The Temporomandibular Joint and the Muscles of
Mastication
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The
temporal region | Main Anatomy
Index | The eye and orbit
Last updated 30 March 2006
The Temporomandibular Joint
- This articulation is a modified
hinge type of synovial joint.
- The articular surfaces are: (1) the head
or condyle of the mandible inferiorly and (2)
the articular tubercle
and the mandibular fossa
of the squamous part of the temporal bone.
- An oval fibrocartilaginous articular
disc divides the joint cavity into superior
and inferior compartments. The disc is fused
to the articular capsule surrounding the
joint.
- The articular disc is more firmly bound to the mandible
than to the temporal bone.
- Thus, when the head of the mandible
slides anterior on the articular tubercle as
the mouth is opened, the articular
disc slides anteriorly against the posterior surface of
the articular tubercle.
The
Articular Capsule (p. 731)
- The capsule of this joint is loose.
- The thin fibrous capsule is attached to the margins of the articular area on the
temporal bone and around the neck of the mandible.
Ligaments of the
Joint (p. 731)
- The fibrous
capsule is thickened laterally to form the lateral (temporomandibular) ligament.
It reinforces the lateral part of this capsule.
- The base of this triangular ligament is attached to the zygomatic process of the temporal bone
and the articular tubercle.
- Its apex is fixed to the lateral
side of the neck of the mandible.
- Two other ligaments connect the mandible to the cranium
but neither provides much strength.
- The stylomandibular ligament is a
thickened band of deep cervical fascia.
- It runs from the styloid process of the temporal bone to
the angle of the mandible and separates the parotid and
submandibular salivary glands.
- The sphenomandibular ligament
is a long membranous band that lies medial to the joint.
- This ligament runs from the spine of the sphenoid bone to
the lingula on the medial aspect of the mandible.
Movements
of the Temporomandibular Joint (p. 731)
- The two movements that occur at this joint are anterior gliding and a hinge-like rotation.
- When the mandible is depressed during opening of the
mouth, the head of the mandible and articular disc move
anteriorly on the articular surface until the head lies inferior to the articular
tubercle.
- As this anterior gliding occurs, the head
of the mandible rotates on the inferior surface of the
articular disc.
- This permits simple chewing or grinding movements over a
small range.
- Movements that are seen in this joint are: depression,
elevation, protrusion, retraction and grinding.
Muscles acting on the Temporomandibular Joint
- Movements of the temporomandibular joint are chiefly from
the action of the muscles of
mastication.
- The temporalis, masseter, and medial pterygoid muscles
produce biting movements.
- The lateral pterygoid muscles protrude the mandible with
the help from the medial pterygoid
muscles and retruded largely by the posterior
fibres of the temporalis muscle.
- Gravity is sufficient to depress the mandible, but if
there is resistance, the lateral
pterygoid, suprahyoid
and infrahyoid, mylohyoid and anterior digastric muscles are
activated.
Actions |
Muscles |
Depression (Open mouth) |
Lateral pterygoid |
Suprahyoid |
Infrahyoid |
|
Elevation (Close mouth) |
Temporalis |
Masseter |
Medial pterygoid |
|
Protrusion (Protrude chin) |
Masseter (superficial fibres) |
Lateral pterygoid |
Medial pterygoid |
|
Retrusion (Retrude chin) |
Temporalis |
Masseter (deep fibres) |
|
Side-to-side movements
(grinding and chewing) |
Temporalis on same side |
Pterygoid muscles of opposite side |
Masseter |
|
The
Temporalis Muscle (p. 733)
- This is an extensive fan-shaped muscle that covers the
temporal region.
- It is a powerful masticatory muscle that can easily be
seen and felt during closure of the mandible.
- Origin: floor of temporal fossa and deep surface of
temporal fascia.
- Insertion: tip and medial surface of coronoid process and
anterior border of ramus of mandible.
- Innervation: deep temporal branches of mandibular
nerve (CN V3).
- The temporalis elevates the mandible, closing the jaws;
and its posterior fibres retrude the mandible after
protrusion.
The
Masseter Muscle (p. 733)
- This is a quadrangular muscle that covers the lateral
aspect of the ramus and the coronoid process of the
mandible.
- Origin: inferior border and medial surface of zygomatic
arch.
- Insertion: lateral surface of ramus of mandible and its
coronoid process.
- Innervation: mandibular nerve
via masseteric nerve that enters its deep surface.
- It elevates and protrudes the mandible, closes the jaws
and the deep fibres
retrude it.
The
Lateral Pterygoid Muscle (p. 733)
- This is a short, thick muscle that has two heads or
origin.
- It is a conical muscle with its apex pointing
posteriorly.
- Origin: superior headinfratemporal surface and
infratemporal crest of the greater wing of the sphenoid
bone, inferior headlateral surface of lateral
pterygoid plate.
- Insertion: neck of mandible, articular disc, and capsule
of temporomandibular joint.
- Innervation: mandibular nerve
via lateral pterygoid nerve from anterior trunk, which
enters it deep surface.
- Acting together, these muscles protrude the mandible and
depress the chin.
- Acting alone and alternately, they produce side-to-side
movements of the mandible.
The
Medial Pterygoid Muscle (p. 733)
- This is a thick, quadrilateral muscle that also has two
heads or origin.
- It embraces the inferior head of the lateral pterygoid
muscle.
- It is located deep to the ramus of the mandible.
- Origin: deep headmedial surface of lateral
pterygoid plate and pyramidal process of palatine bone,
superficial headtuberosity of maxilla.
- Insertion: medial surface of ramus of mandible, inferior
to mandibular foramen.
- Innervation: mandibular nerve
via medial pterygoid nerve.
- It helps to elevate the mandible and closes the jaws.
- Acting together, they help to protrude the mandible.
- Acting alone, it protrudes the side of the jaw.
- Acting alternately, they produce a grinding motion.