
• muscles of mastication

  
  

  what are the 4 major muscles of mastication?

  - Masseter

  - Temporalis

  - Medial Pterygoid

  - Lateral Pterygoid

  
• Neurovasculature of the muscles of mastication

  
  

  what nerve innervates the muscles of mastication?

  the anterior trunk of the mandibular nerve

  
• Neurovasculature of the muscles of mastication

  
  

  where does the pterygoid venous plexus lie?

  between the temporalis and pterygoid muscles and anastomoses with the facial vein plus the cavernous sinus

  -The facial vein then drains into the internal jugula

  
• Neurovasculature of the muscles of mastication

  
  

  what is the pterygoid venous plexus of veins equivalent to?

  the maxillary artery

  
• Neurovasculature of the muscles of mastication

  
  

  what is the drainage of the muscles of mastication called?

  pterygoid venous plexus

  
• Neurovasculature of the muscles of mastication

  
  

  what is the maxillary artery subdivided into?

  (it is not branched)

  - mandibular

  - pterygoid

  - pterygopalatine