Pharynx and Muscles of mastication

Question 1

Pharynx

Answer 1

• Striated muscular tube (has voluntary and involuntary control)
• Lined by mucosa of endodermal origin
• Forms part of the gut

Question 2

Pharynx functions

Answer 2

• Common intersection for passage of both air and food

Question 3

Soft palate of pharynx

Answer 3

In domestic animals, soft palate is elongated past the epiglottis

Question 4

Reason horses are obligate nose breathers

Answer 4

Their soft palate extends so far down that air does not easily pass into trachea from mouth

Question 5

Subdivisions of pharynx

Answer 5

1. Oropharynx
2. Nasopharynx
3. Laryngopharynx

Question 6

Oropharynx

Answer 6

• Extends from the palato -glossal arch (enderside of the end of hard palate) to the base of the epiglottis
• Often connected with tonsils

Question 7

Lymph tissues of the oropharynx

Answer 7

• Tonsils- Shape and position varies among species
• Some diffuse lymphatic tissues are also present

Question 8

Palatine tonsils in dogs and cats

Answer 8

Evaginate into oropharynx lumen and are partly covered by a fold of mucosa

Question 9

Tonsils of ox

Answer 9

Invaginate into pharyngeal walls

Question 10

Tonsils in horses

Answer 10

More diffuse and ventrolateral

Question 11

Tonsils in pigs and horses

Answer 11

• Continue to the dorsal midline
• Named soft palate tonsils

Question 12

Nasopharynx

Answer 12

• 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

Question 13

Auditory tubes when swallowing

Answer 13

• Tubes will open when swallowing or yawning
• At the same time, the intra-pharyngeal ostium will close

Question 14

Laryngopharynx

Answer 14

Extends from the palate-pharyngeal arches (intra-pharyngeal ostium) to the pharyngo-esophageal limen (esophagus entrance)

Question 15

Pharynx and nose breathing

Answer 15

Epiglottis rests on top of the free end of the soft palate

Question 15

Swallowing (deglutition)

Answer 15

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

Question 16

Piriform recesses

Answer 16

• Lateral food channels; part of the laryngopharynx
• Allow passage of small amount of fluid (saliva) to go toward the esophagus, without activating swallowing reflex

Question 17

Muscles of the pharynx

Answer 17

1. Tensor veli palatini- depressed soft palate
2. Levator veli palatini- elevates soft palate
3. Pterygopharyngeus- rostral constrictor
4. Stylopharyngeus – dilator
5. Hyopharyngeus- middle constrictor
6. Thyropharyngeus- middle constrictor
7. Cricopharyngeus- caudal constrictor

Question 18

Temporo-mandibular joint (TMJ)

Answer 18

• 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

Question 19

TMJ in carnivores

Answer 19

TMJ articular and teeth occlusal surfaces are closer, so it has mostly hinge-like movement

Question 20

TMJ in herbivores

Answer 20

• TMJ articular and teeth occlusal surfaces are more apart; wide condylar head and a thicker disk
• Allows for a more lateral/grinding movement

Question 21

Mastication muscles of the dog

Answer 21

• Temporalis
• Masseter
• Digastricus
• Mylohyoideus
• Medial pterygoid
• Lateral pterygoid

Question 22

Temporalis

Answer 22

• Allows for strong hinge-like bite
• Will be larger and stronger for carnivores compared to horses

Question 23

Masseter

Answer 23

• Connects the mandible and maxilla
• Allows for closing of jaw

Question 24

Digastricus

Answer 24

• Two bellies- one for facial expression and the other for chewing
• Only muscle to actively open the jaw

Question 25

Lateral pterygoid

Answer 25

• Smaller and more dorsal
• Helps to close jaw

Question 26

Medial pterygoid

Answer 26

• Larger, more ventral
• Helps to close jaw

Question 27

What must be removed to see the lateral and medial pterygoid?

Answer 27

Must remove the masseter and mandibular ramus

Question 28

Key differences of the mastication muscles of the horse when compared to the dog/carnivore

Answer 28

• 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

Question 29

Pharyngeal diverticulum

Answer 29

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