4. Pharynx and Muscles of Mastication Flashcards
Pharynx:
-a muscular tube
-forms the first part of the gut
-has striated muscle with voluntary and involuntary control
-lined with mucosa of endodermal origin
Pharynx functions as:
-a common intersection for passage of both air and food
What provides the key to understanding the pharynx?
-the soft palate
*pharynx is quite different in humans
Human pharynx:
-distance between the soft palate and the epiglottis
Domestic animals pharynx:
-soft palate is elongated past the epiglottis
>normal breathing: epiglottis is on top of soft palate
Subdivisions of the pharynx:
- Oropharynx
- Nasopharynx
- Laryngopharynx
Oropharynx location:
-from palato-glossal arch to the base of the epiglottis
Oropharynx:
-contains lymphatic tissue (tonsils)
>shape and position of tonsils vary among species
*in most species, some diffuse lymphatic tissue is also present
Oropharynx in dogs and cats:
-palatine tonsils Evaginate (project) into oropharynx lumen
>partly covered by a fold of mucosa
Oropharynx in ox:
-they Invaginate into pharyngeal walls
Oropharynx in horse:
-palatine tonsils are more diffuse and ventrolateral
Oropharynx in pigs and horses:
-tonsils that continue to the dorsal midline are named “SOFT PALATE TONSILS”
Nasopharynx location:
-from the choanal region (caudal edge of hard palate)
-to the palate-pharyngeal arches (intra-pharyngeal ostium)
Nasopharynx contains:
-the openings of the auditory tubes
*swallow: the air is allowed to go to the other side and balance the pressure on the ear drum
Laryngopharynx location:
-from the palate-pharyngeal arches (intra-pharyngeal ostium)
-to the pharyngo-esophageal limen (esophagus entrance)
Pharynx at work: nose breathing
-epiglottis rests on top of the free end of soft palate
Pharynx at work: swallowing (deglutition)
-voluntary initiation
-mechanical reflex completion
Voluntary initiation: swallowing
-tongue pushes the food bolus to the oropharynx
Mechanical reflex completion: swallowing
-stimulation of the oropharynx triggers the swallowing reflex
Swallowing reflex:
- Soft palate moves up and intra-pharyngeal ostium closes
- Laryngeal opening (glottis closes)
- Hyoid apparatus moves forward
- Epiglottis is pushed back to close the glottis
- Food bolus is shot over epiglottis into dilated laryngopharynx
- Pharyngeal muscles contract in sequence behind the bolus to push it toward the esophagus
Piriform recess (lateral food channels):
-in large animals they are part of the laryngopharynx
-allow passage of small amount of fluid (saliva) to go toward esophagus WITHOU activating swallowing reflex
Muscles of pharynx:
- Pterygopharyngeus
- Hyopharyngeus
- Thyropharyngeus
- Cricopharyngeus
- Stylopharyngeus
Muscles of the soft palate
- Tensor veli palatini
- Levator veli palatini
Rostral constrictor of the pharynx:
-pterygopharyngeus
Middle constrictors of the pharynx:
-hyopharyngeus
-thyropharyngeus
Caudal constrictor of the pharynx:
-cricopharyngeus
Dilator of the pharynx:
-stylopharngeus
Tenses the soft palate:
-tensor veli palatini
Elevates the soft palate:
-levator veli palatini
Temporo-mandibular joint (TMJ):
-made up of condylar process of mandible and mandibular fossa of the temporal bone/zygomatic process
Shape of TMJ:
-differs between carnivores and herbivores
Carnivore TMJ:
-articular and teeth occlusal surfaces are closer
>mostly hinge-like movement (‘ball and socket’)
Herbivores TMJ:
-articular and occlusal surfaces are more apart
-mostly lateral/grinding movement
-wide condylar head
-thicker disc
Mastication muscles of the dog:
-masseter
-digastricus
-temporalis
-mylohyoideus
-medial pterygoid
-lateral pterygoid
Masseter:
-mandible to maxilla
-covers zygomatic arch
Digastricus:
-only muscle that actually opens the jaw
-2 muscle bellies
-chewing and facial expressions
Temporalis:
-temporal fossa underneath it
-very strong bite!
Lateral pterygoid:
-smaller and more dorsal
Pigs have a:
-pharyngeal diverticulum directly dorsal to the esophageal entrance
*need to be careful when oral dosing piglets
Oral dosing piglets:
-should be careful not to insert nozzle tip too far in
>if you do it risks rupturing the diverticulum
-deposit it into the oropharynx
Deposit oral medication into oropharynx of pigs:
-level of a vertical line below the eyes
-diverticulum is at the level of the ears
