Oral Biology: Muscles of Mastication Flashcards
What does “mastication” mean?
Chewing
What does the breakdown of food stuffs via mastication involve? (3)
1) preparation for swallowing
2) increase surface area for chemical digestion
3) release of chemicals for sense of taste
What is stimulated by mastication?
salivary flow
Where do masticatory movements take place?
The temporomandibular joint (TMJ)
What does the TMJ comprise of?
1) Glenoid Fossa of the Temporal Bone
2) Articular Eminence
3) Condyle of the Mandible
What movement occurs at the TMJ with a slight jaw opening?
A simple hinge movement
What movement occurs at the TMJ with a wide jaw opening?
Hinge and Slide
What movement occurs at the TMJ when the jaw protrudes?
Slide movement
What three groups of muscles are involved in mastication?
1) Muscles between the skull and mandible
2) muscles between mandible and hyoid
3) hyoid stabilisers
What group of muscles acts across the TMJ and is considered the main group of muscles of mastication?
Muscles between the skull and the mandible
Name the four muscles under the “Skull-Mandible” group
1) Masseter
2) Temporalis
3) Medial Pterygoid
4) Lateral Pterygoid
What is the:
1) origin
2) insertion
of the SUPERFICIAL MASSETER?
1) Origin: zygomatic arch/bone
2) Insertion: angle/ramus of the mandible
What is the action of the superficial masseter muscle?
Jaw elevation (closing), minor protrusive action
What nerve innervates the superficial masseter?
Masseteric nerve of the Motor Root of CNVc
What is the:
1) origin
2) insertion
of the DEEP MASSETER?
1) Origin: Inner aspect of the zygomatic arch
2) Insertion: angle/ramus of the mandible
What is the action of the deep masseter muscle?
Jaw elevation (closing)
What is the innervation of the deep masseter muscle?
Masseteric nerve of the motor root of CNVc
What is the:
1) origin
2) insertion
of the TEMPORALIS?
1) Origin: inferior temporal line and fascia
2) Insertion: coronoid process
What is the action of the Temporalis muscle?
Jaw elevation and retrusion (due to it’s posterior fibres)
What innervates the Temporalis muscle?
Deep Temporal Nerve of the Motor Root of CNVc
What is the:
1) origin
2) insertion
of the UPPER HEAD of the LATERAL PTERYGOID?
1) Origin: Infratemporal surface of the greater wing of sphenoid
2) Insertion: capsule and articular disc of TMJ
What is the:
1) origin
2) insertion
of the LOWER HEAD of the LATERAL PTERYGOID?
1) Origin: lateral aspect of the lateral pterygoid plate
2) Insertion: pterygoid fovea below head of condyle
What is the action of the lateral pterygoid?
A complex action which ultimately leads to jaw opening.
Initial opening: hinge in lower joint space with help from suprahyoids only.
Wide opening: anterior and inferior translation of condyle assisted by inferior lateral pterygoids
What innervates the lateral pterygoid?
CNVc motor root - nerve to lateral pterygoid
What does the inferior head of the lateral pterygoid do:
1) bilaterally?
2) unilaterally?
Bilaterally:
1) pulls condyle forward
2) assists opening
3) protrusion
Unilaterally:
1) facilitates lateral excursion
When is the superior head of the lateral pterygoid active?
During retrusion and closing
What is the:
1) origin
2) insertion
of the MEDIAL PTERYGOID?
1) Origin: medial aspect of lateral pterygoid plate of the sphenoid bone and maxillary tuberosity
1) Insertion: Medial aspect of ramus/angle of the mandible
What is the action of the medial pterygoid? (2)
1) jaw elevation
2) assists protrusion and lateral excursions (unilateral)
What innervates the medial pterygoid muscle?
CNVc Motor Root - nerve to medial pterygoid
What are the three muscles that fall under the Mandible-Hyoid group?
1) Geniohyoid
2) Mylohyoid
3) Digastric (anterior)
What is the:
1) origin
2) insertion
of the geniohyoid muscle?
1) Origin: inferior mental spine and inferior genial tubercle
2) Insertion: Hyoid bone
What is the action of the geniohyoid muscle when:
1) the hyoid is fixed
2) the hyoid is not fixed
1) hyoid fixed: jaw opening (and retrusion)
2) hyoid not fixed: raise (and forward) hyoid
What innervates the geniohyoid muscle?
C1 spinal nerve (with hypoglossal)
What is the:
1) origin
2) insertion
of the MYLOHYOID muscle?
1) Origin: mylohyoid line of the mandible
2) upper border of the hyoid bone
What innervates the mylohyoid muscle?
CNVc Motor Root - nerve to mylohyoid
What is the raphe that lies inferiorly to the mylohyoid muscle called?
the median raphe
What is the action of the MYLOHYOID muscle when:
1) hyoid is fixed?
2) hyoid is not fixed?
1) Hyoid Fixed: jaw opening
2) Hyoid not fixed: raise hyoid and floor of mouth
What is the:
1) origin
2) insertion
of the anterior belly of digastric?
1) Origin: Digastric Fossa of the mandible
2) Insertion: intermediate tendon (secured to the hyoid bone by a fibrous loop
What is the action of the anterior belly of digastric when:
1) hyoid is fixed
2) hyoid is not fixed
1) Hyoid fixed: jaw opening
2) Hyoid not fixed: raise hyoid
What innervates the anterior belly of digastric?
CNVc Motor Root - via nerve to mylohyoid
What are the three muscles that fall under the “Hyoid Stabliser” group?
1) Infrahyoids (thyrohyoid, omohyoid, sternohyoid)
2) Posterior Digastric
3) Stylohyoid
What other two muscles are involved in mastication?
1) obicularis oris (oral sphincter)
2) buccinator (along with the tongue, helps control the bolus of food and direct it to posterior teeth)
What are the physiological chewing forces (N) in:
1) dentate patients?
2) edentulous patients?
1) dentate patients: 70-150N
2) edentulous patients: 4-55N
What is the maximum clenching force between molars (N)?
500-700N
