Pharynx and Muscles of mastication Flashcards
Pharynx
- Striated muscular tube (has voluntary and involuntary control)
- Lined by mucosa of endodermal origin
- Forms part of the gut
Pharynx functions
- Common intersection for passage of both air and food
Soft palate of pharynx
In domestic animals, soft palate is elongated past the epiglottis
Reason horses are obligate nose breathers
Their soft palate extends so far down that air does not easily pass into trachea from mouth
Subdivisions of pharynx
- Oropharynx
- Nasopharynx
- Laryngopharynx
Oropharynx
- Extends from the palato -glossal arch (enderside of the end of hard palate) to the base of the epiglottis
- Often connected with tonsils
Lymph tissues of the oropharynx
- Tonsils- Shape and position varies among species
- Some diffuse lymphatic tissues are also present
Palatine tonsils in dogs and cats
Evaginate into oropharynx lumen and are partly covered by a fold of mucosa
Tonsils of ox
Invaginate into pharyngeal walls
Tonsils in horses
More diffuse and ventrolateral
Tonsils in pigs and horses
- Continue to the dorsal midline
- Named soft palate tonsils
Nasopharynx
- Extends from the choanal region (caudal edge of hard palate) to the palato-pharyngeal arches (intra-pharyngeal ostium)
- Contains the openings of the auditory tubes
Auditory tubes when swallowing
- Tubes will open when swallowing or yawning
- At the same time, the intra-pharyngeal ostium will close
Laryngopharynx
Extends from the palate-pharyngeal arches (intra-pharyngeal ostium) to the pharyngo-esophageal limen (esophagus entrance)
Pharynx and nose breathing
Epiglottis rests on top of the free end of the soft palate
Swallowing (deglutition)
Voluntary initiation- tongue pushes the food bolus to the oropharynx
Mechanical reflex completion- stimulation of the oropharynx triggers the swallowing reflex
1. Soft palate moves up and intra-pharyngeal ostium closes
2. Laryngeal opening (glottis) closes
3. Hyoid apparatus moves forward
4. Epiglottis is pushed back to close the glottis
5. Food bolus is shot over the epiglottis into dilated laryngopharynx
6. Pharyngeal muscles contract in sequence behind the bolus to push it toward the esophagus
Piriform recesses
- Lateral food channels; part of the laryngopharynx
- Allow passage of small amount of fluid (saliva) to go toward the esophagus, without activating swallowing reflex
Muscles of the pharynx
- Tensor veli palatini- depressed soft palate
- Levator veli palatini- elevates soft palate
- Pterygopharyngeus- rostral constrictor
- Stylopharyngeus – dilator
- Hyopharyngeus- middle constrictor
- Thyropharyngeus- middle constrictor
- Cricopharyngeus- caudal constrictor
Temporo-mandibular joint (TMJ)
- Made up of the condylar process of mandible and mandibular fossa of the temporal bone/zygomatic process
- Shape of TMJ differs between carnivores and herbivores
TMJ in carnivores
TMJ articular and teeth occlusal surfaces are closer, so it has mostly hinge-like movement
TMJ in herbivores
- TMJ articular and teeth occlusal surfaces are more apart; wide condylar head and a thicker disk
- Allows for a more lateral/grinding movement
Mastication muscles of the dog
- Temporalis
- Masseter
- Digastricus
- Mylohyoideus
- Medial pterygoid
- Lateral pterygoid
Temporalis
- Allows for strong hinge-like bite
- Will be larger and stronger for carnivores compared to horses
Masseter
- Connects the mandible and maxilla
- Allows for closing of jaw
Digastricus
- Two bellies- one for facial expression and the other for chewing
- Only muscle to actively open the jaw
Lateral pterygoid
- Smaller and more dorsal
- Helps to close jaw
Medial pterygoid
- Larger, more ventral
- Helps to close jaw
What must be removed to see the lateral and medial pterygoid?
Must remove the masseter and mandibular ramus
Key differences of the mastication muscles of the horse when compared to the dog/carnivore
- TMJ is much stronger, more complicated. Greater distance between TMJ and occlusal surfaces
- Temporalis is much smaller because side to side chewing more important than hinge
- Digastricus- has 3 bellies which allows for better open and closing of very large jaw
Pharyngeal diverticulum
Medial section of pig head; directly dorsal to the esophageal entrance
- Need to be careful when oral dosing piglets: don’t want to insert nozzle tip too far in which could rupture diverticulum
- Should deposit medication in the oropharynx (vertical line behind the eyes). Away from the diverticulum which is vertical line from the ears
